2516

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Functional Block Diagram
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Product Description
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Ordering Information
Prescaler
32/64
Phase
Detector &
Charge Pump
Lock
Detect
LOOP FLT
14
16
DIV CTRL
DC
Bias
5TX OUT
2
OSC E
1
OSC B
15
LD FLT
MOD IN
8
RESNTR+
13
RESNTR-
12
3PD
RF2516
VHF/UHF TRANSMITTER
The RF2516 is a monolithic integrated circuit intended for use as a low-
cost AM/ASK transmitter. The device is provided in a 16-pin QSOP-16
package and is designed to provide a phased locked frequency source for
use in local oscillator or transmitter applications. The chip can be used in
applications in the North American and European VHF/UHF bands. The
integrated VCO, phase detector, prescaler, and reference oscillator transis-
tor require only the addition of an external crystal to provide a complete
phase-locked loop. In addition to the standard power-down mode, the chip
also includes an automatic lock-detect feature that disables the transmit-
ter output when the PLL is out-of-lock.
Features
Fully Integrated PLL Circuit
Integrated VCO and Refer-
ence Oscillator
2.25V to 3.6V Supply Voltage
Low Current and Power Down
Capability
100MHz to 500MHz Fre-
quency Range
Out-of-Lock Inhibit Circuit
Applications
315/433MHz Band Systems
Local Oscillator Source
Part 15.231 Applications
Remote Keyless Entry
Wireless Security Systems
AM/ASK/OOK Transmitter
RF2516 VHF/UHF Transmitter
RF2516PCBA-410 Fully Assembled Evaluation Board
Rev A17 DS060712
9
RF2 516
VHF/UHF
Tra ns m it te r
RoHS Compliant & Pb-Free Product
Package Style: SSOP-16
RFMD m mm: mm
2 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Absolute Maximum Ratings
Parameter Rating Unit
Supply Voltage -0.5 to +3.6 VDC
Power Down Voltage (VPD) -0.5 to VCC V
MOD IN -0.5 to 1.1 V
Operating Ambient Temperature -40 to +85 °C
Storage Temperature -40 to +150 °C
Parameter Specification Unit Condition
Min. Typ. Max.
Overall T=25°C, VCC =2.8V, Freq=433MHz,
RMODIN =3kΩ
Frequency Range 100 to 500 MHz
Modulation AM/ASK
Modulation Frequency 1 MHz
Incidental FM 15 kHz p-p
Output Power +8.5 +10 dBm 50Ω load
ON/OFF Ratio 75 dB
PLL and Prescaler
Prescaler Divide Ratio 32/64
VCO Gain, KVCO 20 MHz/V Frequency and board layout dependent.
PLL Phase Noise -97 dBc/Hz 10kHz Offset, 50kHz loop bandwidth
-102 dBc/Hz 100kHz Offset, 50kHz loop bandwidth
Harmonics -60 dBc With output tuning.
Reference Frequency 17 MHz
Crystal Frequency Spurs -50 dBc 50kHz PLL loop bandwidth
Max Crystal RSTBD 35 50 ΩFor a typ. 1ms turn-on time.
Max Crystal Motional Inductance 60 mH For a typ. 1ms turn-on time.
Charge Pump Current 100 μAK
PD=100μA/2π=0.0159mA/rad
Power Down Control
Power Down “ON” VCC- 0.3V V Voltage supplied to the input; device is “ON”
Power Down “OFF” +0.3 V Voltage supplied to the input; device is “OFF”
Control Input Impedance 100k Ω
Turn On Time 1 2 ms Crystal start-up, 13.57734MHz crystal.
Turn Off Time 1 2 ms
Power Supply
Voltage 2.8 V Specifications
2.25 3.6 V Operating limits
Current Consumption (Avg.) 6 10.5 mA 50% Duty Cycle 10kHz Data applied to the
MOD IN input. RMODIN (R10)=3kΩ. Output
power/DC current consumption externally
adjustable by modulation input resistor (see
applicable Application Schematic).
Power Down Current 0 1 uA PD=0V, MOD IN=0V, DIV CTRL=0V
Caution! ESD sensitive device.
Exceeding any one or a combination of the Absolute Maximum Rating conditions may
cause permanent damage to the device. Extended application of Absolute Maximum
Rating conditions to the device may reduce device reliability. Specified typical perfor-
mance or functional operation of the device under Absolute Maximum Rating condi-
tions is not implied.
RoHS status based on EUDirective2002/95/EC (at time of this document revision).
The information in this publication is believed to be accurate and reliable. However, no
responsibility is assumed by RF Micro Devices, Inc. ("RFMD") for its use, nor for any
infringement of patents, or other rights of third parties, resulting from its use. No
license is granted by implication or otherwise under any patent or patent rights of
RFMD. RFMD reserves the right to change component circuitry, recommended appli-
cation circuitry and specifications at any time without prior notice.
