CMOS combined feedforward/feedback AGC circuit for VHF applications

This paper presents an automatic gain control (AGC) circuit targeting 250 MHz IF applications based on a combined control loop: a fast settling feedforward loop performs coarse gain adjustment, while a conventional feedback loop realizes final fine gain tuning. The AGC consists of a low-voltage broadband CMOS programmable gain amplifier and the loops are implemented making use of novel peak detection methods and other simple circuitry. The complete AGC has been designed in a standard 0.35 μm CMOS technology with 1.8 V supply voltage and exhibits a total current consumption below 1.22 mA. Measurements offer a settling-time below 0.8 μs and a 12 dB gain adjustment with an error <;±1 dB.