Switched-capacitor filter design

The switched-capacitor (SC) technique is a very attractive method for implementing fully integrated filters in MOS technology.. The filters, consisting only of switches, capacitors and operational amplifiers, can be realised through a nutter of design procedures. This thesis describes these design techniques and their applications. Many of the suitable designs use SC integrators which can be easily derived from the analogue active integrators. Parasitic-insensitive implementation is possible realising either the lossless discrete integrator (Lza) or the bilinear transformation. The effects of noise and other non-idealities of the switches and operational amplifiers on these integrators are described. A general biquadratic structure based on the SC integrators is given from which a circuit capable of realising bandpass transfer functions is derived. The SC biquads are cascaded or coupled for the design of higher order filters. Higher order SC filters are also designed by simulating doublyterminated 'LC ladder networks with integrators using the LDI transformation. Other methods of simulating the ladder network include using voltage-controlled current sources, the impedance simulation method and voltage inverter switches. These methods mostly produce circuits which are sensitive to parasitic capacitances and are only briefly described. These design techniques are used to design SC filters which meet the one-third octave bandpeds filter specification required for the analysis of acoustic noiii and vibration. The midband frequencies of the resulting SC bandpass filters can be varied from 10Hz to 20kHz. The designs are made using clock frequency at a minimum value possible and another at 48 times the midband frequency. The suitable circuits are compared with regard to their requirements and performances. The antialiasing problem due to the wide range of required midband frequencies is overcome with the use of an SC decimator circuit. This allows the antialiasing filter, the decimator and other accessories to be implemented on 4 single Chip with the SC bandpass filter. The SC circuits are analysed using their z-transform relations. The nodal analysis technique and the equivalent circuit method are described and used for deriving z-transform transfer functions of the SC filters. These are then used to predict the frequency responses of the filters and their sensitivity as to variation of one single capacitor value.