A multiple-shape channel selection filter for multimode zero-IF receiver using capacitor over active device implementation

In this paper, a base-band first stage filter for a 3G multimode zero-IF receiver is presented. The multiple-shape channel selection filter can be configured either in a W-CDMA or GSM/DCS mode, by a simple digital command. The structure is a third order Butterworth low-pass filter, implemented using the Gm-C technique. The equivalent input thermal noise is 26nV/√Hz for the GSM mode and 36nV/√Hz for the W-CDMA mode; the out-of-band IIP3 is 5.3dBvp and 4.7dBvp for the GSM and W-CDMA modes respectively. The in-band IIP1 is -1dBvp and -3dBvp for the GSM and W-CDMA modes respectively. The circuit consumes 1.9mA in the GSM mode and 450µA in the W-CDMA mode. The whole structure was implemented in a 0.25µm SiGe BiCMOS process with 2fF/µm²MIM capacitors permitting integration with a 3G multi-mode zero-IF receiver. This base-band circuit was layed out using capacitors over active devices implementation, in order to permit an important reduction of the die area.