Ultra low voltage, high performance operational transconductance amplifier and its application in a tunable Gm-C filter

This paper presents an ultra low voltage, high performance Operational Transconductance Amplifier (OTA) and its application to implement a tunable Gm-C filter. The proposed OTA uses a 0.5 V single supply and consumes 60 μw. Employing special CMFF and CMFB circuits has improved CMRR to 138 dB in DC. Using bulk driven input stage results in higher linearity such that by applying a 500 mv_p-p sine wave input signal at 2 MHz frequency in unity gain closed loop configuration, third harmonic distortion for output voltage is −46 dB and becomes −42.4 dB in open loop state for 820 mv_p-p output voltage at 2 MHz. DC gain of the OTA is 47 dB and its unity gain bandwidth is 17.8 MHz with 20 pF capacitance load due to both deliberately optimized design and special frequency compensation technique. The OTA has been used to realize a wide tunable Gm-C low-pass filter whose cutoff frequency is tunable from 1.4 to 6 MHz. Proposed OTA and filter have been simulated in 0.18 μm TSMC CMOS technology with Hspice. Monte Carlo and temperature dependent simulation results are included to forecast the mismatch and temperature effects after fabrication process.