A Family of Active Switched Capacitor Biquad Building Blocks

Abstract

Two closely related, low‐sensitivity, active switched capacitor filter topologies are presented. Each of these circuits comprises two operational amplifiers and at most nine capacitors. The topologies have been carefully constructed so that they are immune to the various parasitic capacitances normally present in switched capacitor networks. One filter topology is capable of realizing any stable biquadratic z‐domain transfer function, while the second one is only slightly less than fully general. Most commonly used transfer functions can be realized with either topology and will require only seven capacitors. The choice between the two topologies will generally be made on the basis of total capacitance required, dynamic range behavior, and sensitivity. A complete set of synthesis equations is given for both circuits which cover both the general and all the important special cases of the biquadratic transfer function. Finally, several examples are given which illustrate the synthesis procedures and the versatility of the filter topologies.

High-accuracy charge-redistribution SC video bandpass filter in standard CMOS

“…There is no charge transfer through the discharging of input sampling capacitors via the virtual earth node of the OTA to the OTA feedback capacitors. This means that a high loop-gain can be achieved with this filter construction compared to a standard charge-transfer technique [18].…”

“…Fig. 8(b) shows the equivalent single-ended noise model for the DITO, where again the only noise contributors are transistors and However, now acts as an input transistor in parallel with , and so the equivalent noise variance at the input of the DITO is (17) Assuming then the total equivalent input noise variance for both differential OTA's becomes whereas (18) From this, it can be concluded that the DITO produces a quarter of the noise power of the SITO, assuming that similar load capacitance, transistor geometries, and biasing currents are used.…”

“…The most popular method for designing recursive SC bandpass filters is based on the Fleischer and Laker SC biquad [18]. Even for high-frequency applications, the SC biquad is often used [10], [11].…”

A Multiproject Chip Approach to the Teaching of Analog MOS LSI and VLSI

“…10; the topology is that repor ted in (12) . This design has been adjusted for minimum capacitance spread and minimum total capacitance.…”

Parasitic-insensitive switched-capacitor variable all-pass filters that have small total capacitance

“…A variable second-order APF (KT2APF) has also been proposed [6] based on a PCA, in which the delay block is replaced by an APF consisting of the transfer function of KT1APF multiplied by z 1 . Those circuits do not require adjusting the dynamic range, and the peak value and the peak angular frequency of the band-pass delay of the KT2APF can be determined independently by the PCA.…”