Operational amplifier topology and method

Abstract

A technique is disclosed which facilitates the layout of op amp cells, for example, two-stage op amp cells or three-stage op amp cells, to provide larger operational amplifiers. In accordance with one aspect, the op amp cells can be suitably coupled in parallel to provide a larger operational amplifier. This paralleling aspect can be facilitated by connecting the respective negative and positive inputs of a predetermined number of input gm stages together, connecting the outputs of a predetermined number of output gm stages together, and connecting a predetermined number of intermediate internal nodes between the input gm stages and the output gm stages together, without the occurrence of saturation of the internal nodes. In addition, the input and output characteristics of operational amplifier can be suitably improved. Further, the plurality of op amp cells can be selectively configurable to be connected in parallel with other op amp cells through the use of, for example, manual switches or other suitable electrical contacts, jumpers and the like, or programmable switches. Moreover, the op amp cells can be suitably configured in various arrangements, such as a two-stage cell having a first gm stage with a single-ended output, a two-stage cell having a first gm stage with a differential output, or a three-stage op amp cell. As a result, the method of the present invention can provide a substantial advantage in the design of integrated circuits in which the development costs are high, and multiple custom mask sets are too expensive to be practical.

Dependencies are inferred from the claim text.