A 64-Gb/s PAM-4 Optical Receiver with Amplitude/Phase Correction and Threshold Voltage/Data Level Calibration

We present a 64-Gb/s four-level pulse amplitude modulation (PAM-4) optical receiver with the amplitude/phase correction and the threshold voltage/data level calibration, utilizing an inverter-based transimpedance amplifier (TIA). A variable gain amplifier (VGA) with the amplitude/phase correction is also presented. The threshold voltage of the data slicers and the data levels for the error slicers are calibrated. A three-tap decision feedback equalizer is utilized to compensate for the intersymbol interference. The tap coefficients are calibrated by using the sign-sign least-mean-square algorithm. This PAM-4 optical receiver is fabricated in a 40-nm CMOS process. For the TIA with five VGAs, the measured maximum amplitude imbalance is less than 0.4 dB and the phase imbalance is less than ±1°. Its power is 420 mW from a supply of 1.1 V excluding the output buffers. Its core area is 2.2 mm2. ? 1993-2012 IEEE.