Patent ID: 6868128

Claim:
A method of calibrating DC offsets in a direct conversion receiver adapted to receive incoming signals wherein the incoming signals are split into In-phase and Quadrature phase signals, and wherein the direct conversion receiver includes an In-phase down converter having a first mixer input and a second mixer input, wherein the first mixer input is adapted to receive the In-phase signal, a Quadrature phase down converter having a first mixer input and a second mixer input, wherein the first mixer input is adapted to receive the Quadrature phase signal, and a local oscillator circuit capable of generating a local oscillation signal having a predetermined original frequency value, and wherein the local oscillation signal is coupled to the second mixer inputs of the In-phase and Quadrature phase down converters, the method comprising the steps of: (a) detecting an inactive time interval during which the direct conversion receiver is not receiving incoming signals requiring processing; (b) shifting the frequency of the local oscillation signal generated by the local oscillator circuit by a selected frequency shift value when an inactive time interval is detected in step (a), wherein the shifting of the frequency of the local oscillation signal effectively isolates the receiver from the incoming signals; (c) measuring a DC offset in the signal generated by the direct conversion receiver; (d) shifting the frequency of the local oscillation signal by the frequency shift value used in step (b), wherein the local oscillation signal is returned to its original frequency value; (e) calibrating the direct conversion receiver for DC offsets by removing the DC offset measured in step (c) from the incoming signals; and (f) returning to step (a).