A BiCMOS low distortion tunable OTA for continuous-time filters

The use of electronically programmable, bipolar current mirrors in conjunction with a BiCMOS linearized differential input stage produces a linearized transconductance amplifier with an extended high-frequency transconductance adjustment range. Both linearity and transconductance excess phase are largely independent of the transconductance gain over the range of adjustment. HSPICE results show that, for a modest BiCMOS 2- mu m technology (MOSIS) with a +or-2.5-V power supply, a decade of adjustment is obtained for a 2-V p-p input signal with less than 1% distortion, and from a simple phase compensation scheme the excess phase can be kept below 1 degrees for up to 25 MHz. The tuning range and linear operation of a low-frequency version of the OTA are experimentally demonstrated using transistor array ICs.>