T cf: RFMD mm
3 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Pin Function Description Interface Schematic
1OSC B
This pin is connected directly to the reference oscillator transistor base.
The intended reference oscillator configuration is a modified Colpitts. A
68pF capacitor should be connected between pin 1 and pin 2.
2OSC E
This pin is connected directly to the emitter of the reference oscillator tran-
sistor. A 33pF capacitor should be connected from this pin to ground.
See pin 1.
3PD
Power Down control for all circuitry. When this pin is a logic “low” all circuits
are turned off. When this pin is a logic “high”, all circuits are operating nor-
mally. A “high” is VCC. Diodes shown in the interface schematic provide
3kV electrostatic discharge (ESD) protection using the human body model.
4GND
Ground connection for the TX OUT amp. Keep traces physically short and
connect immediately to ground plane for best performance. Diodes shown
in the interface schematic provide 3kV electrostatic discharge (ESD) pro-
tection using the human body model.
5TXOUT
Transmitter output. This output is an open collector and requires a pull-up
inductor for bias/matching and a tapped capacitor for matching.
6GND1
Ground connection for the TX output buffer amplifier. Diodes shown in the
interface schematic provide 3kV electrostatic discharge (ESD) protection
using the human body model.
7VCC1
This pin is used to supply bias to the TX buffer amplifier. Diodes shown in
the interface schematic provide 3kV electrostatic discharge (ESD) protec-
tion using the human body model.
8MOD IN
AM analog or digital modulation can be imparted to the carrier by an input
to this pin. An external resistor is used to bias the output amplifiers through
this pin. The voltage at this pin must not exceed 1.1V. Higher voltages may
damage the device. Diodes shown in the interface schematic provide 3kV
electrostatic discharge (ESD) protection using the human body model.
9VCC2
This pin is used to supply DC bias to the VCO, crystal oscillator, pre-scaler,
phase detector, and charge pump. An IF bypass capacitor should be con-
nected directly to this pin and returned to ground. Diodes shown in the
interface schematic provide 3kV electrostatic discharge (ESD) protection
using the human body model.
See pin 7.
10 GND2 Digital PLL ground connection. Diodes shown in the interface schematic
provide 3kV electrostatic discharge (ESD) protection using the human body
model.
OSC E
VCC
OSC B
V
CC
PD
TX OUT
MOD IN
RF IN
VCC1
V
CC
1 k
Ω
MOD IN
TX OUT
V
CC
GND
VCC
mmmmmmm
4 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Pin Function Description Interface Schematic
11 VREF P Bias voltage reference pin for bypassing. The bypass capacitor should be of
appropriate size to provide filtering of the reference crystal frequency and
be connected directly to this pin. Diodes shown in the interface schematic
provide 3kV electrostatic discharge (ESD) protection using the human body
model.
12 RESNTR- The RESNTR pins are used to supply DC voltage to the VCO, as well as to
tune the center frequency of the VCO. Equal value inductors should be con-
nected to this pin and pin 13.
13 RESNTR+ See pin 12.
14 LOOP FLT Output of the charge pump. An RC network from this pin to ground is used
to establish the PLL bandwidth. Diodes shown in the interface schematic
provide 3kV electrostatic discharge (ESD) protection using the human body
model.
15 LD FLT This pin is used to set the threshold of the lock-detect circuit. A shunt
capacitor should be used to set an RC time constant with the on-chip
series 1k resistor. This signal is used to clamp (enable or disable) the MOD
IN circuitry. The time constant should be approximately 10 times the refer-
ence period. Diodes shown in the interface schematic provide 3kV electro-
static discharge (ESD) protection using the human body model.
16 DIV CTRL Logic “High” input selects divide-by-64 prescaler. Logic “Low” input selects
divide-by-32 prescaler. Diodes shown in the interface schematic provide
3kV electrostatic discharge (ESD) protection using the human body model.
RESNTR-RESNTR+
LOOP FLT 4 k
Ω
LOOP FLT
V
CC
V
CC
LD FLT
1 k
Ω
V
CC
DIV CTRL
mmmmmmm I l «w fifififififififi UUUUUUUU %+ T L Dr T a 4‘; 4
5 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Package Drawing
0.157
0.150
0.196
0.189
0.2440
0.2284
0.0688
0.0532
0.050
0.016
0.0098
0.0075
8° MAX
0°MIN
NOTES:
1. Shaded lead is Pin 1.
2. All dimensions are excluding mold flash.
3. Lead coplanarity - 0.005 with respect to datum "A".
0.012
0.008
0.025
-A-
0.0098
0.0040
mmmmmmm
6 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
RF2516 Theory of Operation
Introduction
Short range radio devices are becoming commonplace in today’s environment. The most common examples are the remote
keyless entry systems popular on many new cars and trucks, and the ubiquitous garage door opener. Other applications are
emerging with the growth in home security, automation and the advent of various remote control applications. Typically these
devices have been simplex, or one-way, links. They are also typically built using surface acoustic wave (SAW) devices as the fre-
quency control elements. This approach has been attractive because the SAW devices have been readily available and a trans-
mitter, for example, could be built with only a few additional components. Recently however, RF Micro Devices, Inc. (RFMD), has
introduced several new components that enable a new class of short-range radio devices based on the use of crystals and
phase-locked loops for frequency control. These devices are superior in performance and comparable in cost to the traditional
SAW-based designs. The RF2516 is an example of such a device. The RF2516 is targeted for applications such as 315MHz
and 433MHz band remote keyless entry systems and wireless security systems, as well as other remote control applications.
