High-frequency two-input CMOS OTA for continuous-time filter applications
A high-frequency fully differential CMOS operational transconductance amplifier (OTA) is presented for continuous-time filter applications in the megahertz range. The proposed design technique combines a linear cross-coupled quad input stage with an enhanced folded-cascode circuit to increase the output resistance of the amplifier. SPICE simulations show that DC-gain enhancement can be obtained without significant bandwidth limitation. The two-input OTA developed is used in high-frequency tuneable filter design based on IFLF and LC ladder simulation structures. Simulated results of parameters and characteristics of the OTA and filters in a standard 1.2 μm CMOS process (MOSIS) are presented. A tuning circuit is also discussed.