SPU0410LR5H-QB Datasheet

Knowles

Download PDF Datasheet

Datasheet

Application Note
SiSonic
Design
Guide
Rev 3.0
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
2
of
30
Application Note
Table of Contents
1.0 MEMS MICROPHONE TECHNOLOGY .......................................................................... 3
2.0 CHOOSING THE RIGHT SISONIC MICROPHONE ...................................................... 3
2.1 PACKAGE TYPE ................................................................................................................. 3
2.2 OUTPUT FORMAT ............................................................................................................. 7
2.3 RF PROTECTION LEVEL ................................................................................................ 10
2.4 SISONIC PRODUCT MATRIX ........................................................................................ 12
3.0 MECHANICAL DESIGN CONSIDERATIONS .............................................................. 14
3.1 CHOOSING THE MIC AND PORT HOLE LOCATIONS .............................................. 14
3.2 ACOUSTIC PATH DESIGN ............................................................................................. 14
3.3 WIDEBAND FREQUENCY RESPONSE ......................................................................... 18
3.4 ECHO AND NOISE PROBLEMS ..................................................................................... 19
3.5 PCB LAND PATTERN AND SOLDER STENCIL PATTERN ....................................... 20
4.0 ELECTRICAL DESIGN CONSIDERATIONS ................................................................ 21
4.1 POWER SUPPLY ............................................................................................................... 21
4.2 GROUND ........................................................................................................................... 21
4.3 GAIN CONTROL ............................................................................................................... 21
4.4 MICROPHONE TO CODEC INTERFACE CIRCUIT ..................................................... 22
4.5 SISONIC 2-WIRE CIRCUIT ............................................................................................. 23
4.6 MINIMIZING NOISE PICK-UP ........................................................................................ 24
5.0 MANUFACTURING INFORMATION ............................................................................. 26
5.1 PICK-AND-PLACE SETTINGS........................................................................................ 26
5.2 REWORK ........................................................................................................................... 28
5.3 HANDLING AND STORAGE .......................................................................................... 28
5.4 QUALIFICATION TESTING ............................................................................................ 28
5.5 SENSITIVITY MEASUREMENTS .................................................................................. 30
6.0 ADDITIONAL RESOURCES ............................................................................................. 30
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
3
of
30
Application Note
1.0 MEMS MICROPHONE TECHNOLOGY
SiSonic MEMS microphones are on the cutting edge of acoustic technology and have gained
wide acceptance in many consumer electronics products including smart phones, feature phones,
entry phones, laptops, tablet PCs, netbooks, PDAs, and DSCs. The principle of operation for
SiSonic microphones is similar to that for traditional Electret Condenser Microphones (ECMs),
but since MEMS microphones are manufactured using silicon wafer processes they have smaller
form factors, improved performance in varied environmental conditions, and improved ease-of-
use in designs.
Purpose: This application note explains the package types, output formats, and RF protection
levels available in SiSonic microphones. It also provides information on mechanical design,
electrical design, and on using SiSonic microphones in a mass production environment.
2.0 CHOOSING THE RIGHT SISONIC MICROPHONE
SiSonic microphone models vary by package type, output format, and RF protection level.
The choice of package is driven by the mechanical requirements of the design, the output format
by the interface chipset and the application, and the RF protection level by the proximity to
antennas and other RF noise sources. The information in this section will help you choose the
right SiSonic microphone for your application.
2.1 PACKAGE TYPE
2.1.1 Top-port and Bottom-port SiSonic
Diagrams of the basic construction of SiSonic microphones and port-hole locations are shown in
the figures below.
Base
CMOS
Wall
MEMS
Acoustic Port Hole
Encapsulation
Diaphragm & Backplate
Back Volume
Wirebonds
Lid
Figure 1: The construction of a top-port SiSonic microphone
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
4
of
30
Application Note
CMOS
Wall
MEMS Acoustic Port Hole
Encapsulation
Diaphragm & Backplate Back Volume
Wirebonds
Lid
Base
Figure 2: The construction of a bottom-port Zero-Height SiSonic microphone
Top-port SiSonic microphones allow for traditional microphone placement and gasket design,
while bottom-port Zero-Height SiSonic microphones are particularly suited for ‘thin’ product
designs. Having both package choices gives designers more options for microphone placement
within the design constraints. The diagrams below show typical acoustic path mechanical
designs when using top-port and bottom-port microphones, along with typical frequency
responses for each package.
PCB
Standard Height
Product case
Gasket
Top-port SiSonic
Figure 3: Typical acoustic path design using a top-port SiSonic microphone
PCB
Zero-Height
SiSonic
Product case
Minimized Height
Gasket
Figure 4: Typical acoustic path design using a bottom-port Zero-Height SiSonic microphone
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
5
of
30
Application Note
-60
-55
-50
-45
-40
-35
-30
-25
-20
100 1,000 10,000 100,000
dB
Frequency (Hz)
Frequency Response
Top Port
SPA2410LR5H (bottom port)
Ultrasonic
Figure 5: Comparison of the frequency response of main SiSonic package types
2.1.2 Mesh Lid for Ultrasonic Applications
Ultrasonic SiSonic microphones have an open mesh lid design that uses an acoustically
transparent mesh as show in the picture below.
