A rail-to-rail, constant gain, buffered op-amp for real time video applications

Abstract

Inspired by Hogervorst et al's current switch idea, a buffered output stage operational amplifier was designed, which has high frequency, high dc gain, and rail-to-rail constant transconductance (G/sub m/). This operational amplifier is the output stage of an analog/digital system which implements a Gabor convolution for real-time dynamic image processing and it is designed to interface the external analog-to-digital converter (ADC) with a very heavy load. The op amp was fabricated by the MOSIS service in a 2-/spl mu/m, n-well CMOS, double polysilicon, double metal technology. The fabricated circuit operates from a single 5 V power supply and dissipates 10 mW. The open loop-gain of the fabricated circuit, A/sub vol/, was measured as 67.2 dB for a 163 /spl Omega//spl par/33 pF load. Other dc and ac characteristics were measured for a 50 /spl Omega//spl par/33 pF load. The unify gain-bandwidth (GBW) was measured to be 11.4 MHz, the rising slew rate (SR+) 20.4 V//spl mu/s, the falling slew rate (SR-) 18.8 V//spl mu/s, and the offset voltage (V/sub off/) 1 mV. The output swings with an amplitude of 3.24 V between 0.88 V and 4.12 V, which matches the input signal specifications of the ADC. In addition to rail-to-rail output voltage swing, the opamp has a constant G/sub m/ over the whole common mode (CM) voltage range.