CMOS operational transconductance amplifiers with extended transconductance adjustment ranges

Techniques are developed for realizing CMOS transconductance amplifiers with increased transconductance adjustment ranges. In transconductor-based electronic systems, the transconductance adjustment is useful in overcoming integrated circuit process variations and in implementing systems with programmable specifications. Linearity of the transfer characteristic is also highly desirable; however the adjustment of previously-reported transconductors via adjustment of a tail current in a differential-pair-based input stage typically involves severe linearity degradation. The techniques presented in this work are based on the use of programmable current mirrors as a means of transconductance adjustment; furthermore, current mirrors are presented which actually perform the desired linearization of the currents generated by a simple differential pair input stage. This leads to fairly simply transconductor circuits which largely avoid the adjustment/linearity tradeoffs inherent in many previous designs. Experimental results verify the extended adjustment/linearization schemes. A detailed analysis of mismatch effects is included which suggests methods by which these undesirable effects may be reduced.