Successive approximation A/D converter correcting for charge injection offset
US5247299A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 2, 1992 |
| Grant date | Sep 21, 1993 |
| Priority date | — |
| Expiry date | Jun 2, 2012 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03M1/46
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
In a successive-approximation analog-to-digital conversion application, charge injection offset at the sample input of the comparator resulting from the changing DAC reference voltage, is converted to a fixed, systematic offset. In the comparator differential input stage, the reference or driven input device is turned off during a sample time, prior to beginning the conversion process, so that substantially all of a predetermined bias current flows in the sample side of the comparator. Given this initial condition, the change in input voltage through conversion is a fixed function of the device geometry, bias current and gain, independent of the sample voltage, and therefore may be calibrated out of the system. The comparator input stage includes a differential pair of MOS transistors. A CMOS transmission gate is coupled between the DAC output and the reference comparator input. A switch transistor is coupled between the reference input, i.e. the gate of M2, and Vdd for biasing off M2 during sample time. Transmission gate and switch transistor are controlled by a binary control signal "sample/convert" to turn M2 off during a sample time, and to couple the DAC output to the referenc…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.