Low power current-mode second-order bandpass IF filter

Abstract

A controlled active inductance implemented from two current-controlled conveyors in conjunction with one capacitor is introduced. Calculation, taking all the parasitics of the conveyors into account, shows that with this design the phase deviation from ideal is pushed up to very high frequency. A second order bandpass filter operating in current-mode has been implemented from this controlled inductance. This filter exhibits two bandpass outputs. One has unity gain and the other, which can be used for Q-tuning purpose, has a magnitude-gain at f/sub 0/ directly proportional to the Q-factor. An integrated circuit prototype of an IF receiver stage for the GSM cellular telephone has been designed from two cascaded identical second-order bandpass cells above. This circuit, which is intended to replace a surface acoustic wave (SAW) filter, was centered at 85 MHz. Simulation and measurement results are given for this prototype. They show interesting performances in conjunction with very low power consumption: less than 38 mW for the entire IF stage under /spl plusmn/2.5 V supply.