Digitally tunable continuous-time filters for VLSI
Digitally tunable continuous-time filters for VLSI
The development of a VLSI-compatible digitally tunable continuous-time filtering technique is described. Simple passive and active structures are combined in a standard op-amp RC configuration to realise very high signal performance. Each time-constant determining capacitor in the filter is replaced with a programmable array of highly linear passive capacitors. The array value is automatically fixed to correct process and temperature induced errors in the filters' RC time-constants. Linear polysilicon resistors and high performance single-ended or fully-balanced op-amps complete the design. A detailed description of the design of one such fully-balanced op-amp is given. The most suitable array and filter topologies are discussed with respect to performance, especially linearity. The code needed to fix the array values is derived using on-chipcalibration circuitry. A reference clock with fixed period is the only external requirement. A new calibration scheme is presented and its measured performance is discussed. The fabricated filters designed using the optimised techniques exhibit a mean dynamic range of + 95dB and a mean signal THD of around -90dB for a differential output signal of 2Vrms and a fundamental input signal frequency of up to 20 kHz. Such performance is compatible with the dynamic range of 16-bit sampled data processors. The area per pole of the most complex of these filters is comparable to that of other, lower performance, integrated continuous-time filters. A novel digitally tunable OTA-C filter is developed and shown (in simulation only) to have signal performance similar to that of the op-amp RC filters. A digitally tunable op-amp RC filter technique is extended and applied to the design of a fourth-order 1 bit Σ-Δ analogue-to-digital converter. The converter was fabricated and was fully functional with unconditional stability.
University of Southampton
1992
Durham, Anna Mary
(1992)
Digitally tunable continuous-time filters for VLSI.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The development of a VLSI-compatible digitally tunable continuous-time filtering technique is described. Simple passive and active structures are combined in a standard op-amp RC configuration to realise very high signal performance. Each time-constant determining capacitor in the filter is replaced with a programmable array of highly linear passive capacitors. The array value is automatically fixed to correct process and temperature induced errors in the filters' RC time-constants. Linear polysilicon resistors and high performance single-ended or fully-balanced op-amps complete the design. A detailed description of the design of one such fully-balanced op-amp is given. The most suitable array and filter topologies are discussed with respect to performance, especially linearity. The code needed to fix the array values is derived using on-chipcalibration circuitry. A reference clock with fixed period is the only external requirement. A new calibration scheme is presented and its measured performance is discussed. The fabricated filters designed using the optimised techniques exhibit a mean dynamic range of + 95dB and a mean signal THD of around -90dB for a differential output signal of 2Vrms and a fundamental input signal frequency of up to 20 kHz. Such performance is compatible with the dynamic range of 16-bit sampled data processors. The area per pole of the most complex of these filters is comparable to that of other, lower performance, integrated continuous-time filters. A novel digitally tunable OTA-C filter is developed and shown (in simulation only) to have signal performance similar to that of the op-amp RC filters. A digitally tunable op-amp RC filter technique is extended and applied to the design of a fourth-order 1 bit Σ-Δ analogue-to-digital converter. The converter was fabricated and was fully functional with unconditional stability.
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Published date: 1992
Identifiers
Local EPrints ID: 461010
URI: http://eprints.soton.ac.uk/id/eprint/461010
PURE UUID: 12b8204c-dabb-4620-ac56-ed1215aab217
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Date deposited: 04 Jul 2022 18:33
Last modified: 04 Jul 2022 18:33
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Contributors
Author:
Anna Mary Durham
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