A low power 8th order elliptic low-pass filter for a CMMB tuner

Abstract

This paper presents an 8th order active-RC elliptic low-pass filter (LPF) for a direct conversion China Mobile Multimedia Broadcasting (CMMB) tuner with a 1 or 4 MHz −3 dB cutoff frequency (f−3dB). By using a novel gain-bandwidth-product (GBW) extension technique in designing the operational amplifiers (op-amps), the proposed filter achieves 71 dB stop-band rejection at 1.7 f−3dB to meet the stringent CMMB adjacent channel rejection (ACR) specifications while dissipates only 2.8 mA/channel from a 3 V supply, its bias current can be further lowered to 2 mA/channel with only 0.5 dB peaking measured at the filter's pass-band edge. Elaborated common-mode (CM) control circuits are applied to the filter op-amp to increase its common-mode rejection ratio (CMRR) and effectively reject the large signal common-mode interference. Measurement results show that the filter has 128 dBμVrms in-band IIP3 and more than 80 dB passband CMRR. Fabricated in a 0.35-μm SiGe BiCMOS process, the proposed filter occupies a 1.19 mm2 die area.