This thesis reports an investigation into integrated interface circuits for switched capacitor sensors for application in industrial process control instrumentation networks. Three circuits are presented: an absolute capacitance to voltage converter; a capacitance ratio to frequency ratio converter; and a capacitance ratio to voltage ratio converter. Of the circuits, the first two are subject to most thorough investigation with the capacitance ratio to frequency ratio converter being of particular interest. This circuit is based upon a switched capacitor, frequency controlled, negative feedback loop which permits implementation with modest quality analogue components, such as are provided with a standardcell ASIC CMOS process. Initial investigations, accomplished with discrete component implementations of the interface circuits, reveal a significant departure in behaviour from that predicted by firstorder analysis. Switch induced chargefeedthrough is shown to be responsible for the deviation. In addition, parasitic induced jitter and frequency locking are identified as a second source of error. The three interface circuits are implemented as an integrated circuit using the European Silicon Structures (ES2) ASIC CMOS process, with a modification to permit the inclusion of fullcustom designed, chargefeedthrough compensated switches. This implementation exhibits greatly reduced chargefeedthrough, and circuit behaviour is in accordance with a modification to the firstorder analysis that includes the effects of chargefeedthrough. Importantly, no frequency locking and much reduced jitter is observed. Significantly, linear performance is obtained for the capacitance ratio to frequency ratio converter over a 20 to 1 capacitance range, with operation demonstrable down to 5pF sensor capacitance.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660549 |
| Date | January 1991 |
| Creators | Peter, Kenneth W. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15637 |
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