Figure 6: Mesh lid construction of ultrasonic mic
The open lid and mesh allow ultrasonic frequencies from 20 kHz to 80 kHz or more to be
captured by the MEMS. The frequency response of ultrasonic Sisonic is shown below.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
6
of
30
Application Note
-90.00
-80.00
-70.00
-60.00
-50.00
-40.00
1 10 100 1000 10000 100000
dB V/0.1Pa
Frequency (Hz)
SPM0404UD5 Typical Frequency Response
Figure 7: Ultrasonic SiSonic Frequency Response
The output of the ultrasonic SiSonic microphone must be processed by an amplifier, codec, or
A/D converter that can extract the ultrasonic frequencies needed by the application, usually by
using a higher sample rate and/or lower decimation rate. Ultrasonic SiSonic is ideally suited for
applications with natural ultrasonic emissions, or for those requiring a separate transmitter and
receiver or multiple transmitters at different frequencies. Potential applications include:
Consumer Products
o Ultrasonic pen
o Gesture recognition
Automotive Sensors:
o Parking assistant, curb detection
o Passenger detection (within cabin)
o Forward sensing of obstacles
Industrial Applications
o Equipment monitoring (mechanical attrition of ball-bearing)
o Position sensors (for plant use)
o Gas tube or pipe monitoring (flow or leaks)
o Security systems (motion detection)
Military
o Impulse detection (gunshot detection)
o Fire-arm positioning sensor
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
7
of
30
Application Note
2.1.3 Package Size
The microphone footprint decides the minimum PCB area required by the mic, and the mic
height sets the minimum vertical space required to integrate the mic into the final product.
Dimensions of each SiSonic package are shown in the table and figure below.
Package
name Port-hole location
Representative
Model numbers
Length
(mm)
Width
(mm)
Height
(mm)
Footprint
(mm
2
)
Mini
Top SPM0410HR5H
4.72 3.76 1.25 17.7 Bottom (Zero-Height) SPM0410LR5H
Mesh Top (Ultrasonic) SPM0404UD5 1.40
SPK Bottom (Zero-Height) SPK0413LM4H 4.00 3.00 1.00 12.0
Ultra
Mini
Top SPU0409HD5H
SPU0410HR5H 3.76 2.95 0.90
1.10 11.1
Bottom (Zero-Height) SPU0410LR5H 3.00 1.10 11.3
SPQ Top SPQ2410HR5H 3.76 2.24 1.10 8.4
SPA Bottom (Zero-Height) SPA2410LR5H 3.35 2.50 0.98 8.4
SPY Bottom (Zero-Height) SPY0824LR5H 3.00 1.90 0.90 5.7
Table 1: SiSonic Packages, Port-Hole Locations, and Dimensions
3.0 x
1.9 x
0.90
SPY
series
4.72 x 3.76
x 1.25mm
SPM series
Mini
3.76 x
2.95 x
1.10mm
SPU series
Ultra Mini
4.00 x
3.00 x
1.00mm
SPK Series
3.35 x
2.50 x
0.98
SPA
series
3.76 x
2.24 x
1.10
SPQ
series
Figure 8: Comparison of SiSonic Package Sizes
2.2 OUTPUT FORMAT
2.2.1 Unity-gain Analog and Amplified Outputs
Unity-gain SiSonic has a simple buffered output as shown in the figure below. A coupling
capacitor on the output is required to pass acoustic frequencies to the chipset input while
isolating the DC voltages. The coupling capacitor forms a high pass filter with the input
resistance of the next stage, and is typically 0.1µF or larger to give a corner frequency below
100Hz.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
8
of
30
Application Note
+Output
Ground
VDD
+
_
Figure 9: Unity-gain SiSonic Block Diagram
In far-field applications like teleconferencing and video recording, the desired acoustic signal is
in the mic far-field and may require additional amplification. Amplified SiSonic microphones
add up to 20dB of gain to the analog output signal before transmitting it to the chipset or audio
codec. Amplifying the signal at the mic versus at the codec improves the overall system Signal-
to-Noise Ratio (SNR) by increasing the transmitted signal size relative to noise in the traces.
The amplification in the mic and codec must be chosen appropriately so that the acoustic signal
does not saturate either mic or codec during operation.
+Output
Ground Gain Control
VDD
+
_
R1 = 22k
R2 = 2.44k
R3 (set by designer)
C1 (set by designer)
Figure 10: Amplified SiSonic Block Diagram
2.2.2 Differential SiSonic
SiSonic is also available with a differential output driver that offers stronger noise immunity than
a single-ended output due to the common mode rejection of noise picked up in traces.
Differential SiSonic includes an integrated amplifier that provides up to 14dB of additional
amplification. The figure below illustrates a typical differential circuit configuration.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
9
of
30
Application Note
Vdd
Ground
+
-
Output-
Output+
Gain Control
R1 = 9.8K
R2 = 2.44k
R3 (set by customer)
C1 (set by customer)
Figure 11: Block Diagram of Differential SiSonic with Amplified Output
2.2.3 Low Frequency SiSonic
Low frequency SiSonic is for applications such as music recording and automotive sensing
where low frequency audio signals are being captured. Low frequency SiSonic comes in an
Ultra Mini Zero-Height package, and has a low-frequency roll-off at about 5 Hz as shown below.
-20.00
-10.00
0.00
10.00
20.00
1 10 100 1000 10000
Relative Sensitivity (dB V/Pa)
Frequency (Hz)
Figure 12: Low Frequency SiSonic Frequency Response Curve
2.2.4 PDM Digital SiSonic
Pulse Density Modulated (PDM) Digital SiSonic microphones have a Sigma-Delta Analog to
Digital Converter (ADC) integrated into the microphone that accepts a 1.0 MHz to 3.25 MHz
clock, and returns over-sampled PDM data at the supplied clock frequency. Decimation and
filtering performed by the receiving chipset convert the PDM data stream into the PCM data for
use by application software. The primary advantage of the digital interface is noise immunity,
with secondary benefits of reduced overall system power consumption. Because the mic output
is a relatively large digital signal, only extreme noise can cause a bit change, and the half-cycle
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
10
of
30
Application Note
PDM format used makes the audio data relatively immune to even multi-bit errors. Digital
SiSonic microphones are ideal for designs requiring relatively long mic signal traces, especially
designs using multiple microphones. Mic traces can be routed to virtually any part of the design
with few constraints on routing and a higher probability of success with the first layout, at the
same time requiring fewer protective components.
