A linear CMOS OTA for VHF applications

The design of a linear, fully-balanced, voltage-tunable CMOS operational transconductance amplifier (OTA) with improved gain and very wide bandwidth is described. It uses a cross-coupled, two-differential-pair transconductor 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 any bandwidth limitation. SPICE simulation results show THD<1% at 1.9 V_p-p with dynamic range equal to 63 dB at a power consumption of 2.7 mW from a single 5-V supply. Application to a lowpass filter in the VHF range is presented as an example, assuming implementation in a standard 2 μm CMOS process (MOSIS). The cutoff frequency of the filter is tunable in the range of 8.3-50.0 MHz