2.4 GHZ TRANSMITTER AND RECEIVER
Michael Kleppinger
Robert Barrington
ECE 4040
INTRODUCTION
The following proposed design is a general purpose 2.4 GHz radio frequency transmitter
and receiver system operating in the ISM band. Eventually, this design will be incorporated into
the Wideband RF / OE Video Link being developed by Lawrence Carastro and Dr. Martin
Brooke. Currently, the Video Link is designed to receive an analog NTSC video signal from a
color CCD camera and convert it to a D1 video signal. The digital video signal is then transmitted
through either a RF or an Optical link across a room. On the receiving end, the video signal is
converted from digital D1, back to analog NTSC and displayed on a monitor. Originally, in Phase
1, the video link was constructed using commercial, off the shelf products with minimal design
involved. Now, in Phase 2 of the Video Link development, this general purpose 2.4 GHz system
is designed to replace the off the shelf wireless A/V transmitter which was used in the original
system.
STANDARDS
As background for this design, certain sets of standards were researched in order to
determine feasibility and to establish design parameters. First off, it was important to find the
Federal Communication Commission (FCC) regulations covering the frequency range involved
(2.4 to 2.5 GHz) to make sure it could be used for this application. The second set of standards
involves the MPEG video compression that is used to compress the NTSC video from the camera.
The MPEG standards are used to determine the maximum bitrates that may be required to transfer
the video data.
FCC Regulations
Our system is regulated under Part 15 of the Federal Communications Commission
(FCC) for Legal Unlicensed Transmitting on the ISM Band. The frequency that pertains to our
general system is 2400 – 2483.5 MHz, and is used for Industry, Scientific research, and Medical
equipment. Part 15 of the FCC applies strict regulations on how the ISM Band is utilized. For
our purpose, the maximum field strength of the fundamental frequency is given as 50mV/m. So,
instead of a declared maximum output power level, we are given a maximum field strength limit
that we must abide by. Most of the time, calculations must be made by working back from the
maximum field strength limit, and using that value to determine the amount of power output
required. Since the power output tends to be small, most companies comply to the regulation by
using higher output power and a less effective antenna. More information on FCC regulations,
including some calculations, is available in the appendix.
MPEG Compression
MPEG-2, which stands for Moving Pictures Expert Group - Level 2, is an internationally
adopted standard for compressing full screen full motion video which reaches compression ratios
from 8:1 up to 30:1. MPEG compression uses a layered coding structure which lowers the amount
of video data needed through motion compensation and spatial redundancy. The standards for
MPEG are outlined in the International Standard Organization document ISO 13818. There are
different standard sizes for encoding NTSC video, however the one chosen for this system is
CCIR 601 video, also known as Main Level or Full D1. The frame size for this standard is 720 x
480 pixels/frame, with a frame rate of 30 frames/second (~10.4 M pixels/second). The rate of
transmission for Full D1 can range from 1 up to 15 Mbps, depending on the amount of
compression available. More information about MPEG compression can be found in the MPEG
FAQ in the appendix.
SYSTEM OVERVIEW
This 2.4 GHz transmitter and receiver system that was chosen is based on the bidirectional general purpose system developed by RF Micro-Devices (www.rfmd.com). The general
system incorporates five chips, all of which are available from RFMD:
The chips involved are as follows:
On RX side:
PCS Low Noise Amplifier/Mixer
Receive AGC and Demodulator
VCO/High – Isolation Buffer Amplifier
(RF9986)
(RF2667)
(RF2504)
On TX side:
2.5 GHz Direct Quadrature Modulator
Medium Power Linear Amplifier
(RF2422)
(RF 2128P)
In the prototype build of this system, each chip is to be built on a separate board along
with its associated components, with all five boards connected together using 50 ohm SMA
cables. In the general system, the RF2504 (VCO/Buffer Amp) is used in order to supply the entire
system using a single reference frequency. This particular method requires a Dual PLL (phase
locked loop) which is beyond the complexity of this phase of the design. In order to compensate,
this stage is replaced by two different external frequency sources, one connected to the AGC and
Demodulator (RF2667, Pin 12) and the other connected to the Low Noise Amplifier / Mixer (RF
9986, Pin 12). Using this simplification, the entire system can now be implemented with only
four chips, a relatively small amount of discrete parts (mostly capacitors), and a few dielectric
filters.