The L/R select signal configures the microphone to drive the data line after either the rising edge
(Data_H) or falling edge (Data_L) of the clock. A Data_H and Data_L microphone can
multiplex data over the same output trace for multi-mic applications, reducing the interface pin
count. A basic block diagram of a Digital SiSonic design is shown in Figure 7.
Figure 13: PDM Digital SiSonic Interface
Digital SiSonic microphones require a chipset with a PDM audio interface. Contact Knowles for
more information on Digital SiSonic microphones and validated chipset vendors.
2.3 RF PROTECTION LEVEL
SiSonic microphones have integrated RF protection to help prevent RF noise from getting into
the acoustic signal. Standard SiSonic microphones have a grounded Faraday cage integrated into
the mic package, while Enhanced RF SiSonic microphones also have RC filters built into the
base PCB of the microphone. MaxRF SiSonic have the best RF performance, from a soldered
metal can package and RF filtering built into both the CMOS and the package of the
microphone. The figures below show conceptually how both radiated RF noise and conducted
RF noise are shorted to ground in RF-protected SiSonic mics.
DSP
Clock
(1.0 - 3.25 MHz)
Data
Cycle
PDM format)
L
R
L/R to Vdd for Data_H Mic
L/R to Gnd for Data_L
Two mic outputs can
be multiplexed on
same data line
Digital Sisonic
Vdd
Gnd
Gnd
Vdd
Digital Sisonic
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
11
of
30
Application Note
2.3.1 Standard and Enhanced RF SiSonic
Conducted Noise
Antenna
PCB
Ground Plane
Signal Trace
Ground
Signal
Radiated Noise
Figure 14: Enhanced RF SiSonic with FR4 package and filtering in the mic base
2.3.1 MaxRF SiSonic
Conducted Noise
Antenna
PCB
Ground Plane
Signal Trace
Ground
Signal
Radiated Noise
RC RC
Figure 15: MaxRF SiSonic with metal can package and additional filtering in the CMOS chip
Figure 16: Cross-section a metal can package
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
12
of
30
Application Note
2.4 SISONIC PRODUCT MATRIX
The table below summarizes the design needs, features, packages, and applications for the
various SiSonic models.
Design
Requirement
Mini
Mini
Zero-
Height
SPK
Zero-
Height
Ultra
Mini
Ultra
Mini
Zero-
Height
SPQ
SPA,
SPY
Zero-
Height
Benefit/application
SMD reflow X X X X X X X Mounted in standard lead-free
solder reflow processes
Thin design X X X X
Bottom-mount design allows
“zero” height requirements on
top side of PCB
Small
footprint X X X Minimal use of board space
Amplified
output X X X Far-field applications, improved
system SNR
Differential
output X Better noise immunity from
balanced design
Max RF
Protection X X X X X X Best RF noise immunity
Wind Noise
Filtering X X Higher low-frequency roll-off
reduces wind noise.
Digital PDM
interface X X
Best noise immunity, no analog
circuits in chipset, ideal for
multi-mic designs
Table 2: Summary of Design Needs met by SiSonic
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
13
of
30
Application Note
Package
name
Port-hole
location
Output Format RF Protection Representative
Model numbers
Mini
Top
Non-amplified
(analog)
Standard SPM0404HD5H
Enhanced SPM0404HE5H
Maximum SPM0410HR5H
Amplified (analog) Standard SPM0408HD5H
Enhanced SPM0408HE5H
Differential (analog) Enhanced SPM0406HE3H
Digital PDM Standard SPM0423HD4H
Enhanced SPM0423HM4H
Bottom
(Zero-Height)
Non-amplified
(analog)
Enhanced SPM0404LE5H
Maximum SPM0410LR5H
Amplified (analog) Enhanced SPM0408LE5H
Mesh Top Ultrasonic (analog) Standard SPM0404UD5
SPK Bottom
(Zero-Height) Digital PDM Enhanced SPK0813LM4H
Ultra Mini
Top
Non-amplified
(analog)
Standard SPU0409HD5H
Enhanced SPUL409HE5H
Maximum SPU0410HR5H
Amplified (analog) Maximum SPU0414HR5H
Bottom
(Zero-Height)
Non-amplified
(analog)
Enhanced SPU0409LE5H
Maximum SPU0410LR5H
Low Frequency Maximum SPU1410LR5H
SPQ Top Non-amplified
(analog) Maximum SPQ2410HR5H
SPA Bottom
(Zero-Height)
Non-amplified
(analog) Maximum SPA2410LR5H
SPY Bottom
(Zero-Height)
Non-amplified
(analog) Maximum SPY0824LR5H
Table 3: A Summary of Available SiSonic Models. (Please contact Knowles for the latest
information.)
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
14
of
30
Application Note
3.0 MECHANICAL DESIGN CONSIDERATIONS
The purpose of this section is to provide mechanical design information relating to the
microphone including:
Choosing locations for the mic(s) and acoustic port hole(s) in the case
Designing the acoustic path, including gasket design and assembly considerations
Designing for a wideband frequency response
Echo prevention and troubleshooting
Optimizing the land pattern, solder stencil design, and soldering process
3.1 CHOOSING THE MIC AND PORT HOLE LOCATIONS
Choosing a location for the microphone in a design can be challenging. For analog mics in
particular, the traces from mic to chipset should be kept as short as possible and as far as possible
from potential noise sources. However, the layout of many mobile product designs require that
the mic and traces be near antennas, power amplifiers, motors, hard disk drives, switching power
supplies, etc. The design engineer must also consider the available board space, component
height restrictions, port-hole location(s), acoustic path dimensions, and gasket size, location, and
ease-of-assembly in mass production when choosing a mic location.
