IMPROVED METHOD AND APPARATUS FOR UP- AND DOWN- CONVERSION OF RADIO FREQUENCY (RF) SIGNALS

摘要

This patent describes a method and system which overcomes the LO-leakage problem during modulation and demodulation, common to direct conversion and similar RF transmitters and receivers. This problem is solved using a virtual local oscillator (VLO) signal which emulates mixing with a local oscillators (LO) signal. The VLO signal is constructed using complementary mixing signals that suppress mixing power in the bandwidth of the input signal, and within the bandwidth of the output frequency. Specifically, mixing is done in two or more stages, using time-varying mixing signals phi 1 and phi 2 which satisfy the following criteria: phi 1 * phi 2 having significant power at the frequency of the LO being emulated, one of phi 1 and phi 2 having minimal p ower around the frequency of the output signal y(t), and the other of phi 1 and phi 2 having minimal power around the centre frequency, fRF, of the input signal x(t).