A 30 pA/V–25μA/V linear CMOS channel-length-modulation OTA

A fully balanced highly linear CMOS operational transconductance amplifier (OTA) is presented. The proposed circuit combines a cross-coupled channel length modulation cell with a tunable-gain current mirror. Good linearity over a wide tuning range is achieved. As an example, the OTA has been used in designing a second-order tunable VCO. Both the OTA and the VCO have been fabricated in the AMS 0.35μm CMOS process. Measured results show that the transconductance of the OTA ranges from 30 pA/V to 25μA/V, and the VCO achieves a tuning range from 6 Hz to 180 kHz.