X oversample assuming that the noise figure of the front end, less Despread and coding 21 dB 25 dB the ADC, will be 3 dB, the thermal noise delivered to the ADC can be determined. At room temperature, the Narrowband blocker thermal noise can be calculated to be -30 dBm CDMA blocker -52 dBm -40 dBm NSDAFE = Two-tone blocking -45 dBm, -48 dBm, 1 CW 2 tone CW and 1 CDMA + G + NFAFE = -174 dBm/Hz + 30 + 3 The goal of this exercise will be to design a multi- = -141 dBm/Hz carrier, multimode, single-band receiver RF through Based on this information, the NSD of the ADC can baseband that is capable of processing both of these be determined using Equation (2.3.8): standards either independently or at the same time. Such a design would be useful for manufacturers of 3G base NSD = PADC_Fullscale - ADC_Fullscale station equipment where it is desirable to have a single piece of hardware that is capable of processing both - 10 log Sample_Rate = 4 dBm - 75 dB standards, thereby eliminating duplicated design efforts. One of the most direct ways of accomplishing this is to compare the two specifications and determine which 10 log(61.44MH2) -145.9 dBm/Hz will limit performance. One of the first issues will be to determine the largest signal that requires processing. The Since the NSD of the ADC is less than 10 dB better CDMA2000 standard calls for a -30 dBm narrowband than the NSD of the AFE, the noise contributed from the signal, whereas UMTS does not address narrowband ADC must be included in the overall noise analysis. blockers. However, it does require that a -40 dBm Therefore, using Equation (2.3.10) will provide the CDMA signal be correctly processed. While narrowband equivalent NF of the ADC for the configuration used here. Software defined radio CHAPTER 2.3 NFADC = PADC_Fullscale SNRADC_Fullscale these updated terms in the equation above for the overall NSD, the total noise can now be determined. - 10 0 log (Sample-Rate) NSDAFE = NFAFE -10108(kxtx1H -174 dBm/Hz + 30 + 4.13 61.44 MSPS 4 dBm - 75 - -139.87 dBm/Hz If this en