Multiple output allpass switched capacitor filters

Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters

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328151, 328167, 330109, H03H 1900, H03H 1112, H03H 1134

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active

047163887

ABSTRACT:
This invention comprises two separate topologies for implementing a second order allpass function filter which is vital for equalization of the phase of other arbitrary response magnitude shaping filters. While the allpass response itself does not affect the frequency spectrum of the signal, these topologies have available outputs that have either bandpass or bandstop characteristics. Thus, two types of useful frequency characteristics formed by the filters that have exactly the same resonant frequency and Q (or Quality factor). Using the well known general two amplifier topology to implement a monolithic switched allpass filter with a high Q leads to very high capacitance ratios and hence excessive silicon area in manufacture. Both the topologies described here reduce the required silicon area by either reducing the required capacitance ratios or making the sensitivity to the smallest capacitor extremely small allowing it to violate otherwise necessary area-to-perimeter matching of the capacitor geometries. Reducing the overall silicon area reduces the overall cost of producing the filters and allows more functionality to be integrated on a single silicon chip.

REFERENCES:
patent: 4210872 (1980-07-01), Gregorian
patent: 4315227 (1982-02-01), Fleischer et al.
patent: 4531106 (1985-07-01), Ganesan
White et al., "A Monolithic Dual-Tone Multifrequency Receiver", Int. Solid State Conference, Digest of Technical Papers, Feb. 1979; pp. 36-37.
McCreary et al.-"All-MOS Charge Redistribution Analog to Digital Conversion Techniques-Part 1", IEEE Journal of Solid-State Circuits, vol. SC-10, Dec. 1975, pp. 371-379.
Martin et al.-"Exact Design of Switched-Capacitor Bandpass Filters Using Coupled-Biquad Structures", IEEE Trans. on Circuits and Systems, Val. SA-27, No. 6, Jun. 1980; pp. 469-475.
Gregorian et al.-"Switched-Capacitor Filter Design Using Cascaded Sections", IEEE Trans. on Circuits and Systems, vol. CAS-27, No. 6, Jun. 1980, pp. 515-522.

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