Output filter for oversampling digital-to-analog converter

Details Output filter for oversampling digital-to-analog converter Output filter for oversampling digital-to-analog converter

1994-08-26

1996-08-06

Mai, Tan V.

Boots, shoes, and leggings

364825, G06J 100, G06G 702

Patent

active

055440819

ABSTRACT:
In an output filter for an oversampling digital to analog (D-A) converter, an n-tap finite impulse response (FIR) filter of a predetermined characteristic includes a predetermined number of D-type flip-flops (DFFs) and resistors connected to individual taps, and a one-bit output of a delta-sigma modulator 2 is inputted. The filter includes a number of DFFs 11.sub.1 to 11.sub.n-1 commensurate with a number n of taps of the FIR filter connected in cascade and resistors R.sub.0 to R.sub.n-1 connected between tap outputs (Q), (/Q) of the DFFs and a common output terminal (A) of the FIR filter and having resistance values which are in proportion to reciprocal absolute values of filter tap coefficients. For the tap outputs of the DFFs 11.sub.1 to 11.sub.n-1, the positive outputs (Q) or the inverting outputs (/Q) are selected in accordance with the positive or negative sign of the tap coefficients. In another form, the tap outputs (Q or /Q) of the DFFs which are not selected for connection to the positive output terminal of the FIR filter are connected in common to a inverting output terminal (/A) of the FIR terminal by way of resistors R.sub.0 ' to R.sub.n-1 ' which have resistance values equal to corresponding resistors R.sub.0 to R.sub.n-1, respectively.

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Su, et al., "A CMOS Oversampling D/A Converter with a Current-Mode Semi-Digital Reconstruction Filter", Feb. 1993, IEEE International Solid-State Circuits Conference, Digest of Technical Papers, pp. 230-231.
Crouse et al, "Tranversal Filter with Analog-Digital Component", IBM Tech Disclosure Bull vol. 11, No. 7 Dec. 1968, pp. 884-885.

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