Stabilized transient response of a cascode CMOS amplifier
US5202645A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 12, 1991 |
| Grant date | Apr 13, 1993 |
| Priority date | — |
| Expiry date | Dec 12, 2011 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03F3/45188
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
Operational amplifiers are often used in unity gain configurations where the output is fed back to the input. In the noninverting buffer configuration the output is directly connected to the inverting input and the circuit becomes a voltage follower. In many cases, the input stage includes cascode coupled transistors which isolate the current mirror load from the differentially operated input transistors. Such cascode transistors act to increase gain to reduce noise and to increase the power supply rejection ratio. When cascode coupled transistors are employed the frequency compensation capacitor can be isolated from loading effects on the input stage, thus, further enhancing the value of a cascoded input stage. However, when such an operational amplifier is operated as a unity gain device its transient response can suffer. Negative output transitions can result in circuit ringing following the negative output transient steps. The invention consists of adding constant current transistors in parallel with the first stage current mirror load elements. It has been shown that such constant current transistors remove the ringing problem without degrading any of the desired circuit param…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.