Design of a 50MHz Bandwidth TIA Using Negative Capacitance

The transimpedance amplifier (TIA) is a key component in the analog baseband (BB) of a current-mode receiver (RX). It requires low input impedance (Z
in
) and high linearity up to very high frequencies. However, due to the narrow bandwidth (BW) of the Miller-compensated transconductance amplifier (OTA), Z
in
often peaks at medium frequency (MF), degrading out-of-band (OOB) linearity. This article aims to remove the peak. To this end, an OTA with 44.8dB open-loop gain and 1.8GHz unity-gain loop bandwidth (UGLB) is proposed. It’s based on a two-stage pseudo-differential OTA. Instead of the Miller compensation, which pushes the dominant pole to lower frequency, this paper uses negative capacitance (NC) to push the non-dominant pole to higher frequency, thereby increasing UGLB and phase margin (PM). The TIA, designed and simulated in the TSMC 40nmLP technology, achieves 50MHz BW for 5G sub6GHz wideband RX. Its in-band (IB) and OOB IIP3s are 35.4dBm and 45.2dBm, respectively. Z
in
is less than 11.4Ω at all frequencies, while consuming 9.4mW from a 1.2V supply.