Modulation or frequency conversion by time sharing

摘要

A switching signal drives a time-share mixer circuit to alternate between two output signals. The first output signal represents the output of a mixer (123) having a given signal input and a local oscillator (127) 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 modulator uses the time-share mixer circuit in combination with an I - Q switching element (199) (Fig. 11, not shown) that alternately couples first and second information signals to the mixer and a bandpass filter (201) that filters the output of the mixer to provide the I - Q modulated signal. The demodulator uses the time-sharing mixer circuit in combination with an output I - Q switching element (203) (Fig. 12, not shown) that alternates the output signal from the mixer between first and second low pass filters (205) and (207) to provide the demodulated I and Q signals. The frequency converter uses the time-share mixer circuit in combination with a switched output phase shifter (209) (Fig. 13, not shown) 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 filtered by a filter and amplified as desired by a bandpass amplifier. A clocked inverter in series with one of the mixer input or output ports provides improved performance by eliminating the need for two precisely phase-shifted local oscillator signals.