A cellular analog front end with a 98 dB IF receiver

To date, mixed-signal CMOS devices designed for cellular telephony have adopted conventional receiver architectures. They consist of dual baseband A/D converters with performance limited to approximately 60 to 75 dB dynamic range. Thus, these architectures require the following components in the preceding IF strip. Since the overall system dynamic range is on the order of 140 dB, a large amount of programmable gain (80-100 dB) is required in the preceding RF/IF strip to preserve the system noise. External filters at both the first and second IF frequencies are required to provide full channel selectivity before the A/D conversion is performed. Also, dual analog quadrature mixers are required to convert the receive signal from the second IF to baseband. The mixed-signal CMOS device presented in this paper substantially reduces the programmable gain, filtering, and external components required in the IF strip. This is accomplished by performing an IF A/D conversion and providing 98 dB dynamic range.<>