Image reject mixer, circuit, and method for image rejection

DETAILED DESCRIPTION According to a first aspect of the present invention there is provided an integrated image reject mixer circuit responsive to an information-bearing signal and arranged to be coupled to a local oscillator that provides phase-referenced signals thereto and wherein the information-bearing signal has in-phase and quadrature components, the integrated image reject mixer circuit comprising: circuit arrangements of first, second, third and fourth mixer paths each containing: a signal input for receiving the information-bearing signal; a mirrored pair of mixer transistors for receiving selected phase-referenced signals, each mirrored pair of mixer transistors further configured to receive a dedicated phase aligned information-bearing signal for frequency down conversion to a respective intermediate frequency component through mixing with one of the selected phase-referenced signals; and a polyphase filter integrally formed directly between the signal inputs and the mirrored pairs of mixer transistors of each of the first, second, third and fourth mixer paths such that the phase aligned information-bearing signals in each of the respective first, second, third and fourth mixer paths are generated within each mixer path and have a substantially quadrature phase shift therebetween.
Preferably, the phase-referenced signal applied to each mirrored pair of mixer transistors has a frequency such that mixing with the information-bearing signal forms an intermediate frequency signal having a frequency offset relative to DC that is in an approximate range of between a half channel spacing and a single channel spacing.
Beneficially, integration of the polyphase filter can be achieved with an overall reduction in the number of components in view (particularly) of the elimination of the requirement to provide discrete buffering components and the advantage that the polyphase filter and the image reject mixer can be current driven (without imposing an increased drain on any available power source, such as a battery)