Cancellation techniques for LO leakage and Dc offset in direct conversion systems

Abstract

This paper presents LO leakage and dc offset cancelling techniques for direct conversion systems. Dc offset at the mixer output, partially due to LO leakage, degrades system sensitivity by inducing Flicker noise, while LO leakage on the antenna side may cause additional interference. To reduce these problems, LO leakage and dc offset cancelling techniques were studied for both transceiver and receiver configurations. Using a mixer LO leakage canceller for the receiver configuration, zero dc offset and 17dB of LO leakage reduction were achieved. Flicker noise was also reduced by 19.3 dB as a result of the minimized dc offset. In a transceiver configuration, simultaneous cancellation of LO leakage and transmit signal leakage resulted in a 21.7dB reduction in Flicker noise. This transceiver compensation technique can also be used to cancel clutter reflections.