Direct current offset cancellation for mobile station modems using direct conversion

A method for cancelling DC offset in an RF receiver having a direct converter for direct down conversion of a received RF signal to a baseband signal, said method comprising the steps of:

• (1) applying a high gain to expand the bandwidth of a high pass filter when a gain change occurs in said RF receiver;
• (2) rapidly acquiring the DC offset within said baseband signal prior to the timing out of a timer;
• (3) applying a low gain to narrow the bandwidth of said high pass filter when the timer has timed-out;
• and
• (4) tracking the DC offset to fine tune the acquired DC offset, wherein the DC offset is removed from the baseband signal.

A DC offset cancellation block, comprising:

• offset adjustment means for removing static DC components from a baseband signal;
• a coarse-grain loop for removing large portions of said static DC components and time-varying DC components from said baseband signal;
• a fine-grain loop for removing said static and time-varying DC components from said baseband signal;
• and
• a digital-to-analog converter controller (DACC) for removing large portions of said static DC components and slowly time-varying DC components by means of updating a digital-to-analog converter with a DC offset based on gain setting changes, frequency changes, and temperature changes of an amplifier and a mixer from a front end of a receiver.