A 10 Gb/s Inductorless AGC Amplifier With 40 dB Linear Variable Gain Control in 0.13 $\upmu \text{m}$ CMOS

This work presents an inductorless, 10 Gbps automatic gain control (AGC) circuit including a speed enhanced variable gain amplifier (VGA), a power detector, a comparator, and a novel exponential function generator for extended dBlinear performance. Third-order interleaved feedback technique is utilized in the current steering VGA stage to achieve 10 Gb/s operation without using on-chip inductors. A stagger-tuned switching architecture for CMOS exponential function generation is proposed to achieve a dB-linear gain control range of ~40 dB with better than ±1 dB gain error. The relationship between tuning range and approximation error is analyzed and a novel current ratio generator circuit is proposed to implement the approximation functions in the current domain. The AGC circuit achieves a highest data rate of 10 Gb/s for 231-1 PRBS input, maintaining 360 mVp-p constant differential output with a BER <;10-12 for an input dynamic range of ~24 dB (15-240 mVp-p). Fabricated in IBM 0.13 μm CMOS technology, the chip draws 50 mW from a 1.2 V power supply (excluding the output buffer) and occupies an active area of 0.4 mm
²
.