CMOS Transconductor Research Articles

Saturation-mode CMOS transconductor with enhanced tunability and low distortion

A new transconductor based on MOS transistors operating in saturation is presented. Linearisation is based on an offset biased pair in a cross-coupled configuration. Simulation results show that the proposed convertor combines excellent tuning characteristics with a large signal handling capability.

New folded cascode transconductor for bandpass ladder filters

The problems of designing CMOS transconductors for high frequency bandpass ladder filters are discussed, and an original circuit for overcoming these problems is presented. This circuit features a new grounded-quad input stage, a very high output impedance and the facility of low impedance inputs to avoid the requirement for transconductance ratios in scaled filters. The application of the new transconductor is illustrated by the design of a high frequency sixth-order Chebyshev bandpass filter. The performance of the transconductor and the filter are demonstrated by analysis and simulation results.

Comparison of four CMOS transconductors for fully integrated analogue filter applications

An analysis of four transconductors based on CMOS transistors operating in saturation is presented and computer simulated performances are compared. It is shown that an antiphase source-coupled pair offers superior tuning characteristics and exhibits low distortion at large input drives.

Design of linear tunable CMOS differential transconductor cells

A general method for the construction of highly-linear CMOS differential transconductor cells (DTCs) is presented. Basic assumptions which allow several tunable CMOS trans-conductance cells to be formed are discussed. The method is based on the simplified square-law relationship of the MOSFET transistor. Extensive SPICE simulation results with MOSFET parameters as realistic as possible confirm the theory.

Design of a very linear CMOS transconductance input stage for continuous-time filters

A CMOS differential input stage for transconductance amplifiers that combines a low noise excess factor, low input capacitance, and high common-mode rejection ratio with a very good linearity is described. The measured distortion is only 0.2% for a 1-V RMS input signal and only 1% for a 2-V RMS input signal on a test circuit implemented in a standard 3- mu m CMOS process, using +or-5-V supplies, resulting in over 85 dB of dynamic range. Applications include high-performance continuous-time filters and linear amplifiers. >

Simple high-frequency CMOS transconductor

A new transconductor, using only two transistors, is presented. It is based on standard inverter configurations and does not need matching of nMOS and pMOS transistors or of the power supply voltages. Reduction in nonlinearity is achieved by maintaining a zero offset condition. The circuit is not affected by variations in body effect as sources and substrates are connected to fixed voltages. Although the inverter has a low signal level handling capability (≃300mV for a total harmonic distortion of 1%), this can be improved by the use of two inverters. This leads to a larger dynamic range and has no noticeable effect on bandwidth.A wideband integrator is developed, based on the new transconductor, with independent adjustment of quality factor and unity-gain frequency.

CMOS variable transconductance circuit with constant bandwidth

The authors propose a new linear CMOS transconductor circuit. It has a transconductance linearly variable by a gate voltage and a rather high bandwidth. Moreover, this bandwidth remains constant when the transconductance is varied. The circuit exploits the square-law characteristic of MOS transistors biased in saturation.< >

High-frequency voltage-controlled continuous-time lowpass filter using linearised CMOS integrators

The design and implementation of a continuous-time lowpass filter with voltage-controlled cutoff frequency and passband ripple is presented. The circuit uses a linearised CMOS transconductor as a basic integrating building block. A voltage-controlled phase-adjusting scheme is employed in the integrator to compensate for excess phase in the transconductance at high frequencies. The fabricated filter is capable of realising cutoff frequencies as high as 2 MHz and handles single-ended input signals up to 4 V p-p with less than 1% distortion.