A 10-Gb/s inductorless AGC amplifier with 45-dB linear variable gain control in 0.13-µm CMOS

This paper presents an inductorless, 10Gbps automatic gain control (AGC) circuit including a speed enhanced variable gain amplifier (VGA), a power detector, a comparator and a switching exponential function generator for extended dB-linear performance. Third order interleaved feedback technique is utilized to enhance the speed of the current steering VGA stage. A stagger-tuned switching architecture for CMOS exponential function generation is utilized to achieve a dB-linear gain control range of 45dB with better than ±0.5 dB gain error. The AGC circuit achieves a maximum data rate of 10 Gbps for 2³¹-1 PRBS input, maintaining 360mV_p-p constant differential output with a BER <; 10^-12 for an input dynamic range of ~24 dB (15mV_p-p to 240mV_p-p). Fabricated in IBM 0.13-μm CMOS technology, the chip draws 50 mW from a 1.2 V power supply (excluding output buffer) and occupies an active area of 0.4 mm².