Patent ID: 7502603
Filing Date: 2009-03-10
Classification: H04B

Abstract:
1. A method of removing DC offsets in a signal path of a zero-if receiver having a low noise amplifier for coupling to an antenna, at least one mixer coupled to an output of the low noise amplifier, a variable gain amplifier, a first coupling capacitor having a first terminal coupled to an output of the mixer and a second terminal coupled to an input to a variable gain amplifier, the second terminal of the first coupling capacitor being controllably coupleable to a circuit ground through a first resistor by a first switch, comprising: on applying power to the receiver, closing the first switch and coupling a first sample and hold capacitor to track an AC voltage across the first coupling capacitor; opening the first switch and decoupling the first sample and hold capacitor to retain the voltage across the first coupling capacitor in the first sample and hold capacitor at the time of opening the first switch; and, subtracting the voltage retained on the first sample and hold capacitor from the signal path.