A linear fully balanced CMOS OTA for VHF filtering applications

A linear, fully balanced, voltage-tunable CMOS operational transconductance amplifier (OTA) with large de gain and wide bandwidth is described. The approach uses a two-differential-pair transconductor with a cross-coupled input stage together with a negative resistance load for compensating the parasitic output resistance of the OTA. Since no additional internal nodes are generated, dc gain enhancement is obtained without bandwidth limitation. SPICE simulations show that total harmonic distortion at 1.42 Vp-p is less than 1% with dynamic range equal to 66 dB at a power consumption of 2.7 mW from a single 5-V supply. As an example, the OTA is used to design a third-order elliptic lowpass filter in the very-high-frequency range, simulated in a standard 2 mu m CMOS process (MOSIS). The cutoff frequency of the filter is tunable in the range of 12-50 MHz.