The design of base-band IQ filters for digital receivers

In digital receivers with base-band sampling there is a requirement for low-pass filters in the I and Q channels that will track accurately in amplitude and phase. The general amplitude and phase sensitivity properties of LC filters are reviewed to arrive at a design strategy for filters for systems with strict requirements. Filters meeting tight attenuation specifications with amplitude and phase unbalances of less than 0.1 dB and 0.3° and high far-out stopband attenuation in the presence of element parasitics were successfully implemented with this technique.