This document discusses the design around three of the chips: the RF9986, the RF2667,
and the RF2422 (the fourth chip, the RF 2128P, is discussed in a separate document). The
following sections will examine each chip separately, discussing chip pin out, schematic design,
and board layout. For all of the chips, the data sheets from RFMD are available in the appendix.
COMPONENTS
RF9986 - PCS Low Noise Amplifier/Mixer
The RF9986 Low Noise Amplifier/Mixer is a monolithic integrated receiver front-end
which can be used for PCS, PHS, and WLAN applications. This chip contains almost everything
that is needed to implement the RF functions of a receiver front-end. Included are a LNA (low
noise amplifier), a double balanced Gilbert cell mixer, a balanced IF (intermediate frequency)
output, a LO (local oscillator) isolation amplifier, and an LO output buffer amplifier. Because this
is a general purpose chip, passive filtering and LO generation must be implemented externally
In the overall system, this chip, along with its associated board components, receives the
RF signal from the antenna, filters and amplifies it, and passes it through to the AGC and
Demodulator (RF2667). The local oscillation (LO) signal is produced by an external frequency
source ( ~1.095 GHz). This LO signal is then passed out of the RF2667 (Pin 6) to the RF2422 in
the transmitter (Pin 6) in order to synchronize the transmitting and receiving frequencies. The
passive filtering is achieved using a Toko (www.tokoam.com) 2.450 GHz dielectric filter
(TDFSIA-2450T-11). The following table is a breakdown of the pin outs for the RF9986, as well
as a description of the associated on-board hardware: (A drawn schematic is available in the
appendix)
PIN OUT FOR RF 9986
PIN
1
FUNCTION
NC
HARDWARE DESCRIPTION
No Connect. Grounded (recommended)
2
VCC1
3.6V – 22pF bypass cap between supply and GND,
Pads available for additional 1nF cap if needed
3
VCC2
3.6V – uses same bypass cap connected to Pin 2
4
GND1
Connected to ground plane using physically short
connections
5
LNA IN
50 ohm source impedance. Connected to SMA connector
through 50 ohm micro-strip
6
GND2
Connected to ground plane using physically short
connections
7
GND3
Connected to ground plane using physically short
connections
8
NC
No Connect. Grounded (recommended)
9
GND4
Connected to ground plane using physically short
connections
10
VCC3
3.6V – 22pF bypass cap between supply and GND,
pads available for additional 1nF cap if needed
11
LO BUFF
EN
Logic high (>3.1V) turns amplifier on. Pin connected to
external source through 1k ohm resister with 22pF bypass
cap. Pads available for additional 1nF cap
12
LO IN
Matched to 50 ohm. Connected to external 1.095 GHz
frequency source through 50 ohm micro-strip
13
LO BUFF
OUT
Matched to 50 ohm. Connected to SMA connector through
50 ohm micro-strip
14
GND 5
Connected to ground plane using physically short
connections
15
IF+
Output impedance 1k. L – network used to bias output (see
NETWORK1 in appendix).
16
IF-
Output impedance 1k. L – network used to bias output (see
NETWORK1 in appendix).
17
GND6
Connected to ground plane using physically short
connections
18
MIX RF IN
Matched to 50 ohm. Pin connected to Toko filter through 50
ohm micro-strip and series 22pF cap
19
GND7
Connected to ground plane using physically short
connections
20
LNA OUT
Connected to Pin 22 through 2.7 nH bias/matching inductor,
in conjunction with a series 1.8 pF cap. The Toko filter is
connected through a 50 ohm micro-strip and a 22 pF cap
21
GND8
Connected to ground plane using physically short
connections
22
VCC4
Connected to Pin 20 through 2.7 nH inductor. DC biased
using 22 pF cap.
