Microprocessor-controlled OTA-C lowpass and bandpass filters

Abstract

A realization scheme is given of a high input impedance active biquadratic filter circuit which simultaneously gives lowpass and bandpass responses using operational transconductance amplifiers and capacitors (OTA-C). The circuit basically uses two programmable integrators (PIs) and an additional OTA. Microprocessor control of the pole frequency (w o ) and pole-Q (Q) of the filter is achieved by employing a Motorola 68000 microprocessor and peripheral devices. Electronic control of the filter parameters is also available through the OTAs bias currents. The circuit has excellent sensitivity performance and is suitable for implementation in CMOS-technology. The circuit is attractive for applications in music synthesis, speech synthesis, automatic control, etc. where electronic/digital control of the filter parameters is required. Experimental results on the discrete version of the circuit are included.