The RF2516 Transmitter
The RF2516 is a low-cost AM/ASK VHF/UHF transmitter designed for applications operating within the frequency range of
100MHz to 500MHz. In particular, it is intended for 315MHz to 433MHz band systems, remote keyless entry systems, and
FCC Part 15.231 periodic transmitters. It can also be used as a local oscillator signal source. The integrated VCO, phase detec-
tor, prescaler, and reference oscillator require only the addition of an external crystal to provide a complete phase-locked loop.
In addition to the standard power-down mode, the chip also includes an automatic lock-detect feature that disables the trans-
mitter output when the PLL is out-of-lock.
The device is manufactured on a 25GHz Silicon Bipolar-CMOS process and packaged in an industry standard SSOP-16 plastic
package. This, combined with the low external parts count, enables the designer to achieve small-footprint, high-performance,
low-cost designs.
The RF2516 is designed to operate from a supply voltage ranging from 2.25V to 3.6V, accommodating designs using three
NiCd battery cells, two AAA flashlight cells, or a lithium button battery. The device is capable of providing up to +10dBm output
power into a 50Ω load, and is intended to comply with FCC requirements for unlicensed remote control transmitters. ESD pro-
tection is provided on all pins except VCO and TX OUT.
While this device is intended for OOK operation, it is possible to use narrowband FM. This is accomplished by modulating the
reference oscillator rather than applying the data to the MOD IN input pin. The MOD IN pin should be tied high to cause the
device to transmit. The deviation will be set by pulling limits of the crystal. Deviation sufficient for the transmission of voice and
other low data rate signals can therefore be accomplished. Refer to the Application Schematic in the data sheet for details.
The RF2516 Functional Blocks
A PLL consists of a reference oscillator, a phase detector, a loop filter, a voltage controlled oscillator (VCO), and a programma-
ble divider in the feedback path. The RF2516 includes all of these internally, except for the loop filter and the reference oscilla-
tor’s crystal and two feedback capacitors.
The reference oscillator is a Colpitts type oscillator. Pins 1 (OSC B) and 2 (OSC E) provide connections to a transistor that is
used as the reference oscillator. The Colpitts configuration is a low parts count topology with reliable performance and reason-
able phase noise. Alternatively, an external signal could be injected into the base of the transistor. The drive level should, in
either case, be around 500mVPP
. This level prevents overdriving the device and keeps the phase noise and reference spurs to
a minimum.
The prescaler divides the VCO frequency by either 64 or 32, using a series of flip-flops, depending upon the logic level present
at the DIV CTRL pin. A high logic level will select the 64 divisor. A low logic level will select the 32 divisor. This divided signal is
then fed into the phase detector where it is compared with the reference frequency.
mmmmmmm
7 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
The RF2516 contains an onboard phase detector and charge pump. The phase detector compares the phase of the reference
oscillator to the phase of the VCO. The phase detector is implemented using flip-flops in a topology referred to as either “digital
phase/frequency detector” or “digital tri-state comparator”. The circuit consists of two D flip-flops whose outputs are combined
with a NAND gate which is then tied to the reset on each flip-flop. The outputs of the flip-flops are also connected to the charge
pump. Each flip-flop output signal is a series of pulses whose frequency is related to the flip-flop input frequency.
When both inputs of the flip-flops are identical, the signals are both frequency- and phase-locked. If they are different, they will
provide signals to the charge pump which will either charge or discharge the loop filter, or enter into a high impedance state.
The name “tri-state comparator” comes from this.
The main benefit of this type of detector is the ability to correct for errors in both phase and frequency. When locked, the detec-
tor uses phase error for correction. When unlocked, it uses frequency error for correction. This type of detector will lock under
all conditions.
The charge pump consists of two transistors, one for charging the loop filter and the other for discharging the loop filter. Its
inputs are the outputs of the phase detector flip-flops. Since there are two flip-flops, there are four possible states. If both
amplifier inputs are low, then the amplifier pair goes into a high impedance state, maintaining the charge on the loop filter. The
state where both inputs are high will not occur. The other states are either charging or discharging the loop filter. The loop filter
integrates the pulses coming from the charge pump to create a control voltage for the voltage controlled oscillator.
The VCO is a tuned differential amplifier with the bases and collectors cross-coupled to provide positive feedback and a 360°
phase shift. The tuned circuit is located in the collectors, and is comprised of internal varactors and external inductors. The
designer selects the inductors for the desired frequency of operation. These inductors also provide DC bias for the VCO.