23
GND9
Connected to ground plane using physically short
connections
24
NC
No Connect, Grounded (recommended)
TOKO TDFISA-2450T-11 – Dielectric Filter
The only other major component on-board with the RF9986 is a Toko (www.tokoam.com)
2.4 GHz dielectric filter used for passive filtering. This filter features a center frequency (Fo) of
2450.0 MHz with a band width of Fo +/- 50 MHz. The input/output impedance of the filter is 50
ohm. In this system, the input for the filter, Pin 4, is connected to the LNA OUT (RF9986, Pin
20) though a 1.8 pF capacitor followed by a 50 ohm micro-strip. The output of the filter, Pin 2
connects to the MIX RF IN (RF9986, Pin 18), also through a 50 ohm micro-strip. Single 22 pF
capacitors are connected in series to both the input and the output pins on the filter to DC bias the
signal. The other two pins on the filter, Pin 1 and Pin 3, are connected to ground.
RF2667 - Receive AGC and Demodulator
The RF2667 is a complete integrated IF AGC Amplifier and Quadrature Demodulator
developed for the receiver of the general dual-mode system. This chip is designed to amplify
received IF signals while maintaining 100dB of gain control range. The output signal is
demodulated baseband I and Q signals. The RF2667 contains inputs for FM (Frequency
Modulation) or CDMA (Code Division, Multiple Access) signals, depending on the source. FM
uses a narrow band signal, whereas CDMA uses a wider band with multiple channel access. For
this system, the CDMA IN+ (Pin 4) is being used for the input signal from the RF9986. This
input signal is filtered on-board using a Toko 210 MHz dielectric SAW filter (SF210YE-001).
The RF9986 requires an off board LO signal (supplied to Pin 12). In the prototype system, the LO
signal is to be supplied using an independent (~370 MHz) frequency supply. In a system utilizing
the RF2504 and Dual PLL to eliminate one frequency supply, this signal is the required source
signal. The RF2504 and Dual PLL is used to convert the source to the other required frequency
(~1.09 GHz). The following table is a pin out of the chip, which includes descriptions of each
pin’s associated hardware on the schematic: (A drawn schematic is available in the appendix)
PIN OUT FOR RF2667
PIN
1
FUNCTION
VCC1
HARDWARE DESCRIPTION
2.7 V to 3.3 V. Connected in parallel to pins 2 and 3.
Bypassed using a 10 nF cap.
2
VCC2
2.7 V to 3.3 V. Connected in parallel to pins 2 and 3.
Bypassed using a 10 nF cap.
3
VCC3
2.7 V to 3.3 V. Connected in parallel to pins 2 and 3.
Bypassed using a 10 nF cap.
4
CDMA IN+
Single-ended input, balanced to 1.2k ohm. A L-network is
used to balance the pin to the Toko filter. (See NETWORK2
in appendix)
5
CDMA IN-
Not used. Connected through ground using 10 nF cap.
6
7
8
GND
GND
FM IN +
Direct connection to ground
Direct connection to ground
Not selected. Connected to ground through 10 nF cap.
9
FM IN -
Not selected. Connected to ground through 10 nF cap.
10
BG OUT
Connected to ground through 10 nF bypass cap.
11
DEC
Connected to ground through 10 nF bypass cap.
12
LO -
Connected to external frequency source through 50 ohm
micro-strip and L-network (based on source frequency used)
13
LO +
Connected to ground through 1 nF cap.
14
IN SEL
Input Select – Logic “0” selects FM
Logic “1” selects CDMA
15
Q OUT -
Connected to SMA connector through 100 nF cap and 50
ohm micro-strip. A L-network is used to balance the output
depending on the A-D converter used
16
Q OUT +
Connected to SMA connector through 100 nF cap and 50
ohm micro-strip. A L-network is used to balance the output
depending on the A-D converter used
17
18
GND
FL -
Direct connection to ground
Shunt filter of the AGC. The filter consists of a shunt
inductor (390 nH) and shunt cap. (7 pF), both connected to
VCC which is bypassed using a 10 pF cap.
