Modulation and frequency conversion by time sharing
 A time-share mixer circuit and a frequency converter, an I-Q modulator, and an I-Q demodulator. A switching signal drives the time-share mixer circuit to alternate between two output signals. The first output signal represents the output of a mixer having a given signal input and a local oscillator signal with a first phase as its local oscillator input. The second output signal represents the output of the mixer having the same input signal and the local oscillator signal with a second phase that differs from the first phase by 90 degrees as its local oscillator input signal. The frequency converter uses the time-share mixer in combination with a switched output phase shifter that switches in sync with the phase of the local oscillator signal to generate a phase shifted output signal in which the time average of an undesired image signal is substantially reduced compared to time average of the desired signal. The phase shifted output signal is then amplified by a bandpass amplifier. A clocked inverter in series with one of the mixer ports provides improved performance by eliminating the need for two precisely phase-shifted local oscillator signals. 
Hewlett-Packard Company
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Scott D. Richard C. William J. Andrew Z. Thomas
Willingham Walker McFarland Grzegorek Hornak