The output of the VCO is buffered and applied to the prescaler circuit, where it is divided by either 32 or 64, as selected by the
designer, and compared to the reference oscillator frequency.
The transmit amplifier is a two-stage amplifier consisting of a driver and an open collector final stage. It is capable of providing
10dBm of output power into a 50Ω load while operating from a 3.6V power supply.
The lock-detect circuitry connects to the output of the phase detector circuitry and is used to disable the transmitter when the
VCO is not phase-locked to the reference oscillator. This is necessary to avoid unwanted out-of-band transmission and to pro-
vide compliance with regulatory limits during an unlocked condition.
There are many possible reasons for the PLL not to be locked. For instance, there is a short period during the start of any VCO
in which the VCO begins oscillating and the reference oscillator builds up to full amplitude. During this period, the frequency
will likely be outside the authorized band. Typically, the VCO starts much faster than the reference oscillator. Once both VCO
and reference oscillators are running, the phase detector can start slewing the VCO to the correct frequency, slowly sliding
across 200MHz of occupied spectrum. In competitive devices, the VCO radiates at full power under all of these conditions.
The lock protection circuit in the RF2516 is intended to stabilize quickly after power is applied to the chip, and to disable the
base drive to the transmit amplifier. This attenuates the output to levels that will be generally acceptable to regulatory boards
as spurious emissions. Once the phase detector has locked the oscillators, then the lock circuit enables the MOD IN pin for
transmission of the desired data. There is no need for an external microprocessor to monitor the lock status, although that can
be done with a low current A/D converter in a system micro, if needed. The lock-detect circuitry contains an internal resistor
which, combined with a designer-chosen capacitor for a particular RC time constant, filters the lock-detect signal. This signal is
then passed through an internal Schmitt trigger and used to enable or disable the transmit amplifier.
If the oscillator unlocks, even momentarily, the protection circuit quickly disables the output until the lock is stable. These
unlocks can be caused by low battery voltage, poor power supply regulation, severe shock of the crystal or VCO, antenna load-
ing, component failure, or a myriad of unexpected single-point failures.
The RF2516 contains onboard band gap reference voltage circuitry which provides a stable DC bias over varying temperature
and supply voltages. Additionally, the device features a power-down mode, eliminating battery disconnect switches.
‘an mmmmmmm
8 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Designing With the RF2516
The reference oscillator is built around the onboard transistor at pins 1 and 2. The intended topology is that of a Colpitts oscil-
lator. The Colpitts oscillator is quite common and requires few external components, making it ideal for low-cost solutions. The
topology of this type of oscillator is as seen in the following figure.
This type of oscillator is a parallel resonant circuit for a fundamental mode crystal. The transistor amplifier is an emitter fol-
lower and the voltage gain is developed by the tapped capacitor impedance transformer. The series combination of C1 and C2
act in parallel with the input capacitance of the transistor to capacitively load the crystal.
The nominal capacitor values can be calculated with the following equations6:
and
The load capacitance is usually 32pF. The variable freq is the oscillator frequency in MHz. The frequency can be adjusted by
either changing C2 or by placing a variable capacitor in series with the crystal. As an example, assume a desired frequency of
14MHz and a load capacitance of 32pF. C1=137.1pF and C2=41.7pF.
These capacitor values provide a starting point. The drive level of the oscillator should be checked by looking at the signal at
pin 2 (OSC E). It has been found that the level at this pin should generally be around 500mVPP or less. This will reduce the ref-
erence spur levels and reduce noise from distortion. If this level is higher than 500mVPP then increase the value of C1. The val-
ues of these capacitors are usually tweaked during design to meet performance goals, such as minimizing the start-up time.
Additionally, by placing a variable capacitor in series with the crystal, one is able to adjust the frequency. This will also alter the
drive level, so it should be checked again.
An important part of the overall design is the voltage controlled oscillator. The VCO is configured as a differential amplifier. The
VCO is tuned via internal varactors. The varactors are tuned by the loop filter output voltage through a 4kΩ resistor.
X1 C2
C1
V
CC
C1
60 Cload
⋅
freqMHz
------------------------
=
C21
1
Cload
------------- 1
C1
------
–
--------------------------
=
mmmmmmm HHi 4MP
9 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
As mentioned earlier, the inductors and the varactors are tuning a differential amplifier. To tune the VCO the designer only
needs to calculate the value of the inductors connected to pins 12 and 13 (RESNTR- and RESNTR+). The inductor value is
determined by the equation:
In this equation, f is the desired operating frequency and L is the value of the inductor required. The value C is the amount of
capacitance presented by the varactors and parasitics. For calculation purposes 1.5pF should be used. The factor of one-half
is due to the inductors being in each leg. As an example, assume an operating frequency of 433MHz. The calculated value of
each inductor is 45nH. A 47nH inductor would be appropriate as the closest available value.
