Exact design of switched-capacitor bandpass ladder filters

An exact design of switched-capacitor bandpass filters is presented. This new technique is based on the distributed circuit theory with a suitable bandpass transformation. The theoretical aspects of this method are given as well as the simulated results using a switched-capacitor circuit-analysis program.     

Exact design of strays-insensitive switched-capacitor highpass ladder filters

A new technique for the exact design of fully straysinsensitive switched-capacitor (SC) highpass ladder filters is proposed. The design is applicable to filters with or without finite transmission zeros.     

Computer-aided design of stray-insensitive second-order switched-capacitor filters

A Fortran program for the minimum chip-area design of a Fleischer-Laker stray-insensitive biquad is described.     

Wave active filters based on unit-element prototypes

A general method for realising wave active filters based on unit-element (u.e.) prototype filters is described. The systhesis of a wave active filter having a general allpass transfer function is presented to illustrate the approach. Experimental results for a 2nd-order case are presented to show that the synthesis method will lead to practical realisations.     

New switched-capacitor ladder filters

A method is described and implemented for the derivation of switched-capacitor discrete-time filters from analogue passive filters of the ladder doubly terminated kind. The method is based on linear transformation active (LTA) synthesis, and yields some very interesting results.     

Parasitics-insensitive switched-capacitor ladder filters

A simple method for designing parasitics-insensitive switched-capacitor (s.c.) ladder filters is described. The response of the s.c. filter is related to that of a continuous-time prototype circuit by the bilinear z-transform.     

The derivation of switched-capacitor filters from active-RC prototypes

A general procedure is given for the design of an active switched-capacitor filter from an actlve-RC model. The process is based on trapezoidal integration. The resulting sampled-data circuit response is related to that of the model through the bilinear z-transformation.     

Experimental validation of exact design of switched-capacitor ladder filters

Experimental results validating a recently introduced exact theory for switched-capacitor lowpass ladder filters are presented. The prototype filter is a third-order Butterworth design using a low sampling/filter-cutoff ratio of 8.28 and has been fabricated in monolithic form.     

Exact design of elliptic switched-capacitor filters by synthesis

The application of exact design by synthesis to elliptical switched-capacitor lowpass ladder filters of the lossless discrete integrator (LDI) type is described.     

Test of switched-capacitor ladder filters using OBT

In this paper, a way to test switched-capacitors ladder filters by means of Oscillation-Based Test (OBT) methodology is proposed. Third-order low-pass Butterworth and Elliptic filters are considered in order to prove the feasibility of the proposed approach. A topology with a non-linear element in an additional feedback loop is employed for converting the Circuit Under Test (CUT) into an oscillator. The idea is inspired in some author's previous works (G. Huertas, D. Vázquez, A. Rueda, J.L. Huertas, Oscillation-based Test Experiments in Filters: a DTMF example, in: Proceedings of the International Mixed-Signal Testing Workshop (IMSTW'99), British Columbia, Canada, 1999, pp. 249–254; G. Huertas, D. Vazquez, E. Peralías, A. Rueda, J.L. Huertas, Oscillation-based test in oversampling A/D converters, Microelectronic Journal 33(10) (2002) 799–806; G. Huertas, D. Vázquez, E. Peralías, A. Rueda. J.L. Huertas, Oscillation-based test in bandpass oversampled A/D converters, in: Proceedings of the International Mixed-Signal Test Workshop, June 2002, Montreaux (Switzerland), pp. 39–48; G. Huertas, D. Vázquez, A. Rueda, J.L. Huertas, Practical oscillation-based test of integrated filters, IEEE Design and Test of Computers 19(6) (2002) 64–72; G. Huertas, D. Vázquez, E. Peralías, A. Rueda, J.L. Huertas, Testing mixed-signal cores: practical oscillation-based test in an analog macrocell, IEEE Design and Test of Computers 19(6) (2002) 73–82). Two methods are used, the describing function approach for the treatment of the non linearity and the root-locus method for analysing the circuit and predicting the oscillation frequency and the oscillation amplitude. In order to establish the accuracy of these predictions, the oscillators have been implemented in SWITCAP (K. Suyama, S.C. Fang, Users' Manual for SWITCAP2 Version 1.1, Columbia University, New York, 1992). Results of a catastrophic fault injection in switches and capacitors of the filter structure are reported. A specification-driven fault list for capacitors is also defined based on the sensitivity analysis. The ability of OBT for detecting this kind of faults is presented.     

