Digital filter

A digital filter, comprising:

• a multiplexer that is fed pieces of data on M channels (M being an integer equal to or larger than two) at a sampling frequency fs, and generates time-division-multiplexed data formed of the pieces of data on the M channels that are time-division multiplexed, the pieces of data on the respective channels being updated at a rate equal to the sampling frequency fs;
• a plurality of integration calculation circuits that are cascade-connected to an output of the multiplexer, operate in accordance with a first clock having a frequency fs×M, and integrate the time-division-multiplexed data for every M samples;
• a frequency conversion circuit that operates in accordance with a second clock having a frequency fD×M for performing sampling on each of the channels at a frequency equal to a sampling frequency fD=fs/N (N being an integer equal to or larger than two), decimates data at the sampling frequency fs input from an integration calculation circuit in a last stage among the integration calculation circuits at the sampling frequency fD, and delays data obtained as a result of decimation by (M−1) samples;
• and
• a plurality of difference calculation circuits that operate in accordance with the second clock having the frequency fD×M for performing sampling on each of the channels at the frequency equal to the sampling frequency fD, are cascade-connected to an output of the frequency conversion circuit, and each subtract, from data input thereto, data M samples before the input data.