DIGITAL-ANALOG CONVERTING CIRCUIT

PURPOSE:To perform D/A conversion with a simple constitution by outputting data of individual operation terms of a digital filter in time division and integrating successively an analog signal obtained by D/A conversion of these data to obtain an analog signal corresponding to the sum of individual operation terms. CONSTITUTION:A digital filter part 3a calculates terms of a transfer function expressed with (AS +BS+C) individually and outputs data of the calculation results to a D/A converting part 3e in time division and supplies a control signal (H/L) having a pulse width DELTAT to a switch 3b in accordance with the output of each term. The analog signal outputted from the D/A converter 3e is supplied to an integrating circuit 3d consisting of a resistance R, a capacitor C, and an operational amplifier 3c through the switch 3b during the period DELTAT. The integrating circuit 3d integrates the input signal and holds the integrated value in the period when the switch 3b is turned off. Consequently, analog signals corresponding to individual terms of the transfer function which are inputted successively are integrated to obtain an analog signal corresponding to the transfer function.