The external acoustic port hole in the product housing should be located near the mic to simplify
the gasket and associated mechanical design. The port-hole must also be far enough from
speakers and other acoustic noise sources to minimize the strength of these unwanted signals at
the microphone input. In near-field use modes like talk mode in a mobile phone, the port-hole
location is more critical than in far-field modes since small changes in distance can change the
strength of the acoustic signal arriving at the microphone. In both types of applications, the port
hole should be located where it won’t be blocked during normal use.
If there are multiple mics in a design, then the mic and port-hole locations are further constrained
by the related product use-modes and any audio algorithm requirements. Picking good locations
for the microphones and port holes early in the design process can prevent costly PCB layout or
plastics changes late in the product design cycle.
3.2 ACOUSTIC PATH DESIGN
The acoustic path guides external sound into the microphone. The overall frequency response of
the microphone in the product design is determined by the standalone microphone frequency
response and the physical dimensions of each part of the acoustic path, including the case port-
hole, gasket(s), and PCB port-hole. The acoustic path must not have leaks that can cause echo or
noise problems, and needs to be designed for manufacturability.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
15
of
30
Application Note
3.2.1 Acoustic Path Dimensions
A short, wide acoustic path has minimal effects on the mic response while a long, narrow path
can create peaks in the audio band, potentially causing a “tinny” sound as higher frequencies are
amplified. A good acoustic path design gives a flat sensitivity frequency response across the
target acoustic frequency range. The designer must measure the frequency response of the
microphone with its acoustic path and make adjustments if the performance doesn’t meet design
goals. Possible changes include:
1. A larger case port hole
2. A thinner case at the case port hole
3. A wider gasket cavity
4. A shorter acoustic path from changing the mic or case port hole location
5. A larger and/or thinner PCB hole (for bottom-port mic designs)
6. Adding a screen or mesh as an acoustic resistance to extend the flat frequency response
range (see section 3.3)
The codec or baseband chipset that processes the audio signal from the mic generally includes a
low-pass filter with a cutoff frequency just above the desired acoustic range to remove the
unwanted higher frequency components. The frequency response curves below compare the
sensitivity of a standalone microphone, a microphone with a short, wide acoustic path design
(gasket A), a microphone with a long, narrow acoustic path design (gasket B), and both gaskets
with a 6 kHz filter representative of a typical low-pass digital filter.
-70
-60
-50
-40
-30
-20
-10
0
100 1000 10000
Sensitivity (dB)
Frequency (Hz)
Simulated Top-port Mic Response
Mic with gasket A
Mic with gasket B
Gasket A with 6kHz LPF
Gasket B with 6kHz LPF
Figure 17: The Effect of Acoustic Path Design on Microphone Frequency Response
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
16
of
30
Application Note
The gasket should provide a short, wide acoustic path from the port hole in the case to the
microphone. For designs using top-port SiSonic microphones, the gasket port-hole should have
at least a 0.5mm larger diameter than the microphone port hole to allow for x-y tolerances in the
gasket port-hole, mic port-hole, and gasket placement. At the same time, the gasket port-hole
must be small enough to ensure a complete seal of the gasket to the mic since any leaks could
cause echo, noise, or frequency response problems. A simple acoustic path design for a top-port
SiSonic microphone is shown below.
Microphone Port-Hole
Optional Screen
PCB
Standard Height
Product case
Top-port SiSonic
Noise
Case Port-Hole Gasket Cavity
Figure 18: A Simple, Effective Acoustic Path Design for a Top-Port Microphone
For designs using Zero-Height SiSonic microphones, the acoustic path also includes the solder
ring between the microphone and PCB, and the through-hole in the PCB. The PCB acoustic hole
must be large enough to give a good frequency response, but small enough for PCB design rules
governing the distance from solder pads to drilled holes. The inside of the PCB acoustic hole
must be un-plated so that solder will not wick into the hole and block the hole. A simple
acoustic path design for a bottom-port SiSonic microphone is shown below.
Optional
Screen
PCB
Zero-Height
SiSonic
Product case
Minimized Height
Microphone Port-Hole
Case Port-Hole
PCB Port-Hole
Noise
Gasket Cavity
Noise
Figure 19: A Simple, Effective Acoustic Path Design for a Bottom-Port Microphone
Knowles provides free simulation services for acoustic path designs. These simulations show the
approximate frequency response of SiSonic microphones with the gasket, case, and PCB to show
if the frequency response is appropriate for the application. A summary of some of the
recommended minimum dimensions for SiSonic acoustic path design is shown in the table
below. Case holes and gasket ports can be non-circular, and will generally give similar
performance as a circular hole with the same cross-sectional area.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
17
of
30
Application Note
Microphone Package
Microphone
Port-hole
diameter
Recommended
PCB Hole
Diameter
Recommended
Gasket Cavity
Diameter
Recommended
Case Hole
Diameter
Mini Top-port 0.84 mm N/A D > 1.5 mm 1.5 > D 1.0 mm
Mini Zero-Height
SPK Zero-Height
SPA Zero-Height
SPY Zero-Height
0.25 mm 0.9> D >0.4 mm D > 1.5 mm 1.5 > D 1.0 mm
Ultra Mini Top-port
SPQ Top-port 0.50 mm N/A D > 1.5 mm 1.5 > D 1.0 mm
Ultra Mini Zero-Height 0.25 mm 0.6> D >0.3 mm D > 1.5 mm 1.5 > D 1.0 mm
Table 4: Recommended Acoustic Path Dimensions
3.2.2 Gasket Material and Assembly
A gasket must be made of acoustically opaque material that prevents sound from passing through
it. The material must seal completely to the case and to the microphone or PCB. In a stack-up
tolerance analysis, the gasket must form a compression fit in worst case (large gap) conditions,
while compressing enough in small gap conditions to avoid bulges in the product case or the
walls of the acoustic path. Good acoustic sealing prevents echo, noise, and frequency response
problems that can result from resonant air volumes inside the product housing and from alternate
paths to the mic port-hole.
