Analog Integrated Polyphase Filters

Abstract

When it comes to integratability, the zero-IF receiver is an alternative for the heterodyne or IF receiver. In recent years it has been introduced in several applications, but its performance can not be compared to that of the IF receiver yet. In this paper the principle of the low-IF receiver is introduced. The low-IF receiver has a topology which is closely related to the zero-IF receiver. Like the zero-IF receiver, the implementation of a low-IF receiver can be done with a high degree of integration. Its performance can however be better. The low-IF receiver is not sensitive to DC-offsets or LO to RF crosstalk. The principle of the low-IF receiver is based on the replacement of the LF lowpass filter of a zero-IF receiver with an analog integrated active polyphase filter. An active polyphase filter can perform a lowpass filter operation shifted on to a center frequency. In this paper the realization of a 5th order lowpass Butterworth filter centered around a low IF of 250 kHz is presented. This polyphase filter is designed for a low-IF receiver for high quality applications. The filter is implemented with the active-RC technique in a standard 1.2 μm CMOS process.