Frequency conversion circuit, modulation circuit, polar modulation transmitting circuit, quadrature modulation transmitting circuit, communication instrument, and frequency conversion method

Abstract

A frequency conversion circuit is provided capable of suppressing noise converted from about a frequency twice as large as a local signal to a reception band frequency, which performs modulation by mixing an input signal with a local signal. The frequency conversion circuit includes a first transistor whose base is electrically connected with one of a first input terminal pair inputted with the input signal; a second transistor whose base is electrically connected with the other of the first input terminal pair; third and fourth transistors whose emitters are electrically connected respectively with a collector of the first transistor; fifth and sixth transistors whose emitters are electrically connected respectively with a collector of the second transistor; and a differential noise suppression circuit provided between the collector of the first transistor and the collector of the second transistor. The differential noise suppression circuit includes at least one capacitor, which suppresses a differential noise component of a frequency twice as large as a local signal frequency without repeating charging or discharging of the capacitor with at least the local signal frequency.