The manufacturability of the mic-gasket-case assembly must also be considered. The assembly
process must be designed to reliably align the holes in the gasket to the holes in the case and mic
or PCB in volume production. Side-port or end-port gasket designs are more difficult to
assemble, since the required gasket compression force is often parallel to the surface of the
microphone and perpendicular to the usual case compression force as shown in figure (a) below.
These types of gaskets can have problems with leaks during assembly, but a well-designed
assembly process or a gasket design such as that shown in (b) can form good seals.
PCB
End-port Gasket
Product case
Optional Screen
Top-port SiSonic
Compression Force
Potential gasket leak
Compression
Force
(a)
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
18
of
30
Application Note
PCB
End-port Gasket
Product case
Optional Screen
Top-port SiSonic
Compression Force
(b)
Figure 20: Example of an End-port Gasket Designs
Common gasket materials include various kinds of rubber and compressible, closed-cell foams.
Knowles can design and source gaskets for SiSonic microphones, so if interested please contact
Knowles for more information.
3.3 WIDEBAND FREQUENCY RESPONSE
Wideband and super wideband audio applications such as video and music recording use a
frequency range beyond the traditional communications voiceband of 3.4 kHz, and are
increasingly being used in new mobile product designs. A flat response is required from each
part of the design from microphone through the entire signal processing path. Bottom-port
SiSonic mics are well suited for wideband audio, but for top-port microphones the acoustic path
can cause a peak in the desired frequency range. In this case, the flat response can be extended
by adding acoustically resistive material such as a screen or mesh across the acoustic path of the
microphone to dampen the peak. An optimized gasket design together with an acoustic
resistance can extend the flat frequency response range of the top-port microphones to up to 15
kHz as shown in the figure below.
-70
-60
-50
-40
-30
-20
-10
0
100 1000 10000
Sensitivity (dB)
Frequency (Hz)
Mic and Gasket 1
Gasket 1, Screen 1
Gasket 1, Screen 2
Mic and Gasket 2
Gasket 2, Screen 3
Figure 21: Using an Acoustic Resistance Screen to Extend the Flat Frequency Response
An acoustic resistance can be inserted between gasket and microphone (top-port mics), gasket
and case, or PCB and gasket (bottom-port mics), and can also protect from dust and liquids.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
19
of
30
Application Note
Examples of possible acoustic resistance screen locations are shown in the figures in the previous
2 sections of this app note. The acoustic resistance of a material is inversely proportional to its
effective area, so a larger effective area has less resistance. A larger area also reduces the effect
of variations in the material properties. The thickness of the material should be taken into
account when calculating height stack-up tolerances and the compression of gasket materials.
3.4 ECHO AND NOISE PROBLEMS
Echo problems are most likely caused by a poor gasket seal. A leak in the gasket seal allows the
speaker output or other noise to propagate inside the product case into the mic port, with little
loss in strength. An easy way to test for a gasket leak is to block the acoustic port hole in the
case. If the echo problem persists, then the echo is likely caused by a gasket leak and can be
fixed by a gasket design change. A gasket leak may also cause the microphone to pick up audio
noise from other sources such as a camera zoom motor or a chirping capacitor. The figure below
shows a design with a gasket leak.
PCB
Top-port SiSonic
Product case
Gasket Leak
Noise from speaker,
motor, etc.
Figure 22: Echo or noise from a gasket leak.
In product use modes such as conference call mode the speaker output must be strong, so extra
care must be taken to prevent echo. Assuming a good gasket design between the microphone
and case, the strength of the speaker output at the microphone input is determined by the shortest
path from the speaker to the microphone for sound traveling outside of the product case. The
SPL output level of the speaker in open air decreases proportional to 1/R, and the sound intensity
with 1/R
2
. Once again, blocking the case port hole of the product can help determine if this is
the source of echo. If the echo disappears when the case port hole is blocked, then the speaker
output signal is too strong for the mic location. An external echo path such as this can be
addressed with the following changes:
1.
Reduce or limit the speaker output level.
2.
Increase the path length from speaker to microphone by changing the location of the
microphone and/or speaker in the design until the echo is reduced to an acceptable level.
3.
Use echo cancelation software to remove the speaker signal from the mic input.
The IntelliSonic software package from Knowles includes echo cancellation, noise cancellation,
and beam-forming functions for 2 microphone arrays for laptops using Windows 7/Vista.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
20
of
30
Application Note
IntelliSonic can reduce echo and remove background noise signals to significantly improve SNR.
Contact Knowles for further information about IntelliSonic.
3.5 PCB LAND PATTERN AND SOLDER STENCIL PATTERN
The PCB land pattern, the solder stencil pattern, the solder paste, and the reflow profile should
be designed to yield reliable solder joints. The solder joints serve as the electrical connection,
mechanical connection, and (for bottom-port mics) the acoustic seal between the mic and PCB.
The recommended PCB land pattern for each SiSonic model matches the microphone solder
pads dimensions. The solder stencil pattern must be optimized for production, and for bottom-
port SiSonic models must use a broken solder ring such as that shown in the figure below.
(a) (b)
Figure 23: Comparison of SPY Zero-Height SiSonic (a) microphone solder pads and (b) a non-
optimized reference solder stencil pattern with a broken solder ring.
The solder stencil and land patterns should be designed while considering PCB design rules,
solder type, reflow profile, solder stencil thickness, etc. Design optimizations could include:
1. Increasing the land pattern size symmetrically to extend beyond the edge of the mic to
allow for visual inspection of the solder joint.
2. Splitting round pads in the land pattern into two semicircles to allow for better out-
gassing during reflow and reduce the occurrence of bubbles.
