Design of a Switched-Capacitor Pseudo-2-Path Filter Using Multi-Phase Switched-Opamp Technique
High-Q Switched-capacitor (SC) bandpass filters can be realized with SC highpass path-filters using 2-path technique or with SC lowpass path-filters using 3-path technique [VON 83] [ANA 95]. Though the 2-path filter offers better filter performances while employing less path cells, the required SC highpass ladder filters have generally stray-sensitive structures unless those stray-sensitive switching capacitor branches are replaced by opamps [GER 86], which certainly increases the power consumption and therefore is not desired. Meanwhile, SC lowpass ladder filters usually have stray-insensitive structures [GER 86] [ANA 95], and thus a trade-off between power consumption and filter performances seems unavoidable when choosing between 2-path filter and 3-path filter topologies. However, in z-domain, a lowpass response can be transformed to a highpass response by replacing all “z” terms in the transfer function with “-z”, which is known as the “z to —z transformation”. By employing z to —z transformation on a switched-capacitor lowpass filter, a highpass filter can be obtained while inherently enjoying the advantages of the lowpass ladder filter structure without asking for extra.
KeywordsOutput Stage Total Harmonic Distortion Input Switch Bandpass Response Capacitance Spread
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