CMOS high gain amplifier utilizing positive feedback

Claim 1

A CMOS operational amplifier of the type which includes an inverting input, a non-inverting input and an output, comprising: an input stage including a first input N-channel field effect transistor having a gate coupled to said non-inverting input, and having source and drain electrodes; a second N-channel field effect transistor having a gate coupled to said inverting input and having source and drain terminals; a third N-channel field effect transistor having a gate coupled to a source of a reference voltage, a drain coupled to the sources of said first and second transistors, and a source coupled to a first source of supply voltage; a first P-channel field effect transistor having a source coupled to a second source of supply voltage and having a gate coupled to its drain and to the drain of said first N-channel field effect transistor; and a second P-channel field effect transistor, having a source coupled to said second source of supply voltage, a gate coupled to the gate of said first P-channel field effect transistor and a drain coupled to the drain of said second N-channel field effect transistor, said first and second P-channel field effect transistors being coupled in current mirror relationship with said first and second N-channel field effect transistors and said third N-channel field effect transistor acting as a current sink; a bias stage coupled between said output and said input stage for internally biasing said output in its active region; a first gain stage coupled to said bias stage and to said input stage; a second gain stage coupled to said input stage, said first gain stage and to said output; and a first capacitor coupled between said output and the input of said first gain stage for producing positive feedback and improving the frequency performance of said amplifer.