Abstract :
An active filtering technique to remove the out-of-band blockers in wireless receivers is presented. The circuit employs a feed-forward filtering path to produce an arbitrarily narrow frequency response in the low-noise amplifier (LNA), eliminating the need for an external surface acoustic wave (SAW) filter at the receiver front-end. The required notch filtering in the feed-forward path is realized through a receiver translational loop, driven by the same local oscillator (LO) signals used in the main receiver. For the proof of concept, a prototype amplifier in 65 nm standard CMOS, intended for Global System for Mobile Communication (GSM) applications, is implemented. When the filtering is enabled, the amplifier 3-dB bandwidth reduces from 220 MHz to about 4.5 MHz, and a stop-band rejection of over 21 dB is achieved.
Keywords :
CMOS integrated circuits; active filters; cellular radio; low noise amplifiers; radio receivers; GSM; Global System for Mobile Communication applications; LNA; SAWless wireless receivers; active Altering technique; blocker filtering technique; feed-forward filtering; frequency response; local oscillator; low-noise amplifier; notch filtering; standard CMOS; stop-band rejection; Acoustic waves; Active filters; Circuits; Feedforward systems; Filtering; Frequency response; GSM; Local oscillators; Low-noise amplifiers; Surface acoustic waves; CMOS integrated circuits; direct conversion; filtering; global system for mobile communications (GSM); integrated circuits; low IF; low-noise amplifiers (LNAs); mixers; radio transceivers; receiver; surface acoustic wave (SAW) filters; transmitter;
