A frequency mixing circuit and a frequency mixing method. The frequency
mixing circuit includes first and second differential amplifiers, a
subtracter and a mixer. The first differential amplifier amplifies a
first pair of input signals having a first frequency to generate a first
differential signal. The second differential amplifier amplifies a second
pair of input signals having the first frequency orthogonal to the first
pair input signals to generate a second differential signal. The
subtracter subtracts the second differential signal from the first
differential signal. The mixer mixes the subtracted signal with a first
and second pairs of drive signals having a second frequency orthogonal to
each other, in a sub-harmonic double balanced mixing mode, so that the
mixer generates a pair of output signals orthogonal to each other without
secondary harmonics.