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 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 DESCRIPTION 1 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 Logic high (>3.1V) turns amplifier on. Pin connected to EN 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 Matched to 50 ohm. Connected to SMA connector through OUT 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 DESCRIPTION 1 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 ground 7 GND Direct connection to ground 8 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 ground 18 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 ground 21 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 DESCRIPTION 1 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.
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