A single-chip CMOS analog front-end for high-speed modems

A single-chip analog front-end for high-speed modems has been developed in 5μ polysilicon CMOS process. The chip contains a 10-bit A/D and an 8-bit D/A converters, a novel 128-step 0.375 dB/step programmable gain stage, 20-step 1dB/step programmable attenuator, switched-capacitor and active RC low-pass and high-pass filters for the receive and transmit directions, and all the associated TTL level compatible control logic. A CMOS band-gap voltage reference is shared between the receiver and transmitter. The chip, housed in 40-pin plastic package, is 223×219 mil2 and dissipates 120 mW using ±5V supplies.

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