3. For bottom-port mics, reducing the PCB hole diameter or increasing the solder ring
diameter to meet PCB design rule requirements.
4. Optimizing the solder reflow profile for each unique board design to ensure good solder
joints between the mic and PCB.
5. For bottom-port mics, reducing the solder flux content of solder paste to prevent
excessive flux from entering the mic port hole during reflow.
6. Increasing the solder stencil thickness to ensure adequate solder volume for good solder
joints.
7. Reducing the solder stencil thickness to reduce solder volume to minimize the occurrence
of solder balls.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
21
of
30
Application Note
4.0 ELECTRICAL DESIGN CONSIDERATIONS
The interface signals for analog SiSonic microphones include power, output, ground, and
sometimes additional signals. Since analog microphones have small amplitude outputs that are
susceptible to noise, care should be taken with the trace routing to avoid potential noise
problems. This section outlines recommendations for interfacing to each SiSonic signal, with an
emphasis on the interface between the microphone output and the codec or chipset.
4.1 POWER SUPPLY
SiSonic microphones have no change in sensitivity with supply voltage, so the system designer
only needs ensure that the supply voltage stays in the specified range, typically 1.5 to 3.6V.
Because SiSonic has a separate power supply line and an internal voltage regulator, it is less
susceptible to power supply noise than traditional ECMs. The Power Supply Rejection Ratio
(PSRR) for SiSonic microphones is typically 50dB before any amplification, but even with this
level of PSRR strong power supply noise can cause significant noise in the microphone output.
For example, a 10mV RMS noise signal attenuated by 50dB still results in a 30µV RMS ripple in
the microphone output. This can be significant compared to the 11µV RMS typical noise floor
of the microphone, and is equivalent to an acoustic input of about 46dB SPL. If there is strong
noise in the microphone power supply, then shunt capacitors may be added to stabilize the
supply as shown in Figure 28.
4.2 GROUND
All microphone ground pads should be connected to an analog ground plane through a short,
wide trace that is not daisy-chained from device to device. If there is strong noise in the ground
plane, some designs may benefit from a series ferrite bead in the ground path to isolate the
microphone from the noise. Amplified SiSonic models are designed to be drop-in replacements
for non-amplified models of the same package size, with one ground pad changed to be the gain
control pad. If it is anticipated that an amplified mic output may be needed in a design, the gain
control pad can be connected to ground through appropriate components to set the desired gain
(see the next section.) If non-amplified SiSonic is used in the final design, then the gain pad
components can be left unpopulated and the pad will be grounded internally by the non-
amplified mic.
4.3 GAIN CONTROL
The gain of amplified SiSonic microphones is set using a resistor and capacitor connected to the
Gain Control terminal of the microphone, as shown in the circuit below.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
22
of
30
Application Note
Figure 24: Gain control circuitry for amplified SiSonic
The value of R3 is chosen to give the desired gain value, with a maximum gain of 20dB when R3
is 0. C1 allows proper DC biasing of the amp input, and should be chosen so that the corner
frequency (C.F.) of the high-pass filter formed by C1, R2, and R3 is well below the acoustic
range. If no additional gain is required, the gain terminal can be tied directly to the output
terminal for the same sensitivity as a non-amplified SiSonic. The gain terminal cannot be left
floating since this will add noise to the mic output. R3 and C1 are calculated using the following
formulas:
Figure 25: Formulas for calculating gain control component values
The R and C components should be located as near to the microphone as possible, since any
noise picked up in the Gain Control terminal could feed into the output of the microphone.
4.4 MICROPHONE TO CODEC INTERFACE CIRCUIT
The interface circuit between an analog SiSonic microphone output and the codec or baseband
chipset can be very simple depending on the design needs. If the codec input is self-biasing, then
the only interface component required is a coupling capacitor. This capacitor forms a high pass
filter with the input impedance of the codec or chipset, so is typically in the µF range for a 3dB
point <100Hz. Some chipsets require an external DC bias circuit after the coupling capacitor,
C1 (set by customer)
R1 = 22k
R3 (set by customer)
R2 = 2.4k
V+
Term 2 = Gain Control
Term 3 = Ground
Term
4 =
Vout
Term 1 = Output
Setting Gain Formulas
:
Gain of non-inverting Op-Amp is determined as:
G=1+ {R1 / (R2 + R3)} Gain (dB) = 20 * log(G)
High-pass-filter Corner Frequency:
C.F. = 1 / {2π*(R2 + R3) * C1}
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
23
of
30
Application Note
and chipset documentation should be consulted for the recommended audio interface circuit.
Unlike ECMs, SiSonic microphones do not need a resistor from the output to power since they
have a separate power terminal and a built-in voltage regulator.
In general, the output trace should be kept as short as possible, and should be routed over or
between analog ground planes to shield it from noise. The figure below shows a simple
microphone interface circuit.
Figure 26: Example of a simple SiSonic interface circuit
4.5 SISONIC 2-WIRE CIRCUIT
Analog SiSonic microphones require a 3-wire interface, but for some applications like headsets a
2-wire interface is needed to reduce the number of conductors running through a cable. The 2-
wire circuit shown in the figures below uses a load circuit on the mic output node to generate an
AC current in the power node, which becomes the output of the 2-wire circuit. The output is
converted into a voltage when the current flows through the load resistor connected to the 2-wire
output.
V+
Out
GND
+
-
C
c
C
c
: 0.1
-
1.0
µ
F
coupling capacitor
V
sup
: 1.5 to 3.6V
DC
Codec or Baseband Chipset
C
c
SiSonic Microphone
Differential input
amplifier
Ana
log
Ground
0.7
-
1.0
V DC bias
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
24
of
30
Application Note
Figure 27: Circuit for 2-wire SiSonic microphone interface.
