A Continuous-Time Linear Equalizer With Ultrafine Gain Adjustment Achieving 0.3-dB DC-Gain Step and 0.9-dB Peaking-Gain Step

A four-stage continuous-time linear equalizer (CTLE) in a 28-nm CMOS process is presented. The proposed CTLE provides peaking gain at a Nyquist frequency of ∼16 GHz, as well as mid-frequency boosting for low-frequency channel-loss compensation. An ultrafine gain-tuning scheme employing an extra positive-feedback path is proposed and analyzed, which enables both a large gain-tuning range and fine gain-tuning steps. The dc gain covers a wide range from −3.81 to 11.29 dB with a step size of less than 0.3 dB, and the peaking gain at Nyquist frequency can be adjusted from −3.52 to 13.48 dB with a step size of less than 0.9 dB, while providing a large boost range of 13 dB. The CTLE consumes 32-mW power from a 0.9-V supply.