Output filter for over-sampling digital-to-analog converter.

摘要

In an output filter for an oversampling D-A converter of the present invention, an n-tap FIR filter of a predetermined characteristic is constituted from a predetermined number of 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 111 to 11n-1 equal to a number n of taps of the FIR filter in cascade connection and resistors R0 to Rn-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 numbers to absolute values of filter tap coefficients. For the tap outputs of the DFFs 111 to 11n-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, those 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 R0' to Rn-1' having resistance values equal to corresponding resistors R0 to Rn-1, respectively.