A 3-V power supply, decades-tunable range OTA and its applications in analog signal processing

Using a simple voltage subtracter combined with cross coupled differential pairs, a low power supply, wide tunable range, high linearity transconductor is designed. The channel modulation effect of transistors is examined and cancelled by a cross biased transistor pair. A common mode feedback scheme is presented. Due to the high linear tunability, the newly designed transconductor also works as a current mode multiplier. Simulation results show that the power supply voltage can be as low as 3 V or less. The linear tunable range is more than 2 decades, dynamic range is about 70 dB and cut-off frequency is 10 MHz. The design trade-off between linear input and tunable range is described. The maximum differential input voltage that the device can handle is 1.2 V. Owing to high programmability, the transconductor presented here can be implemented for various applications. Finally, a second order lowpass filter is built whose passband can be tuned from 10 kHz to 1.6 MHz.