High performance CMOS transconductor for mixed-signal analog-digital applications

This paper describes a CMOS building block dedicated to high performance mi xed analog-digital circuits and systems. The circuit consists of six MOS tr ansistors realizing a new wideband and tunable transconductance. The theory of operation of this device is presented and the effects of transistor non idealities on the global performances are investigated. Use of the proposed circuit to realize tunable functions (Gm-C filter and current opamp) is il lustrated. HSPICE simulations show a wide tuning range of the transconducta nce value from 40 mu S to 950 mu S (500 mu S) for +/- 2.5 V (+/- 1.5 V) sup ply voltages. The transconductance value remains constant up to frequencies beyond 500 MHz. The bandpass filter built with few transconductance blocks and capacitances was simulated with +/- 2.5 V supply voltage, the center f requency is tunable in the range of 30 MHz to 110 MHz. However, the opamp, which is designed with a transresistance-transconductance architecture, was simulated with +/-1.5 V supply voltage. The gain of the opamp can be tuned between 70 dB and 96 dB and high gain-bandwidth product of 145 MHz has bee n achieved at power consumption of less than 0.5 mW. Experimental results o n a fabricated transconductor chip are provided.