A CMOS transconductance-C integrator structure with wide-band programmability and phase lead/lag compensations

The design of a digitally programmable transconductance amplifier (TA) suitable for high-frequency signal processing is presented. The circuit uses switchable differential transconductance elements and a differential folded cascode output stage. An integrator structure based upon this fully differential TA is proposed to serve as the basic building block of programmable continuous-time filters. The structure employs a compensation scheme which provides phase error correction at unity gain frequencies throughout its adjustment range. Limitations on practical filter applications of this structure have been addressed. A simulation shows that the unity gain frequency of this integrator structure can be programmed between 200 kHz and 20-MHz with 3-pF load. The transconductance gain of a prototype transconductance amplifier fabricated in a 2-μm CMOS process was experimentally adjusted and measured from 3 μA/V to 1.3 mA/V