0.3 V tunable OTA and Gm-C filter in 0.13 μm CMOS

Abstract

This study presents an ultra-low-voltage Operational Transconductance Amplifier (OTA) and Gm-C filter, both operating with a single supply voltage of 0.3 V. Using the pseudo-differential structure, the common mode rejection is the main challenge in the low-voltage condition and it is resolved by a new common mode feedback circuit. OTA can be tuned through the gate terminal of body-driven PMOS input transistors. Postlayout simulation showed 23.4 dB differential gain and 47.4 dB CMRR at low frequencies. By changing the tune voltage from 50 mV to 0 V, the transconductance of OTA could be tuned from 7.9 to 17.4 μA/V. By applying input voltages up to 0.36 Vpp, the Total Harmonic Distortion (THD) of the output current remained less than {60 dB. The proposed OTA was employed to implement a tunable low-pass Gm-C filter. The cut-off frequency of Gm-C filter could be tuned from 1.13 to 1.9 MHz, making it applicable to multi-standard direct conversion receivers as the channel selection filter. According to the results of postlayout simulations, the power consumption of the filter and its input-referred voltage noise were 111.3 μW and 168.7 nV/√Hz, respectively. The post-layout simulation showed the IIP3 with 8.5 dBm at a cutoff frequency of 1.9 MHz.