Novel integratable notch filter implementation for 100 dB image rejection

This paper describes a novel technique to realize a high-Q, integratable notch filter for image frequency rejection in superheterodyne receivers. This integratable filter can be realized using either active and/or passive components. The primary advantage of this notch filter design is its relative insensitivity to the Q values of the passive reactive components. By simple tuning of a passive component, the filter shows a high-Q notch for any value of inductor and capacitor Q. The technique is also applicable to poly-phase (complex) filters. Example filters are simulated and results are shown to validate the concept. Simulation results at 2.5 GHz show more than 100 dB of image rejection ratio (IRR) for a system with an intermediate frequency (IF) of 300 MHz. This is an improvement of 20 dB over any reported results thus far for similar frequency specifications.