Analogue-to-digital converters and digital modulators

Details Analogue-to-digital converters and digital modulators Analogue-to-digital converters and digital modulators

1994-09-09

1996-12-17

Hoff, Marc S.

Coded data generation or conversion

Analog to or from digital conversion

Differential encoder and/or decoder

341166, H03M 302

Patent

active

055858015

ABSTRACT:
In a conventional sigma-delta converter/modulator, quantisation noise of the quantiser which produces the digital output is suppressed because of a feedback loop which feeds an error signal via a filter to the quantiser, the error signal being the difference between the digital output and the input. Improved noise suppression is achieved by more filter stages, but such converter/modulators require special measures to reset them in the event of an overload i.e. a high input signal. A modified output is taken from the filter which is such that a second filter appears, when the main loop is not overloaded, to be in a loop with a simple delay, i.e. a sigma-delta circuit. The main loop has the inherent recovery properties of a second order modulator/converter and cannot be swamped by the signal from the second loop because of a limiter and, when the main loop has recovered, so does the second loop containing second filter. However, the quantisation noise is now suppressed by the combined filters. In an analogue equivalent, the limiter receives a signal representative of each of those filter orders to permit an equivalent impulse response to be provided.

REFERENCES:
patent: 5055846 (1991-10-01), Welland
patent: 5124703 (1992-06-01), Kaneaki et al.
patent: 5208594 (1993-05-01), Yamazaki
patent: 5243345 (1993-09-01), Naus et al.
patent: 5392039 (1995-02-01), Thurston
IEEE Journal of Solid-State Circuits, vol. 28, No. 3, Mar. 1993, "A Fourth-Order Bandpass Sigma-Delta Modulator", Jantzi et al., pp. 282-291.

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