Patent ID: 8594593

Claim:
A frequency converter for converting frequencies of a positive-phase input signal and a negative-phase input signal into other frequencies to obtain a positive-phase output signal and a negative-phase output signal, the positive-phase input signal being inputted into a positive-phase input terminal, the negative-phase input signal being inputted into a negative-phase input terminal, the positive-phase output signal being outputted from a positive-phase output terminal and the negative-phase output signal being outputted from a negative-phase output terminal, comprising: a first pair of transistors including a first transistor and a second transistor, the first transistor including a source terminal being connected to the positive-phase input terminal, a drain terminal being connected to the positive-phase output terminal, and a gate terminal being supplied with a positive-phase local signal; and the second transistor including a source terminal being connected to the positive-phase input terminal, a drain terminal being connected to the negative-phase output terminal, and a gate terminal being supplied with a negative-phase local signal; a second pair of transistors including a third transistor and a fourth transistor, the third transistor including a source terminal being connected to the negative-phase input terminal, a drain terminal being connected to the positive-phase output terminal, and a gate terminal being supplied with the negative-phase local signal; and the fourth transistor including a source terminal being connected to the negative-phase input terminal, and a drain terminal being connected to the negative-phase output terminal, and a gate terminal being supplied with the positive-phase local signal; a variable impedance circuit having an impedance value depending on frequencies of the positive-phase local signal and the negative-phase local signal, one terminal being connected to the positive-phase input terminal, and other terminal being connected to the negative-phase input terminal, wherein the variable impedance circuit includes a plurality of resistor units, each resistor unit including a first resistor having one terminal being connected to the positive-phase input terminal and other terminal, a second resistor having one terminal being connected to the negative-phase input terminal and other terminal, and a switch connected between the other terminals of the first resistor and the second resistor, and capable to turn ON and OFF, and the variable impedance circuit is capable to vary the impedance value by turning the switches of the resistor units ON and OFF, wherein the variable impedance circuit turns the switches ON and OFF to satisfy a resistance value R=(1/Z−4fLO*Cgd) −1 , where fLO is a frequency of the positive-phase local signal and the negative-phase local signal, Z is an input impedance value at between the positive-phase input terminal and the negative-phase input terminal, Cgd is a capacity between the gate terminal and the drain terminal of each of the first to fourth transistors.