Output filter for delta sigma modulator and digital signal processor provided with the same
AssigneeRohm Co., Ltd.
InventorMasakazu Fukuda
Life of this patent
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Abstract
The invention intends to reduce noises by resistors in an output filter for a delta sigma modulator. The output filter uses an FIR filter with constant current sources as the current source, extracts output data of the delta sigma modulator from each taps of a shift register, controls MOS transistors by the extracted delayed signals, attains currents weighted according to the FIR filter coefficients corresponding to the number of the taps from the constant current sources, adds the currents attained, and performs the current-to-voltage conversion of the currents thus attained by feedback resistors of a full differential operational amplifier.
Claims6
An output filter for a delta sigma modulator, comprising:
- a first and a second constant current source having first and second outputs, respectively;
- a FIR filter having a plurality n of delay element arranged in cascade, where n is a whole number greater than two, each element being operative to output data of the delta sigma modulator by controlling currents via n switches from the first and second constant current sources on the basis of each of the output data to thereby generate a plurality of weighted currents that are weighted according to a filter characteristic, the weighted currents being added separately for inverted and non-inverted signals and outputted separately at an output side of the FIR filter;
- and
- a current-to-voltage conversion unit, said unit having an input side coupled to the output side of the FIR filter and comprising a full differential operational amplifier and feed back resistors, said amplifier having a pair of inputs, each input coupled to a respective one of each separate output of said FIR filter and having an output side.
Dependencies are inferred from the claim text.