4.6 MINIMIZING NOISE PICK-UP
Many product designs like tablets and mobile handsets require the microphone(s) to be near
noise sources like antennas and power amplifiers. RF frequency signals are not themselves a
problem since they are well above audio frequencies, but many wireless standards use TDMA
technologies where data is sent in bursts or packets. The frequency of these packets usually falls
in the audio range and can induce an undesirable “buzz” in the audio signal.
In designs where noise is a concern, there are a number of techniques a designer can use to
protect the audio signal from noise.
1. Use MaxRF SiSonic models that have embedded RC filters on each trace to prevent RF
noise in traces from getting into the mic output. (See section 2.3)
2. Keep signal traces as far as possible from potential noise sources.
3. Route traces on inner PCB layers protected by ground layers, and keep trace lengths as
short as possible. Ideally Out and Vdd are connected directly to middle layers of the
PCB under the mic with vias.
4. Surround the microphone package with a ground plane if possible.
5. Add capacitor(s) between the microphone power and ground to help remove power
supply noise.
6. Use series ferrite beads (chokes) and RF shunt capacitors to reduce RF noise in traces.
Place ferrite beads near the mic or where traces come out from middle PCB layers, and
place caps on the chipset side of the ferrite beads.
7. DO NOT route the output and Vdd signals in parallel with no ground between, as this
could ruin cross-talk and multi-tone performance.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
25
of
30
Application Note
8. Use Differential or Digital SiSonic to minimize noise picked up by the output traces, or
configure single-ended SiSonic differentially by using the output and ground as the two
sides of a differential pair.
9. Place the microphone and associated circuitry in shielded areas of the design to reduce
the potential for RFI and EMI pick-up.
V+
Out
GND
+
-
C
rf
C
c
: 0.1-1.0µF
coupling capacitor
C
rf
: 10-100pF
close to device, RF optimized
V
sup
: 1.5 to 3.6V DC
Codec or Baseband Chipset
C
c
SiSonic Microphone
Differential input
amplifier
Analog
Ground
0.9-1.2V DC
F.B.
C
rf
C
pwr
: 0.1-10µF
Differential Traces:
•1 trace-width apart
•Over analog ground plane
Figure 28: Single-ended SiSonic design with noise protection techniques
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
26
of
30
Application Note
5.0 MANUFACTURING INFORMATION
SiSonic microphones are surface mount microphones intended for installation with standard
pick-and-place machinery for reflow onto a PCB with other surface mount components. Because
SiSonic microphones are acoustic components, they have some unique requirements in an
automated assembly line.
5.1 PICK-AND-PLACE SETTINGS
SiSonic microphones come in various size reels for use in auto pick-and-place machines. Exact
packaging information including pocket size and spacing is shown in each model’s specification.
The pick location for top-port models must be chosen so that the pick nozzle does not overlap the
port-hole of the microphone, while taking into account the microphone and pocket tolerances and
the pick nozzle shape, size, and placement accuracy. Bottom-port models may be picked
anywhere on the lid. The recommended pick areas for the SPQ and Ultra Mini SiSonic packages
are shown in the figures below.
Figure 29: SPQ SiSonic Pick Area.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
27
of
30
Application Note
Figure 30: Ultra Mini SiSonic Pick Area.
SiSonic microphones have gold-plated solder pads designed for use with lead-free solders. The
recommended solder stencil thickness range is 0.127 mm to 0.178 mm. SiSonic is guaranteed
for up to 3x passes through a lead-free solder reflow profile, and manufacturing line samples are
tested weekly with 5x reflows at the maximum profile conditions as part of On-going Reliability
Tests (ORTs). The exact reflow profile should be optimized for each design, but should not
exceed the maximum reflow profile for the microphone shown below:
Figure 31: SiSonic maximum solder reflow profile
170
180°C
Solder Melt
Pre
-
heat
260°
230°C
100 sec.
120 sec.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
28
of
30
Application Note
5.2 REWORK
Rework of Sisonic microphones is recommended using a temperature-ramp controlled system
such as an A.P.E. Chipper. The local area around the microphone can be heated until solder
reflow allows the microphone to be removed with a vacuum nozzle or tweezers. Installation of a
new microphone component is recommended using the same reflow profile used to install the
original component. Please contact Knowles for more information on the recommended rework
process.
5.3 HANDLING AND STORAGE
SiSonic microphones are installed using solder reflow processes, much earlier in the production
line than traditional ECMs. As a result, the downstream processes in the production line must be
reviewed to ensure that they do not damage the microphone. Information on handling and
storage for Sisonic microphones is listed below:
1. Shelf life: Twelve (12) months when devices are to be stored in factory supplied,
unopened ESD moisture sensitive bag under maximum environmental conditions of30ºC,
70% R.H.
2. MSL (moisture sensitivity level) Class 2a.
3. Do not pull a vacuum over port hole of the microphone. Pulling a vacuum over the port
hole can damage the device.
4. Do not board wash after the reflow process. Board washing and cleaning agents can
damage the device. Do not expose to ultrasonic processing or cleaning.
5. Do not brush board after the reflow process. Brushing the board with/without solvents
can damage the device.
6. Do not insert any object in port hole of device at any time as this can damage the device.
7. Number of reflows - Recommend no more than 3 cycles.
8. Do not vacuum seal static bags used to store unused portions of reels.
5.4 QUALIFICATION TESTING
SiSonic microphones give very consistent performance under extreme conditions. They are
resistant to power supply noise, mechanical shock, temperature, humidity, moisture
condensation, and vibration, and have no sensitivity variation over the specified supply voltage
range. A comparison of SiSonic and a typical ECM is shown for many of these characteristics in
the following table, and a graph of the vibration sensitivity of SiSonic vs. a typical ECM is
shown in the figure below.
