A Tunable Pseudo-Differential OTA With $-78~{\hbox {dB}}$ THD Consuming 1.25 mW

A novel linear tunable transconductor based on a combination of linearization techniques is presented. The input signal is transferred to the V-I conversion element by means of a high-speed feedback loop. Then, the linear V-I conversion is accomplished using quasi-floating-gate MOS transistors biased in the triode region. Finally, the absence of current mirrors in the signal path provides low sensitivity to transistor mismatch and reduces the harmonic distortion. The operational transconductance amplifier (OTA) was fabricated in a 0.5-mum CMOS technology with a single 3.3-V supply voltage. Experimental results show a total harmonic distortion of -78 dB at 1 MHz with 1-V_pp input signal. High linearity of the OTA is obtained over a two octave tuning range with only 1.25-mW power consumption.