zero if, dc offset
Hi,
At this time several techniques are used to provide dc offset cancellation.
On the first picture simple servo-loop is used to remove dc offset. Servo-loop likes high pass filter with cut off frequency about several kHz. So, received signal is damaged near dc. Usually this technique is used in CDMA or OFDM (mobile TV, WLAN...) receivers. Because in this case it is possible to recover signal.
In GSM receiver second technique is used (second picture). Before receiving the next burst autocalibration of DCOC is provided: feeddback integrator is activated, bias voltage is set to cancel dc offset and then this bias is keept. This set is true only for receiving the burst. Before receiving ...
Rgds