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
29
of
30
Application Note
Feature SiSonic ECM
PSRR > 30dB (50dB typical) < 5dB (single-ended)
Mechanical Shock >10,000 G <5,000 G typical
Operating Temperature -40 C to +100 C -25 C to +85 C
Vibration Sensitivity ~ -74dBv/G ~ -62dBv/G
Change in Sensitivity with V
dd
No change, 1.5V to 3.6V
Max 3dB Loss at 1.5V
Table 5: SiSonic and ECM performance comparison
-90
-80
-70
-60
-50
-40
100 1000 10000
Frequency(Hz)
Sensitivity (dBv/G)
SiSonic
ECM
ECM w/ Gasket
Figure 32: Vibration Sensitivity Comparison of SiSonic and a typical ECM
SiSonic microphones are lead-free compliant and are certified Sony Green, and all Knowles
facilities are ISO certified. SiSonic microphones also undergo a regular battery of Ongoing
Reliability Tests (ORTs) to ensure consistent quality microphones. Additional qualification
testing is performed on all new designs to verify that the performance and quality of each
microphone is maintained. These additional tests are outlined in the table below:
Test Description
Thermal Shock 100 cycles of air-air thermal shock from -40°C to +125°C with 15min soaks.
(ICE 68-2-4)
High Temperature Storage +105°C environment for 1,000 hours. (IEC 68-2-2 Test Ba)
Low Temperature Storage -40°C environment for 1,000 hours. (IEC 68-2-2 Test Aa)
High Temperature Bias +105°C environment while under bias for 1,000 hours. (IEC 68-2-2 Test Ba)
SiSonic Design Guide - AN16
Confidential. Intended Customer’s Internal Use Only.
30
of
30
Application Note
www.knowles.com
AMERICAS:
Knowles Acoustics
1151 Maplewood Drive
Itasca, IL 60143
U.S.A.
Phone: 630-250-5930
Fax: 630-250-5932
EUROPE:
Knowles Electronics Denmark
Havnevej 7
DK-4000 Roskilde
Denmark
Phone: +45 7025 3570
Fax: +45 7025 3571
JAPAN:
Knowles Electronics Japan KK
2-2-16 Sangenjaya, Setagaya-Ku,
Tokyo 154-0024,
Japan
Phone: 81-3-5779-8503
Fax: 81-3-5779-8523
ASIA:
Knowles Acoustics
5F, No. 129, Lane 235, Bauchiau Rd.
Shindian City, Taipei 231, Taiwan
Republic of China
Phone: 886-2-8919-1799
Fax: 886-2-8919-1798
Low Temperature Bias -40°C environment while under bias for 1,000 hours. (IEC 68-2-2 Test Aa)
Temperature / Humidity Bias
+85°C/85% RH environment while under bias for 1,000 hours. (JESD22-
A101A-B)
Vibration
4 cycles lasting 12 minutes from 20 to 2,000Hz in X, Y, and Z direction with
a peak acceleration of 20g. (MIL 883E, Method 2007.2, A)
Electrostatic Discharge 3 discharges at +/- 8kV direct contact to the lid when unit is grounded (IEC
1000-4-2) and 3 discharges at +/- 2kV direct contact to the I/O pins (MIL
883E, Method 3015.7)
Reflow 5 reflow cycles with peak temperature of +260°C.
Mechanical Shock 3 pulses of 5,000g in the X, Y, and Z direction. (IEC 68-2-27, Test Ea)
Table 6: SiSonic Qualification Tests
5.5 SENSITIVITY MEASUREMENTS
Accurate sensitivity measurements can be made in an anechoic chamber, where an acoustic
signal from a speaker is captured by the test microphone in a noise-free environment and a
reference microphone is used to calibrate out any non-linearities of the speaker and chamber.
During final test in the SiSonic production lines, sensitivity is measured on 100% of
microphones using a reference microphone and a brass box that isolates microphones from
environmental noise.
Knowles can also provide Portable Test Jigs (PTJs) for quick sensitivity measurements of
individual microphones using an oscilloscope or multimeter to measure the microphone output.
An output (V
O
) measured in RMS volts can be converted to sensitivity (S) in dB using the
formula S = 20*log(V
O
/1V). Contact Knowles for more information on sensitivity
measurements using PTJs.
6.0 ADDITIONAL RESOURCES
For more information on SiSonic microphones, see the Knowles Acoustics web site at
www.knowles.com or contact your local Knowles sales office listed at the end of this document.
Date: August 22, 2011
Version: 3.0

Products

SPU-BOTTOM MIC IOT FOCUSED MIC
Available Quantity61572
Unit Price1.15
SPU-TOP MIC IOT FOCUSED MIC
Available Quantity430141
Unit Price1.27
MIC SISONIC ZERO HEIGHT DIGITAL
Available Quantity16066
Unit Price1.89
SISONIC MIC AMPLIFIED TOP PORT
Available Quantity70924
Unit Price2.41
MIC MEMS DIGITAL PDM OMNI -26DB
Available Quantity14405
Unit Price3.14
MIC SISONIC SLIM ULTRAMINI RF
Available Quantity3378
Unit Price2.1
MIC MEMS ANALOG OMNI -42DB
Available Quantity5440
Unit Price6.9
MIC MEMS ANALOG OMNI -42DB
Available Quantity756
Unit Price2.17
MIC MEMS ANALOG OMNI -42DB
Available Quantity23
Unit Price2.34
MIC MEMS ANALOG OMNI -38DB
Available Quantity0
Unit Price0
MIC MEMS ANALOG OMNI -22DB
Available Quantity0
Unit Price0
MIC MEMS ANALOG OMNI -42DB
Available Quantity0
Unit Price0
MIC MEMS ANALOG OMNI -42DB
Available Quantity0
Unit Price0
MIC MEMS ANALOG OMNI -38DB
Available Quantity0
Unit Price0