The setup of the VCO can be summarized as follows. First, open the loop. Next, get the VCO to run on the desired frequency by
selecting the proper inductor and capacitor values. The capacitor value will need to include the varactor and circuit parasitics.
After the VCO is running at the desired frequency, set the VCO sensitivity. The sensitivity is determined by connecting the con-
trol voltage input point to ground and noting the frequency.
Connect the same point to the supply, and again note the frequency. The difference between these two frequencies divided by
the supply voltage is the VCO sensitivity expressed in Hz/V. Increasing the inductor value while decreasing the capacitor value
will increase the sensitivity. Decreasing the inductor value while increasing the capacitor value will lower the sensitivity.
When increasing or decreasing component values, make sure that the center frequency remains constant. Finally, close the
loop.
External to the part, the designer needs to implement a loop filter to complete the PLL. The loop filter converts the output of
the charge pump into a voltage that is used to control the VCO. Internally, the VCO is connected to the charge pump output
through a 4kΩ resistor. The loop filter is then connected in parallel to this point at pin 14 (LOOP FLT). This limits the loop filter
topology to a second order filter usually consisting of a shunt capacitor and a shunt series RC. A passive filter is most common,
as it is a low-cost and low-noise design. An additional pole could be used for reducing the reference spurs, however there is not
a way to add the series resistor. However, this should not be a reason for concern.
4 k
Ω
LOOP FLT
L L
RESNTR+ RESNTR-
L1
2πf⋅⋅
----------------
⎝⎠
⎛⎞
21
C
----1
2
---
⋅⋅=
~04in mmmmmmm
10 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
The schematic of the loop filter is:
The transfer function is:
where the time constants are defined as:
and
The frequency at which unity gain occurs is given by:
This is also the loop bandwidth.
If the phase margin (PM) and the loop bandwidth (ωLBW) are known, it is possible to calculate the time constants. These are
found using the equations4:
and
4 k
Ω
LOOP FLT
L L
RESNTR+ RESNTR-
Fs() R2
sτ21+⋅
sτ2sτ11)+⋅(⋅⋅
-------------------------------------------
⋅=
τ2R2C2
⋅=
τ1R2
C1C2
⋅
C1C2
+
------------------- ⎠
⎞
⎝
⎛
⋅=
ωLBW 1
τ1τ2
⋅
-------------------
=
τ1PM()sec PM()tan–
ωLBW
--------------------------------------------------
=
τ21
ωLBW
2τ1
⋅
------------------------
=
mmmmmmm
11 of 22
RF2516
Rev A17 DS060712
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support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
With these known, it is then possible to determine the values of the filter components.4
As an example, consider a loop bandwidth of 50kHz, a phase margin of 45°, a divide ratio of 64, a KVCO of 20MHz/V, and a
KPD of 100μA/2πrad. Time constant τ1 is 1.31848μs, time constant τ2 is 7.68468μs, C1 is 20.9pF, C2 is 100.8pF, and R2 is
76.2 kΩ.
In order to perform these calculations, one will need to know the value of two constants, KVCO and KPD. KPD is calculated by
dividing the charge pump current by 2π. For the RF2516, the charge pump current is 100μA. KVCO is best found empirically as
it will change with frequency and board parasitics. By briefly connecting pin 14 (LOOP FLT) to VCC and then to ground, the fre-
quency tuning range of the VCO can be seen. Dividing the difference between these two frequencies by the difference in the
voltage gives KVCO in MHz/V.
The control lines provide an interface for connecting the device to a microcontroller or other signal generating mechanism. The
designer can treat pin 8 (MOD IN), pin 16 (DIV CTRL), and pin 3 (PD) as control pins whose voltage level can be set. The lock-
detect voltage at pin 15 (LD FLT) is an output that can be monitored by the microcontroller.
Pin 15 (LD FLT) is used to set the threshold of the lock-detect circuit. A shunt capacitor is used to set an RC time constant with
an on-chip series 1kΩ resistor. The time constant should be approximately 10 times the reference period.
General RF bypassing techniques must be observed to get the best performance. Choose capacitors such that they are series
resonant near the frequency of operation.
Board layout is always an area in which great care must be taken. The board material and thickness are used in calculating the
RF line widths. The use of vias for connection to the ground plane allows one to connect to ground as close as possible to
ground pins. When laying out the traces around the VCO, it is desirable to keep the parasitics equal between the two legs. This
will allow equal valued inductors to be used.
Pre-compliance testing should be performed during the design process. This can be done with a GTEM cell or at a compliance
testing laboratory. It is recommended that pre-compliance testing be performed so that there are no surprises during final
compliance testing. This will help keep the product development and release on schedule.
Working with a laboratory offers the benefit of years of compliance testing experience and familiarity with the regulatory
issues. Also, the laboratory can often provide feedback that will help the designer make the product compliant.
