Method and apparatus for calibrating a local oscillator in a direct conversion receiver

This invention relates to receiver circuits and more specifically to tuning methods for PLL circuits. A receiver includes a main loop () having a main VCO () and a secondary loop () having a secondary VCO (). The receiver momentarily phase locks an incoming RF signal (), and then samples and stores a correction voltage () being applied to the main VCO (). The main loop () is then put into a non-phase locked mode of operation and the stored correction voltage is applied through a receive automatic tuning circuit () to the main VCO () for the duration of the incoming RF signal (). This effectively calibrates the LO frequency () of the receiver to the incoming RF signal frequency ().