US 4,636,744 A · Front end of an operational amplifier

Abstract

The front end of an operational amplifier having an improved controlled slew rate and high gain current output capabilities. The amplifier includes a slew enhancement or large signal stage connected in parallel to a normal front end or small signal stage. The small signal stage supplies a transconductance output which is approximately linearly related to the input until its slew rate limit. The slew enhancement stage is designed to provide slew current when the small signal stage reaches its slew rate limit, thereby providing an increased output current response to an increasing differential input voltage beyond the slew rate of the small signal stage. Two pair of differential amplifiers are used in both a large and small signal stage as well as an improved output stage comprising of current mirrors.

Claims19

Dependent claims

In an amplifier circuit having an input stage and an output stage, said amplifier circuit comprising:

a small signal amplification means in said input stage for providing an output current in response to a differential input voltage;
a large signal amplification means in said input stage connected electrically in parallel with said small signal amplification means for providing additional slew current, wherein said large signal amplification means includes an input means connected to an active load means connected to a high gain current mirror means for providing control over when the additional slew current will be added to the output of said small signal amplification means such that slew current is provided only when said input differential voltage is at least a predetermined value;
and
summing means coupled between the outputs of said small signal amplification means and said large signal amplification means for providing a combined output current to said output stage for said amplifier circuit.

1 more element

In an amplifier circuit having an input and an output stage, said circuit comprising:

a small signal amplification means in said input stage for providing an output current in response to a differential input voltage, wherein said small signal amplification means includes two differential pairs of transistors each having two inputs and an output;
a large signal amplification means in said input stage connected electrically in parallel with said small signal amplification means, wherein said large signal amplification means includes two differential transistor pairs, each having two inputs connected in parallel to a corresponding like pair of inputs of said small signal amplification means, for providing additional slew current to said output stage when said differential input voltage is at least a predetermined value or when slew rate limiting occurs, and an active load means connected to each of said transistor pair and a high gain current mirror means connected to each of said active load means for providing control over when the additional slew current will be added to the output of the small signal amplification means;
and
summing means coupled between the outputs of said small signal amplification means and said large signal amplification means for providing a combined output current for said amplifier circuit.

1 more element

Dependencies are inferred from the claim text.

Front end of an operational amplifier

Life of this patent

Front end of an operational amplifier

Life of this patent

Abstract

Claims19