On the Design of Linearly Tunable Wide Input Voltage Range CMOS OTA and Its Application

In this paper, a CMOS OTA with a wide input voltage range and linearly tunable transconductance gain (gm) is presented. To achieve the linear control of transconductance, the bias current (IB) is squared by using the current squarer circuit before applying it into the main CMOS OTA. In addition, the source degeneration technique is used to extend the input voltage range. The frequency response of the proposed OTA is analyzed and studied. The performances of the proposed CMOS OTA are tested on PSPICE simulation on TSMC 0.35 μm CMOS technology with a power supply of ±1.5V. The transconductance of OTA can be linearly tuned by adjusting IB in the range from 1nA to 1.1mA. The proposed OTA also operates well in a wide input voltage range from -1 to 1 volt with a good linearity, and a bandwidth of approximately 8.35 GHz can be achieved. Moreover, a linearly controlled quadrature oscillator based on the proposed CMOS OTA is present to demonstrated the linearly tunable transconductance gain.