| 摘要 |
A mixer is provided having a mixing element, an input signal port for incoming signals at a frequency fIN, a local oscillator signal port for signals from a local oscillator having a fundamental frequency fLO, and an output port from which the resultant frequency may be taken. Means are provided to impose a DC component of bias voltage across the mixing element at one of three levels. The mixer is such that it has a pair of conduction threshold voltages which are substantially symmetrical above and below zero volts, beyond which the mixing element will be conductive at least when a signal from the local oscillator is imposed on it. The signal from the local oscillator has substantially sinusoidal voltage waveform, with a peak-to-peak voltage which is greater than the voltage difference between the pair of conduction threshold voltages. When the first zero DC component bias voltage is imposed across the mixer element, the mixing element is conductive in respective symmetrical positive-going and negative-going senses, and the maximized resultant frequency is |fIN+/-2fLO|. When the second DC component of bias voltage is imposed across the mixing element, it conducts only once per cycle of local oscillator voltage, so that the maximized resultant frequency is |fIN+/-fLO|. When the third DC component of bias voltage is imposed across the mixing element, the value of voltage across the mixing element exceeds the threshold voltage in the same sense as the voltage shift for about 35% to about 55% of the period of the local oscillator voltage cycle making the mixer conductive, but it is also conductive in the opposite sense for at least a portion of the remaining period of the cycle, so that third harmonic mixing occurs, and the maximized resultant frequency is |fIN+/-3fLO|.
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