On the other hand, having a GTEM cell or an open air test site locally offers the designer the ability to rapidly determine
whether or not design changes impact the product's compliance. Set-up of an open air test site and the associated calibration
is not trivial. An alternative is to use a GTEM test cell.
After the design has been completed and passes compliance testing, application will need to be made with the respective reg-
ulatory bodies for the geographic region in which the product will be operated to obtain final certifications.
C1
τ1
τ2
-----KPD KVCO
⋅
ωLBW
2N⋅
----------------------------- 1ωLBW τ2
⋅()
2
+
1ωLBW τ1
⋅()
2
+
----------------------------------------⋅⋅=
C2C1
τ2
τ1
-----1–
⎝⎠
⎛⎞
⋅=
R2
τ2
C2
------
=
mmmmmmm
12 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
RF2516 Typical Applications
FCC Part 15.231 Periodic Transmitter - 315MHz Automotive Keyless Entry Transmitter
The following information is taken or paraphrased from the Code of Federal Regulations Title 47, Part 15, Section 231 (47 CFR
15.231). Part 15 discusses radio frequency devices and section 231 discusses periodic transmissions. Please refer to the reg-
ulation itself as the final authority. Additional information may be found on the Internet at www.fcc.gov.
To highlight the main guidelines outlined by this section, there are five main limitations: operating frequency, transmission con-
tent, transmission duration, emission bandwidth, and spurious emissions.
Part 15.231 allows operation in two bands: 40.66MHz to 40.70MHz and above 70MHz. Transmission is limited to control sig-
nals such as alarm systems, door openers, remote switches, etc. Radio control of toys is not permitted, nor is continuous trans-
mission such as voice or video. Data transmission other than a recognition code is not permitted. Transmission time is limited
to 5 seconds (paragraph a) or for 1 second with greater than ten seconds off (paragraph e).
Emission bandwidth between 70MHz and 900MHz can not be more than 0.25% of the center frequency. Above 900MHz, the
emission bandwidth cannot be greater than 0.50% of the center frequency. The emission bandwidth is determined from the
points that are 20dB down from the modulated carrier. This corresponds to an occupied bandwidth of 4.5MHz at a center fre-
quency of 902MHz, 1.1MHz at 433MHz, and 788kHz at 315MHz.
Spurious emissions limits are listed in tabular form for various frequency ranges in the Section 231. Above 470MHz with a
manually activated transmitter, the fundamental field strength at a distance of 3 meters shall not exceed
12,500microvolts/meter. The spurious emissions shall not exceed 1,250microvolt/meter at a distance of 3meters above
470MHz. Refer to Appendix A for a method of converting field strength to power.
In the frequency range of 260MHz to 470MHz, one needs to linearly interpolate the maximum emissions level for both the fun-
damental and spurious emissions. The equation for this line is given by:
This equation is derived from the endpoints of the frequency range and their respective field strengths. Note that the field
strength is in microvolts per meter and the frequency is in megahertz. To determine the spurious level, divide the level calcu-
lated above for the spurious frequency by ten.
As an example, assume the fundamental is 315MHz and the reference frequency is 9.8 MHz. The field strengths of the funda-
mental, the reference spurs, and the harmonics of the fundamental up through the tenth harmonic are calculated in the follow-
ing table The occupied bandwidth limit is 787.5kHz. As shown in Table A, the fifth, seventh, and ninth harmonics fall into
restricted bands as called out in section 15.205. The limits for these restricted bands are called out in section 15.209. The
power level in the last column is the level if the output is connected directly to a spectrum analyzer. Refer to Appendix A as to
how this column was calculated.
Local Oscillator Source
Since the RF2516 has a phase-locked VCO, it can be used as a signal source. The device is an ASK/OOK transmitter, with the
data provided at the MOD IN pin. When the MOD IN is a high logic level, the carrier is transmitted. When MOD IN is a low logic
level, then the carrier is not transmitted. Therefore, to use the RF2516 as signal source, simply tie the MOD IN pin to the supply
voltage, through a suitable series resistor (minimum 3kΩ).
EμV
m
------- 412
3
---FreqMHz 70831
3
---
–⋅=
mmmmmmm
13 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Conclusions
The RF2516 is an AM/OOK VHF/UHF transmitter that features a phase-locked output. This device is suitable for use in a CFR
Part 15.231 compliant product as well as a local oscillator signal source. Two examples showing these applications were dis-
cussed.
The RF2516 is packaged in a low-cost plastic package and requires few external parts, thus making it suitable for low-cost
designs.
