Multi-stage operational amplifier for portable apparatus with low supply voltage, has input, intermediate and output stages with Miller feedback capacitances to intermediate stage input

摘要

The operational amplifier comprises an input transconductor stage (110) with differential inputs (112-,112+) and an output (114). There is an output stage (150) and an intermediate stage (120,130) between the input and output stages. There is a Miller capacitor (162) connected between the input and the output of the intermediate stage. There is a second Miller capacitance (160) between the input of the intermediate stage and the final output. The amplifier circuit also comprises the means for biasing bipolar transistors in the form of constant current sources (124,134,154), each connected in series with transistor between the supply lines, for the amplifier functioning mode in class A. In the second embodiment, at least one intermediate stage comprises two bipolar transistors biased for functioning mode in class AB, and the bipolar transistor of first intermediate stage comprises two elementary bipolar transistors connected in parallel. The feedback resistance (RE) is chosen so to satisfy the conditions: RE10 is less than kT/q, and REImax/(beta) is greater than KT/q, where 10 is the stationary current traversing the transistor (132) of stage (130) with the feedback resistor (136), Imax is the maximum current traversing the transistor (152) of the next stage (150), and (beta) is the minimum gain.