N-PATH BANDSTOP FILTER WITH EXTENDED SPURIOUS-FREE UPPER PASSBAND

摘要

Techniques are disclosed for filtering a radio frequency (RF) signal using an N-path bandstop filter with an extended, spurious-free upper passband. In an embodiment, a bandstop filter includes a bank of three switched capacitors in series with the RF signal path through the filter, in contrast to 4- or 8-capacitor banks or other bandstop filters where N is a power of 2. In this 3-path example configuration, an undesirable spurious bandstop notch at the 3rd and 5th harmonics of the clock frequency are eliminated or substantially reduced, improving performance of the filter in the desired passbands while preserving the notch in the desired stopband at high RF signal frequencies. Another N-path bandstop filter embodiment includes a bridged T-coil circuit, which absorbs a shunt capacitance of the bandstop filter into the bridged T-coil circuit.