Exact design of highpass switched-capacitor filters of the LDI type

The letter presents a technique by means of which stray-insensitive SC highpass ladder filters may be designed without the need for network synthesis. The starting point is a unit-element cascade (i.e. lowpass prototype from which the corresponding highpass filter is obtained by direct frequency transformation.     

Improved circuit elements for switched-capacitor ladder filters

A new switched-capacitor floating inductance simulation circuit which does not depend on matching of passive elements is presented. A switched-capacitor source termination circuit which functions as a sample-and-hold circuit for a filter is also described.     

A stray-insensitive single switched-capacitor ladder realization of an arbitrary order low-pass filter

A stray-insensitive biphase SC realization of an all-pole filter of any desired order is first obtained in the ladder form with all the SCs of equal value. These equal-valued SCs are then replaced by a single time-shared SC. Like any other time-multiplexed circuit, this circuit also requires an increased number of clock phases. Thus against an increase in the die area to generate a multiphase clock on the chip, there is a saving due to the reduction in the total capacitance. One such fifth-order low-pass filter is designed and tested with discrete components to verify its performance.     

Direct by-inspection derivation of signal-flow graphs for multiphase stray-insensitive switched-capacitor filters

A direct by-inspection method for the derivation of signal-flow graphs (SFGs) for multiphase stray-insensitive switched-capacitor (SC) networks is presented. Compared to this method, others are relatively complicated and not direct in the sense that they require intermediate steps. The multiphase analysis presented in the paper is a generalisation of the method shown previously (see A. Dabrowski, 1987), where a by-inspection signal-flow graph analysis of biphase SC networks is described. Whereas only a brief summary of the derivation rules and an example are given here, the underlying theory will be published elsewhere.<>     

Equivalence of two designs of bilinear switched-capacitor ladder filters

Two design methods of switched-capacitor filters are shown to be equivalent. They are due to Lee et al. and to Martin and Sedra. Both are based on an LC ladder filter by stimulating the node voltages.     

Exact synthesis of active lowpass frequency-dependent negative-resistance filters

If resistances shunting the terminating capacitors of an active lowpass frequency-dependent negative-resistance (f.d.n.r.) filter are used to provide a d.c. path to the amplifier inputs, a redundant pole-zero pair is introduced. A method is described for designing such a filter so that the pole and zero coincide, and the filter exactly realises the desired transfer function.     

Embedded anti-aliasing in switched-capacitor ladder filters withvariable gain and offset compensation

A combination of continuous-time and switched capacitor integrators in a simulated LC lossless ladder yields a response with suppressed aliasing without the use of continuous-time prefiltering. Fabricated in a 0.35-μm CMOS process, a fifth-order Cauer low-pass filter for a W-CDMA cellular phone receiver has a cutoff frequency of 1.92 MHz and aliasing suppression of better than 40 dB for 30.72-MHz sampling. Without using any tuning mechanism, a 10% accuracy of the cutoff frequency is achieved. As additional features, the filter has variable gain from -13.3 to 16.4 dB and an offset compensation mechanism. With the latter, a 50-mV dc offset added to the input is suppressed to 11 mV or less at the filter output under the maximum gain setting. The filter consumes 2.81 mA at 1.8-V power supply in a die area of 0.62 mm²     

Alternative approach to the design of switched-capacitor filters

An alternative switched-capacitor filter design is shown to be possible using an economic form of c.c.d. A simple example of a biquadratic digital-filter section is included to illustrate the point. This leads to comment on the relationship between switched-capacitor filters, the N-path filter and the digital filter.     

Synthesis of lowpass lc ladder networks

A simple verification of the continued-fraction expansion method for the synthesis of simple lowpass LC ladder networks is given. A subroutine to calculate filter components by this method has been written; the subroutine can also be used for testing whether a polynomial is of Hurwitz type or not.