Table A
Frequency
(MHz)
15.205 Limits
(μV/m@3m)
15.231 Limits
(μV/m@3m)
Final FCC Mask
(μV/m@3m)
Final FCC Mask
(μV/m@3m)
Power Level
(dBm, 50Ω)
Ref Spur 305.2 - 604.17 604.17 55.62 -39.61
1 315.0 - 6041.67 6041.67 75.62 -19.61
Ref Spur 324.8 - 604.17 604.17 55.62 -39.61
2 630.0 - 604.17 604.17 55.62 -39.61
3 945.0 - 604.17 604.17 55.62 -39.61
4 1260.0 - 604.17 604.17 55.62 -39.61
5 1575.0 500 - 500.00 53.98 -41.25
6 1890.0 - 604.17 604.17 55.62 -39.61
7 2205.0 500 - 500.00 53.98 -41.25
8 2520.0 - 604.17 604.17 55.62 -39.61
9 2835.0 500 - 500.00 53.98 -41.25
10 3150.0 - 604.17 604.17 55.62 -39.61
RFMD W mm: mm 33333333 CCCCCCCC 3
14 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Pin Out
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
DIV CTRL
LD FLT
LOOP FLT
RESNTR+
RESNTR-
VREFP
GND2
VCC2
OSC B
OSC E
PD
GND
TX OUT
GND1
VCC1
MOD IN
mmmmmmm
15 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Application Schematic
315MHz
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
68 pF
9.83 MHz
33pF
*Not populated on standard Evaluation Board.
OSC B
OSC E
GND
TX OUT
GND1
VCC1
MOD IN
DIV CTRL
LD FLT
LOOP FLT
RESNTR+
RESNTR-
VREFP
GND2
VCC2
50
Ω
μ
strip
4 pF
50
Ω
μ
strip
56 nH
16 k
Ω
J1
TX OUT
220 pF
10
Ω
TX VCC
100 pF
MOD IN
S1
CAS-120B
10
Ω
82 nH
82 nH 2 k
Ω
10 nF
4.3 k
Ω
2.2 nF
1 nF
V
C
C
V
C
C
V
C
C
PD
“—4 mmmmmmm
16 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Application Schematic
315MHz
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
68 pF
9.83 MHz
33pF
OSC B
OSC E
GND
TX OUT
GND1
VCC1
MOD IN
DIV CTRL
LD FLT
LOOP FLT
RESNTR+
RESNTR-
VREFP
GND2
VCC2
50
Ω
μ
strip
4 pF
50
Ω
μ
strip
56 nH
16 k
Ω
J1
TX OUT
220 pF
10
Ω
TX VCC
100 pF
S1
CAS-120B
10
Ω
82 nH
82 nH 2 k
Ω
10 nF
4.3 k
Ω
2.2 nF
1 nF
PD
D1
SMV1249-011
150 k
Ω
AUDIO
V
CC
V
CC
RF2516 Audio Transmitter
V
CC
V
CC
RFMD mm
17 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Application Schematic
433MHz
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
68 pF
13.57734 MHz
PWR DWN 4.3 k
Ω
220 pF
220 pF 10 nF
220 pF
DIV CTR
10 nF
TX OUT
33pF
1 nF
2.2 nF
39 nH
2 k
Ω
10
Ω
10 nF
*Not populated on standard Evaluation Board.
*
2.8
V
CC
(V) Mod. in Res. Value
(R5) I
CC
(mA) P
OUT
(dBm)
1k
3k
5k
7k
9k
11k
13k
15k
17k
19k
21k
17.38
10.51
8.68
7.82
7.18
6.75
6.45
6.18
5.99
5.80
5.66
7.45
8.78
7.23
6.00
4.73
3.81
2.98
2.30
1.63
1.00
0.35
2.0
V
CC
(V) Mod. in Res. Value
(R5)
1k
3k
5k
7k
9k
11k
13k
15k
17k
19k
21k
I
CC
(mA)
11.08
10.83
4.61
4.00
3.63
3.42
3.26
3.15
3.07
3.01
2.95
P
OUT
(dBm)
-6.23
-4.40
-5.61
-6.66
-8.08
-8.93
-10.04
-10.71
-11.58
-12.32
-13.10
2.4
V
CC
(V) Mod. in Res. Value
(R5)
1k
3k
5k
7k
9k
11k
13k
15k
17k
19k
21k
I
CC
(mA)
14.05
9.00
7.48
6.73
6.16
5.79
5.53
5.29
5.13
4.98
4.86
P
OUT
(dBm)
7.94
7.63
5.95
4.64
3.35
2.40
1.47
0.75
0.05
-0.60
-1.26
3.2
V
CC
(V) Mod. in Res. Value
(R5)
1k
3k
5k
7k
9k
11k
13k
15k
17k
19k
21k
P
OUT
(dBm)
6.77
9.70
8.30
7.11
5.91
5.02
4.16
3.51
2.89
2.26
1.66
I
CC
(mA)
20.90
12.12
9.66
8.95
8.23
7.75
7.42
7.10
6.89
6.68
6.52
3.6
V
CC
(V) Mod. in Res. Value
(R5)
1k
3k
5k
7k
9k
11k
13k
15k
17k
19k
21k
P
OUT
(dBm)
5.78
10.42
9.18
8.08
6.88
6.02
5.19
4.52
3.93
3.35
2.72
I
CC
(mA)
24.68
13.88
10.94
10.14
9.34
8.81
8.44
8.09
7.86
7.63
7.44
OSC B
OSC E
GND
TX OUT
GND1
VCC1
MOD IN
DIV CTRL
LD FLT
LOOP FLT
RESNTR+
RESNTR-
VREFP
GND2
VCC2
50
Ω
μ
strip
4 pF
50
Ω
μ
strip
68 nH
2 pF
50
Ω
μ
strip
15 pF 10 nH 15 pF10 nH
22 nH
220 pF10 nF
220 pF10 nF
10
Ω
3 k
Ω
10 nF
MOD IN
39 nH
V
CC
V
CC
V
CC
PD
“EU I LE M 5—K 7 M o—«Wfi mmmmmmm
18 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Evaluation Board Schematic
315MHz
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
C8
68 pF
Y1
9.83 MHz
C7
33pF
*Not populated on standard Evaluation Board.
