RECURSIVE FILTER CIRCUIT

PROBLEM TO BE SOLVED: To provide a recursive filter circuit of which the size is small by reducing the number of emitter follower circuits in the recursive filter circuit.SOLUTION: The recursive filter circuit includes: a node B for adding a current Iin flowing in a bipolar transistor (Tr) 101 to a feedback current Ifb to generate a current I; a variable gain amplification unit that sets the current I to be a tail current, and includes a differential pair 100 including a bipolar Tr106 and a bipolar Tr103 into which a control signal for changing a gain is inputted and a resistive element 105 for converting a current flowing in the bipolar Tr106 to a voltage; an output unit 115 including a bipolar Tr113 for amplifying the converted voltage to generate an output signal; and a phase-shifting unit including a high-pass unit including a variable capacitance element 104, a circuit 114 for buffering a signal outputted from the high-pass unit, and a low-pass unit for performing frequency band restriction to the buffered signal via a variable capacitance element 109.