further support the SDR. a CDMA signal has between 10 and 12 dB of peak to rms on the envelope. A CDMA signal of -40 dBm thus actually peaks very close to -30 dBm. Therefore, both Case study: A close look at standards require about the same peak signal capacity. a CDMA2000 and UMTS SDR Since we know that we will need to digitize the sig- receiver nals, initial ADC characteristics may be established. Later in the analysis, the specification can be validated to Now that many of the facets of SDR have been determine if the assumptions were correct. Since high- discussed, the final section will cover an example of performance data converters are expensive, it is desirable a multi-carrier SDR receiver. Although this is not a full to use the lowest performance possible that allows the analysis, it will cover many of the issues that surround the specifications to be met. In typical converter specifica- design and development of an SDR that are not covered tions [19], the fullscale input range is 2 volts peak to peak differential. If this input is terminated with 200 ohms in a typical receiver design. As with any design, the first differentially, the rms power to drive the converter to place to start is with the specifications. The following fullscale will be +4 dBm. Similarly, the converter SNR is table summarizes a few of the critical specifications for 75 dB and the SFDR, both single and two-tone, is -95 both CDMA2000 and UMTS (WCDMA). dBFS. This performance is maintained out to analog frequencies of 100 MHz providing flat performance. CDMA2000 From this information an initial estimate of the con- version gain required can be determined using Equation Reference sensitivity -117 dBm -121 dBm (2.3.1): Bandwidth 1.25 MHz 5 MHz Chip rate 1.2288 MCPS 3.84 MCPS Gmax = PADC_Fullscale P max_signal = = 44-(-30) Signal spectral -177.9 dBm/Hz -186.8 dBm/Hz = 34 dB density In order that the receiver not be overdriven, the Sample rate 61.44 MSPS 61.44 MSPS conversion gain will be limited to 30 dB. For the moment, 50 oversample 16 