OSC B
OSC E
GND
TX OUT
GND1
VCC1
MOD IN
DIV CTRL
LD FLT
LOOP FLT
RESNTR+
RESNTR-
VREFP
GND2
VCC2
50
Ω
μ
strip
C6
4 pF
50
Ω
μ
strip
L3
56 nH
R4
16 k
Ω
J1
TX OUT
C5
220 pF
TX VCC
C4
100 pF
MOD IN
S1
CAS-120B
R2
10
Ω
L2
82 nH
L1
82 nH R1
2 k
Ω
C1
1
μ
F
R3
4.3 k
Ω
C2
2.2 nF
C3
1 nF
VCC
VCC
VCC
GND
P1-1 VCC1
P1-3 MOD IN
P1
1
2
3
CON3 B1
LITH BATT
VCC
+
-
2516400, rev A
PD
R5
10
Ω
RFMD mm
19 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Evaluation Board Schematic
433MHz
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
C2
68 pF
X1
13.57734 MHz
PWR DWN
R2
4.3k
Ω
C7
220 pF
C9
220 pF C10
10 nF
VCC
C12
220 pF
DIV CTRL
C11
10 nF
C1
33pF
C6
1 nF
C8
2.2 nF
L2
39 nH
R4
2k
Ω
R3
10
Ω
C13
10 nF
*Not populated on standard Evaluation Board.
C17* OSC B
OSC E
GND
TX OUT
GND1
VCC1
MOD IN
DIV CTRL
LD FLT
LOOP FLT
RESNTR+
RESNTR-
VREFP
GND2
VCC2
50
Ω
μ
strip
C3
4 pF
50
Ω
μ
strip
L4
68 nH
C15
2 pF
50
Ω
μ
strip
C14
15 pF L3
10 nH C16
15 pF
L5
10 nH
L6
22 nH
C18
220 pF
C19
10 nF
VCC
C5
220 pF
C4
10 nF
R1
10
Ω
VCC
R5
3k
Ω
C20
10 nF
L1
39 nH
J1
TX OUT
J2
MOD IN
P1
1
2
3
CON3
VCC
NC
GND
P2
1
2
3
CON3
DIV CTRL
GND
PWR DWN
PD
mmmmmmm
20 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Evaluation Board Layout (315MHz)
Board Size 1.285” x 1.018”
Board Thickness 0.062”, Board Material FR-4
RFMD mm mm (um V 7‘ km 1/ x1 \':p2 E E 3” U "\ /- w n E E1 p1 Umgln DSUP L1 R4 1‘6 N 9 NA: 4 [E % :02 GND |:|\ C13 R3l:l ]C|4:I C5 Rll:| UEC 2516411(-) 12 433MHz pcaa
21 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Evaluation Board Layout (433MHz)
Board Size 1.392” x 0.813”
Board Thickness 0.062”, Board Material FR-4
a: m 1 we own RFMD W mm: mm mm A m a; w: xv ' m»: A ma w: m as" N m a 755.3»: as m w m m m as 751.70 as 3; Wm NUY w 3;: NEXY w New new R mm; m m w: mm mm m W 1.3m m RES Eu 1.fi M1 vw 1M1 n msrc Y RES w m kHz vau m w: 5w 3mm msrc Y my“-.. - "Ohm-3k 35vpmuumulnnnm u + a: o E ‘9‘) -o- \ 5“ L \ , A“ fan e0 , \ we ‘a
22 of 22
RF2516
Rev A17 DS060712
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
433MHz Phase Noise
0
1.0 1.0-1.0
10.0
10.0
-10.0
5.0
5.0
-5.0
2.0
2.0
-2.0
3.0
3.0
-3.0
4.0
4.0
-4.0
0.2
0.2
-0.2
0.4
0.4
-0.4
0.6
0.6
-0.6
0.8
0.8
-0.8
RF2516 Output Z
Swp Max
1GHz
Swp Min
0.1GHz
VCC = 3 V
VCC = 2 V
VCC = 3.3 V
1.0 GHz 0.1 GHz