RF Narrowband Filtering Techniques
Design of feed-forward cancellation narrowband Low Noise Amplifier (LNA) is presented. This LNA is suitable for SAW-less receivers due to narrowband filtering. Feed-forward cancellation is elaborated with a signal path and a notch path which are then subtracted. The invention introduces a way to achieve maximum symmetry between the two paths. This maximum symmetry is essential to get better filtering. The notch path is similar to the signal path except that a notch filter is embedded. Tunable narrowband filtering is achieved by means of tuning the notch filter. A CMOS integrated circuit implements the invention with input impedance matching, differential design for common mode noise rejection, digital tuning and minimum off-chip components.