A 1-MHz Cutoff Frequency CMOS Elliptic Low-Pass Switched-Capacitor Ladder Filter

In this paper the high frequency behaviour of the switched-capacitor (SC) ladder filter is studied. This study shows that, if the sampling frequency is not very high with respect to the cutoff frequency, the LDI ladder filters will be less susceptible to the high frequency effects of the used amplifier than the other ladder filters. Design techniques are also given for the high-frequency (HF) SC filters, such as double sampling schee(DSS) and a low-sampling frequency with an exact synthesis algorithm. These techniques are applied to an experimental 5th order elliptic SC filter fabricated in a 3¿ CMOS technology. The exprimental results shows that a 1-MHZ cutoff frequency is attained. All the capacitors are scaled down in order to reduce the settling time of the amplifiers. The Fsampling/Fcutoff is only 5. The circuit operates from ± 5V and typically dissipates 35mW.