Abstract: A tuning circuit which has a wide tuning bandwidth. The tuning bandwidth of the tuning frequency can be easily changed. The tuning circuit 1 is composed of two cascade-connected tuning amplifier sections 2 and 3. Each of the sections 2 and 3 is provided with cascade-connected phase-shifting circuits 10C and 30C, a voltage dividing circuit 60, and an adding circuit composed of a feedback resistor 70 and an input resistor 74. Prescribed tuning operation is performed by shifting the phase of a prescribed frequency by 360.degree. by means of the phase shifting circuits 10C and 30C and setting the open loop gain of a feedback loop at less than 1 when the output of the voltage dividing circuit 60 is feedback. The resistance ratio between the feedback resistor 70 and input resistor 74 of each tuning amplifier section is adjusted in order that the maximum damping of each tuning amplifier section becomes smaller and the tuning bandwidth of each amplifier section becomes wider.

Abstract: A tuning circuit which has a wide tuning bandwidth. The tuning bandwidth or the tuning frequency can be easily changed. The tuning circuit 1 is imposed of two cascade-connected tuning amplifier sections 2 and 3. Each of the sections 2 and 3 is provided with cascade-connected phase-shifting circuits 10C and 30C, a non-inverting circuit 50, a voltage dividing circuit 160, and an adding circuit composed of a feedback resistor 70 and an input resistor 74. Prescribed tuning operation is performed by shifting the prescribed frequency 360.degree. by means of the phase shifting circuits 10C and 30C and setting the open loop gain of a feedback loop at less than 1 when the output of the voltage dividing circuit 160 is feedback. The resistance ratio between the feedback resistor 70 and the input resistor 74 of each section 2, 3 is adjusted so that the maximum damping of each section 2, 3 may become smaller and the tuning bandwidth of each section 2, 3 becomes wider.

Abstract: A tuning amplifier 1 is provided with two cascade connected phase shifting circuits 10C and 30C and an adding circuit composed of a feedback resistor 70 and input resistor 74. The circuit 10C is constituted of an operational amplifier 12, a resistor 18 one end of which is connected to the inverting input terminal of the amplifier 18, a resistor 20 connected between the inverting input terminal and the output terminal of the amplifier 12, a series circuit which comprises a capacitor 14 and a variable resistor 16 and one end of which is connected to the other end of the resistor 18. The fluctuation of the output amplitude of the circuit 10C is suppressed when the tuning frequency of the circuit 10C is changed because the resistance of the resistors 18 and 20 are equal to each other.

Abstract: A tuned amplifier that can be produced easily in an integrated circuit and by which the tuning frequency and the maximum damping are arbitrarily adjusted without mutual interference.