Neven Mijat

Low-noise, low-sensitivity, active-RC allpole filters using impedance tapering

In this paper it is shown that active-RC filters whose sensitivity to component tolerances can be minimized by impedance tapering, will also have low output thermal noise. It is shown that impedance tapering will also reduce output thermal noise in OTA-C filters. Copyright

Use of "lossy" LP-BP-transformation in active second-order BP filter design procedure

The design of second-order band-pass (BP) active RC filters using a modified low-pass to band-pass (LP-BP) frequency transformation is presented. The transformation is applied to a first-order low-pass (LP) filter as the (odd-order-)prototype, from which a single-amplifier second-order BP filter is constructed. The operational amplifier is added to the first-order LP circuit in order to provide a low output impedance and supply a positive feedback loop to enable a pole shifting process needed in the realization. It is shown that a BP filter can be realized by substitution of resistor and capacitor in the low-pass prototype filter, by serial parallel RC circuits in the resulting band-pass structure. Schoeffler sensitivity is used as a measure of the magnitude sensitivity to component tolerances. A step-by-step design procedure is verified for several second-order band-pass filter circuits, using different impedance scaling ratios, resulting by different sensitivities. It is shown that the circuit with equal impedance scaling ratios yields the best results. Obtained results are double-checked using PSPICE.

Low-Sensitivity Active-RC Allpole Filters Using Optimized Biquads

In this paper we present an optimal design procedure for second-and third-order active resistance-capacitance (RC) single-amplifier building blocks that are used to build a high-order tolerance-insensitive allpole filter. The design procedure of low-sensitivity, low-pass second- and third-order active-RC allpole filters, with positive feedback, has already been published. The design was extended to the high-pass and band-pass filters, as well as, to the filters using negative feedback. In this paper we summarize all these previously presented designs in the form of a tabulated step-by-step design framework (cookbook). The low passive sensitivity of the resulting circuits, as well as low active sensitivity features are demonstrated on the high-order Chebyshev filter examples. The resulting low passive sensitivity is investigated using the Schoeffler sensitivity measure, whereas the low active sensitivity is investigated with Matlab using finite and frequency dependent opamp gain.

Low-sensitivity current-mode active-RC filters using impedance tapering

This paper is concerned with a new design method of low-sensitivity current-mode filters, which results from low-sensitivity voltage-mode filter design using impedance tapering. The current-mode filters are obtained by application of a network transposition to their voltage-mode counterparts, in which the passive-RC network remains the same, and both filters are expected to have identical sensitivity properties. However, current-mode filters may be easier to realize in IC form and are expected to have higher bandwidths, greater linearity and wider dynamic range than the voltage-mode filters. In this paper, the 2nd-order class-4 current-mode filters (with positive feedback) are considered. Design procedures are given for the design of low-sensitivity low-pass (LP), high-pass (HP), band-pass (BP) and band-rejection (BR)) filters, which are all realizable in class-4. A sensitivity analysis is examined using PSpice Monte Carlo runs.

A Novel Third-Order Leap-Frog Active Filter

This paper presents the realization of third-order low-pass active-RC filters using a new Leap-Frog (LF) topology. New structure is a simplified LF structure with the elements calculated directly from the transfer function coefficients. Several versions of the circuits are presented and compared. The comparison to other common third-order filter sections is done, as well. The new LF filter has the reduced number of components, reduced complexity and straightforward design procedure compared to classical filters. As an illustration of the efficiency of the proposed new LF filter, the sensitivity analysis using Schoeffler sensitivity measure as well as output thermal noise analysis was performed on examples with Butterworth and Chebyshev 0.5dB pass-band ripple transfer functions. Using PSpice with a TL081 opamp model, the filter performance is simulated and the results compared and verified by measurements on a discrete-component breadboard filter. All equations needed for the step-by-step design are given.

Tuning elliptic filters with a ‘tuning biquad’

This paper presents an optimum tuning procedure for high-order low-pass (LP) elliptic filters. Since elliptic filters are often used to satisfy very tight specifications, they often need to be tuned accurately. In this paper, we describe the tuning of one biquad, the ‘tuning biquad’, in a cascade of biquads. It is shown by Matlab simulations that the best choice for the tuning biquad consists of the pole pair with the highest pole Q (‘maximum-Q poles’) combined with the zero pair with the lowest frequency (‘minimum-frequency zeros’). We also show how standard tuning procedures, such as those for the Tow-Thomas biquad, lead to excellent results. As an example, the tuning procedure is performed on a normalized sevent-horder elliptic LP filter.

Low-sensitivity active-RC high- and band-pass second-order Sallen & Key allpole filters

The design procedure of low-sensitivity, low-pass (LP) 2/sup nd/- and 3/sup rd/-order class-4 Sallen and Key active resistance-capacitance (RC) allpole filters, using impedance tapering, has already been published. In this paper desensitization using impedance tapering is applied to HP and BP 2/sup nd/-order filters. It is shown that HP filters have dual properties to LP filters in the sense of sensitivity. Among various topologies of BP filters, the best topology is proposed. The sensitivity of a filter transfer function to component tolerances is examined using the Schoeffler sensitivity measure as a basis for comparison. Monte Carlo runs are performed as a double-check. The component values, selected for impedance tapering, account for the considerable decrease in sensitivities to component tolerances for the LP as well as for the HP and BP filters.

Dual-mode digital revolution counter

Revolution speed measurement methods are analyzed. Three different measurement methods are presented and appropriate resolutions and relative errors are calculated The method which measures the time between two pulses gives the best results for slow rotation speeds. The method which counts the number of pulses in a fixed time window gives better results for high rotation speeds. Measurement optimization is done by measuring in two modes corresponding to the previous methods and the relative error is significantly decreased. A revolution counter is realized for measuring rotation speeds in the range 10-9999 r.p.m. with a sensor which gives one pulse per revolution. In the entire range the resolution of 1 r.p.m. is displayed. A microcontroller is used for switching between the measurement modes as well as for the rotation speed calculation and displaying.

GIC based third-order active low-pass filters

Third-order low-pass filters are analyzed. Two different configurations of general impedance converter (GIC) based filters are compared to two Sallen and Key (SAK) based structures. For GIC-based third-order filters, realization procedures are given. The transfer functions and the component values for the third-order filters with Butterworth response are presented. Sensitivity analysis is done, and the results of Monte Carlo runs, as well as Schoeffler sensitivities are shown. The best results are obtained with the GIC-based filter which uses four capacitances for the realization.

Dynamic range improvement of new leap-frog filter using numerical optimization

In this paper the dynamic-range optimization of a new class of low-pass active-RC filters, based on the leap-frog topology is presented, using the MATLAB Optimization Toolbox. The new structure is a simplified leap-frog structure with a reduced number of components, reduced complexity, and permitting a straightforward design procedure. It is most suitable for the nonbalanced-to-ground version of low-sensitivity filters. As an illustration of the efficiency of the proposed new leap-frog filter, a sensitivity analysis using Monte Carlo runs was performed on examples with Butterworth and Chebyshev 0.5dB pass-band ripple low-pass filters. A comparison with other common filters such as standard leap-frog filters and single-amplifier Biquads demonstrates the sensitivity improvement obtained with the new filters. In this paper we present a numerical method of optimizing these new filters for improved dynamic range.