2.4 GHZ TRANSMITTER AND RECEIVER

Michael KleppingerRobert 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 bi-

directional 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 (RF9986)

Receive AGC and Demodulator (RF2667)VCO/High – Isolation Buffer Amplifier (RF2504)

On TX side: 2.5 GHz Direct Quadrature Modulator (RF2422)

Medium Power Linear Amplifier (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 FUNCTION HARDWARE DESCRIPTION1 NC 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 FUNCTION HARDWARE DESCRIPTION1 VCC1 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 GND Direct connection to ground7 GND Direct connection to ground8 FM IN + 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 GND Direct connection to ground18 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.

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 GND Direct connection to ground21 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

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 FUNCTION DESCRIPTION1 I REF 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) 3-

Channel 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 micro-

strip. 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.