19
FL +
Shunt filter of the AGC. The filter consists of a shunt
inductor (390 nH) and shunt cap. (7 pF), both connected to
VCC which is bypassed using a 10 pF cap.
20
21
GND
I OUT +
Direct connection to ground
Connected to SMA connector through 100 nF cap and 50
ohm micro-strip. A L-network is used to balance the output
depending on the A-D converter used
22
I OUT -
Connected to SMA connector through 100 nF cap and 50
ohm micro-strip. A L-network is used to balance the output
depending on the A-D converter used
23
GC
Analog Gain Control – Range .5 to 2.5 VDC. May require
separate voltage source
24
PD
Power Down Control – All circuits are active with logic
high. Connected directly to VCC
Determining IF
The Toko Filter used along with the RF2667 is based on the IF (intermediate frequency)
of the general system. The determination of this IF is based on primarily on the complete system
utilizing a RF2504 as a VCO. The RF2504 is designed to operate between 700 and 1500 MHz.
By setting V(tune) (RF2403, Pin 2) at Vcc (3.6 to 3.8 V), a VCO frequency of ~ 1104.625 MHz
is produced (refer to page12-8 of the RF2504 data sheet in the appendix). Following the general
system diagram, this frequency is then doubled to ~ 2.2095 GHz. This signal is input to the RF
9986 and mixed with the ~ 2.4 GHz signal to create an IF of ~210 MHz.
Calculation: 2.41925 GHz - 2.20925 GHz = 210 MHz
TOKO SF210YE-001 – Dielectric Filter
Also located on-board with the RF2667 is a Toko (www.tokoam.com) 210 MHz
dielectric SAW filter, used to filter the input signal from the Low Noise Amplifier / Mixer. This
filter features a center frequency (Fo) of 210.090 MHz with a pass band width of at least +/- 15
KHz at 3 dB. The load impedance is 662 ohm // -1.91 pF. In the prototype the input to the filter,
Pin 9, is connected through a 50 ohm micro-strip to a SMA connector connected to the output of
the RF 9986 board. The output of the filter is matched using a LC filter and connected to the
CDMA IN + (Pin 4) on the RF2667. (See Calculation section of appendix for matching network
calculations) The other pins on the filter, 1-3,5-8, and 10 are all grounded.
Toko No. : SF210YE-001
RF2422 - 2.5 GHz Direct Quadrature Modulator
The primary chip used in the transmit end of this dual-mode system is the RF2422, a
monolithic integrated quadrature modulator IC. The RF2422 is capable of universal direct
modulation for high frequency AM, PM, or compound carriers. Featured in the IC are differential
amplifiers for the modulation inputs, a 90-degree carrier phase shift network, carrier limiting
amplifiers, two matched double-balanced mixer, a summing amplifier, and an output RF
amplifier. Although this output RF amplifier can drive 50 ohms from 800 MHz to 2500 MHz, an
additional medium power linear amp (RF2128P) will be used between the output (Pin 9) and the
antenna to amplify the transmitted signal. The inputs required the I and Q references and signals.
The only other input to the chip is the local oscillator (LO IN) which is supplied from the
Buffered LO (Pin 13) of the RF9986.
PIN OUT FOR RF2422
PIN
1
FUNCTION
I REF
DESCRIPTION
Connected to SMA connector through 50 ohm micro-strip
2
Q REF
Connected to SMA connector through 50 ohm micro-strip
3
GND2
Connected directly to ground
4
GND2
Connected directly to ground
5
GND2
Connected directly to ground
6
LO
Connected to SMA connector through 50 ohm micro-strip
7
VCC1
5V. Bypassed to ground through 100 uF capacitor
8
PD
Power Down control. All circuits are fully functional when
pin is logic high. Connected directly to pin 7.
9
RF OUT
50 ohm output. Connected to SMA connector through 50
ohm micro-strip.
