DIGITAL FILTER

PURPOSE:To prevent noise from being introduced in a filter output by initializing an input data in a delay circuit and stored in a storage means such as a RAM to a prescribed value just after the filter operation, then starting the filter operation actually. CONSTITUTION:An address signal AD1, a write enable signal WE1 and an initializing signal IS are supplied to an initializing address generating circuit 5. Then an address signal AD3 incrementing sequentially from '0' is supplied to a RAM 8 in a timing when a digital filter starts its operation and initialization that a write enable signal WE2 is used to write a data '0' to addresses '0'-'r' is implemented. When a data '0' is written to all (r+1) sets of addresses and the initializing is finished, the filter operation is started. Thus, since no uncertain data is stored in the RAM 8 at the time of starting filter operation, the filter output does not arrive in the vicinity of a maximum value just after the filter operation is started.