JPS57152720A - Digital filter with agc - Google Patents

Abstract

PURPOSE:To prevent overflow in the course of operations and to reduce the operation error, by connecting multipliers to the input side and the output side of a digital filter and increasing or reducing multipliers alpha1 and alpha2 while keeping the relation of alpha1=1/alpha2. CONSTITUTION:An input signal D1 is subjected to multiplication of D2=D1.alpha1 by a multiplier 2, and a resultant signal D2 is inputted to a digital filter 1. An increment detecting circuit 5 sets a signal B to 1 if the circuit 5 decides that the input signal D2 to the filter 1 is increasing, and a level detecting circuit 6 sets a signal A to 1 if the circuit 6 detects that the value of the input signal D2 is large enough to cause overflow in the course of operations of the filter. When signals A and B are 1 together, a multiplier generating circuit 7 reduces the value of the multiplier alpha1 and increases the value of a multiplier alpha2 in proportion to this reduction. An output signal D3 of the filter 1 is multiplied by the multiplier alpha2 by a multiplier 3 to obtain an output signal D4. If the amplitude level D2 of the input signal is very small, the level detecting circuit 6 sets a signal C to 1 to increase the value of the multiplier alpha1 and reduces the value of the multiplier alpha2.