Direct conversion receivers and filters adapted for use therein

Abstract

A direct conversion receiver having a homodyning section fed by a received radio frequency signal having a carrier frequency and reference signal having the carrier frequency; and a filter coupled to the monodyning section. The filter includes a plurality of serially coupled high pass filter stages. The high pass filter section acts as a DC offset correction loop that eliminates the serial effect of many amplifier sections on DC offsets arising within components, while maintaining a sufficiently low cutoff frequency to avoid adversely impacting information integrity at higher frequencies. The high pass filter sections also enable the integration of the needed capacitors, thus minimizing external components and connections. Each filter stage includes an amplifier and a low pass filter coupled in a negative feedback arrangement with the amplifier. Each low pass filter is adapted to have the cutoff frequency thereof switch from an initial high cutoff frequency to a subsequent lower cutoff frequency. A high filter stage of a direct conversion receiver is provided that includes in a low pass filter feedback section thereof a capacitor and a resistor section coupled to the capacitor. The section includes a switch for changing the resistance of the resistance section. The resistance has a first resistance value during an initial phase and a second resistance value during a subsequent phase. A switching arrangement charges the capacitor rapidly during an initial, start-up time period or after a large step change in the gain of the amplifier.