Amplifier circuit with distortion cancellation function

Claim 1

An amplifier circuit with distortion cancellation function comprising: (a) input terminal means for receiving an input signal to be amplified; (b) main amplifier means for amplifying said input signal, said main amplifier means having an input terminal for being supplied with a signal proportional in signal level to said input signal, a reference voltage input terminal for being supplied with a reference voltage, and an output terminal for outputting an output signal thereof, a voltage potential of the input terminal of said main amplifier means at the time when a signal level of said input signal is zero being determined by said reference voltage; (c) impedance circuit means for being supplied with said output signal of said main amplifier means; (d) differential amplifier means for supplying an output signal thereof to said reference voltage input terminal as said reference voltage, one of input terminals of said differential amplifier means being supplied with the output signal of said main amplifier means through said impedance circuit means, the other of the input terminals of said differential amplifier means being supplied with said input signal to be amplified, an output terminal of said differential amplifier means being coupled to the reference voltage input terminal of said main amplifier means; and (e) output terminal means for deriving the output signal of said main amplifier means therefrom; wherein said main amplifier means is a current input type amplifier in which the input terminal is controlled by a current of said input signal; wherein said main amplifier means has a transfer function of one (1) between said reference voltage input terminal and said output terminal; wherein said main amplifier means comprises a first resistor, a second resistor having a resistance value R2, a third resistor having a resistance value R3, and an amplifier having an open-loop gain A and having inverting input, non-inverting input and output terminals, said non-inverting input terminal being connected to the input terminal of said main amplifier means, said first resistor being connected between said non-inverting input terminal and said reference voltage input terminal, said second resistor being connected between said inverting input terminal and said reference voltage input terminal, said third resistor being connected between the inverting and output terminals of said amplifier; wherein said differential amplifier means has a voltage gain B; and wherein said impedance circuit means comprises a fourth resistor having a resistance value R4 and a fifth resistor having a resistance value R5, said fourth and fifth resistors being serially connected in this order between the output terminal of said main amplifier means and ground, a junction point of said fourth and fifth resistors being connected to said one of the input terminals of said differential amplifier means, and wherein R2/( R2+R3)=R5/(R4+R5), A>>0, and B>>0.