Modulation in Software

Generating Universal Product Code version A in Software Modulation

Virtually all high-speed digital communication systems will employ a predesigned modem (modulator-demodulator) for the task of modulating and demodulating the digital signal stream through the wireless system Still, a methodology for the design of a modulator/demodulator is included in this section to assist in the construction of lower-speed systems that may not have a separate modem

A popular chip that can perform both modulation and demodulation is the RFMD RF2703; with a few component changes, it can be adopted as a modulator (Fig 240) or as a demodulator (Fig 241) The RF2703 is a monolithic IC that can operate with an IF from 100 kHz to 250 MHz, and with a VCC of 3 to 6 V In the modulator configuration, pins 1 and 3 are the single-ended I and Q inputs (they can be driven differentially, while 2 and 4 are at RF ground) Since pins 1 and 3 are at a high input impedance, 51-ohm resistors are added for 50ohm matching, while the capacitors, at less than 1-ohm Xc, supply DC blocking Pin 5 is at RF ground through a 01- F capacitor In normal modulator operation, pins 8 and 9 are left floating, while pins 10, 11, and 12 are connected directly to the ground plane Pin 13 is a high-impedance input, so a 51-ohm resistor can be placed in shunt to match to the 50-ohm LO signal input A low power LO with medium-voltage outputs (01 to 1 VPP) is required, as is a LO that is at twice the desired frequency of the carrier (this is because an internal divide-by-2 frequency divider is used for the 90 degree splitter; or LO 2 IF) Pin 14 supplies DC power to the chip and must be adequately bypassed Pin 6 should be tied to pin 7, while VCC is connected through a 1200ohm resistor, or an inductor, to bias the internal active mixers However, since

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Downloaded from Digital Engineering Library @ McGraw-Hill (wwwdigitalengineeringlibrarycom) Copyright 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website

the signal output at pin 6/7 is at 1200 ohms, either a high input impedance filter should be used, or LC matching should be performed to obtain an impedance match for maximum gain When the RF2703 is in demodulator configuration, pin 1 with pin 3 tied to it has the IF injected into the high input impedance, which is shunted by 51 ohms for matching Pins 2 and 4 are connected together and placed at RF ground Pin 5 is at RF ground through the 01- F capacitor, while pins 6 and 7 are tied to VCC to bias the internal active mixers Pins 8 and 9 are Q and I out, with 50-ohm outputs (but can drive only a high-impedance load and are not internally DC blocked) Pins 10, 11, and 12 are sent directly to ground Pin

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13 is the high-impedance LO input, with 51 ohms shunted to ground for a 50ohm oscillator Pin 14 is VCC, which must be adequately bypassed 26 Digital Test and Measurement

This section describes new tests created to confirm proper radio operation with digital modulations by measuring BER and generating constellation and eye diagrams, as well as the more rigorous testing methods necessary to detect the smaller levels of error-producing phase noise, frequency instabilities, group delay variations, etc, found in today s high-end digital radios And since digital power measurement is not the same as for the narrowband analog modulations, techniques for its accurate measurement will be presented, as will a few of the more important testing procedures for QAM and QPSK wireless devices

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