10
GND3
Connected directly to ground
11
VCC2
5V. Bypassed to ground through 100 nF cap.
12
GND1
Connected directly to ground
13
GND1
Connected directly to ground
14
GND1
Connected directly to ground
15
Q SIG
Connected to SMA connector through 50 ohm micro-strip
16
I SIG
Connected to SMA connector through 50 ohm micro-strip
DATA CONVERTERS
In order to integrate this transmit and receive system into the Wideband RF / OE Video
Link system, the input D1 video needs to be converted from a digital to an analog signal before
being transmitted. The Digital to Analog Converter (DAC) that was chosen to do the conversion
is the Intersil (www.intersil.com). The HI1178 is an 8-bit, 40MSPS (Mega Samples Per Second) 3Channel D/A converter. The output signal of the receiver also needs to be converted from an
analog signal back to a digital signal. The Analog to Digital Converter (ADC) chosen is the
HI1175, an 8-bit, 20 MSPS Flash converter also manufactured by Intersil. Although these two
converters will be necessary to integrate the transmitter and receiver into the final Video Link,
they have yet to be implemented. Two useful documents which may help in implementing these
chips are AN9845 – Understanding Current Output D/A Converters and AN9214 – Using Intersil
High Speed A/D Converters (See Data Converter section of the appendix).
BOARD LAYOUT
The overall transmit / receive system consists of four boards: the Quadrature Modulator
(RF 2422), the Power Amp (RF 2128P, not covered in this document), the Low Noise
Amp/Mixer (RF 9986), and the AGC and Demodulator (RF2667). The included board layouts
were created using the freeware version of EasyTrax. The boards are designed to utilize a single
sided layout with a solid ground plane on the opposite side. Large grounded areas on the top layer
of the board need to be connected to the ground plane by soldering a piece of wire through the
vias. All of the traces on the boards have a width of 12 mils, with the exception of the large traces
at the SMA connectors. These traces have a width of 50 mils, which serves as a 50 ohm microstrip. For discrete components, the spacing between the traces was set to approx. 75 mils (~2mm).
This distance was chosen in order to be able to allow for Type 0805 (2.0 mm) or Type 1206 (3.2
mm) size components.
SINGLE CHIP SOLUTION
RF2938 – 2.4GHz Spread Spectrum Transceiver
In future versions of the Wideband RF/OE Video Link, it may be practical to use a single
RF2938 chip from RFMD to replace the proposed system presented. The RF2938 is a single chip
transmitter / receiver, specifically designed for direct system spread spectrum systems operating
in the 2.4 GHz ISM band.
The RF2938 Single Chip Transceiver
The chip features a direct conversion from IF receiver, quadrature demodulator, I/Q baseband
amplifiers with gain control, on-chip programmable baseband filters, and dual data comparators.
A QPSK modulator and upconverter are also available for transmitting. This chip is designed to
be used as part of a 2.4 GHz chip set consisting of a LNA / MIXER (RF2444), a Power
Amplifier, and a dual frequency synthesizer. In addition, the RF2938 reuses the same SAW filter
for both the transmit and receive ends, reducing the amount of SAW filters required.
CONCLUSION
The system presented here is a general 2.4 GHz transmitter and receiver which was
designed to be used in the Wideband RF / OE Video Link. The system is based on a 2.4 GHz
general system developed by RF Micro-Designs (www.rfmd.com). In the prototype version, the
system is implemented using three boards, one for each chip involved: the RF 9986, the RF 2667,
and the RF 2422. These three boards are designed to be produced separately and connected using
50 ohm SMA cables. Currently in the project, schematics have been developed and all three
boards have been drawn using EasyTrax. Due to time constraints, the actual production was never
completed. At this point, the Gerber files of the boards need to be etched and assembled. After
assembly, testing needs to be done in order to finalize the values of the discrete components.
Currently, all of the chips have been ordered, but orders still need to be made for the Toko Filters
and the discrete components when values are finalized. All associated schematics, board layouts,
and data sheets can be found in the appendix section.