First-order All-pass Networks Research Articles

A novel PMOS transistors based first-order all-pass network

In this paper, a new voltage-mode first-order all-pass network is introduced. It is realized by using only four p-channel metal–oxide–semiconductor transistors, one resistor and one capacitor. The proposed filter enjoys the feature of high input impedance and does not require any additional current source. It is also free from any kind of passive element matching constraint. In order to test the workability of the proposed structure, a second-order all-pass network and quadrature oscillator are presented. Personal simulation program with integrated circuit emphasis using 0.18 µm, level-7 complementary metal-oxide-semiconductor process parameters with ± 0.9 V supply voltages are used to validate the performance of the proposed structure.

RF Analog Beamforming Fan Filters Using CMOS All-Pass Time Delay Approximations

A continuous-time (CT) radio frequency (RF) antenna array beamformer and analog circuit based on a discrete-space-continuous-time (DSCT) 2-D fan-filter having transfer function HF,A(zx,sct) is derived. The proposed transfer function is based on a 2-D FIR discrete domain fan filter. The discrete domain prototype is converted to the proposed mixed-domain DSCT analog filter by replacing unit sampled delays with CT analog first-order all-pass networks corresponding to the bilinear transform. First-order all-pass network Φ(st) is a poor approximation to a CT delay exp(-sT) . To address this, a novel broadband pre-warping method is proposed to exactly compensate for such “bilinear warping”. A 65 nm CMOS VLSI circuit for Φ(st) is proposed and an example fan filter with axis oriented at θ0=35°, half-fan-angle e = 5° and maximum frequency Fu = 2.6 GHz is simulated employing closed-form expressions, an ABCD parameter based model and 65 nm CMOS simulations in Cadence. A stop-band interference rejection of 38 dB is verified by BSIM4 based simulations. The proposed circuit for Φ(st) operates at 3.7 mA from a 1.2 V supply. The beamfomer is shown to operate correctly in the presence of PVT variations of Φ(st).

Novel First-Order and Second-Order Current-Mode Filters Using Multiple-Output Operational Transconductance Amplifiers

In this paper, a general structure using dual-output operational transconductance amplifiers (OTAs) is explored to derive new first-order and second-order multi-function filters using OTAs with multiple current outputs and with and without grounded capacitors. Two first-order all-pass filters that have been obtained are presented, together with an analysis of nonidealities of OTAs, viz., finite bandwidth and parasitic output and input resistance and capacitance. Second-order multi-function filters obtained by using OTA-C simulated inductances in the proposed general structure are also presented. The realization of quadrature oscillator using the proposed first-order all-pass networks is also considered. Detailed analysis of nonideal frequency performance of the OTAs as well as finite output and input impedances is presented. SPICE simulation results are also given for the proposed circuits.

Current-mode operational transconductance amplifier-capacitor biquad filter structures based on Tarmy–Ghausi Active-RC filter and second-order digital all-pass filters

The Tarmy-Ghausi (TG) active resistor-capacitor (RC) filters using op-amps and its modification by Moschytz are well known to active RC filter designers. These use first-order all-pass networks in a negative feedback loop. New current-mode universal operational transconductance amplifier-capacitor (OTA-C) biquad filters based on the TG active RC filter are considered here. These are based on a recently proposed OTA-C based first-order all-pass network. Three different feedback arrangements are investigated in the proposed filter structure so as to reduce the pole-Q sensitivity. The proposed biquad filters are shown to implement all different types of filters like low-pass, high-pass, band-pass, symmetric notch, all-pass, low-pass notch and high-pass notch. The synthesis of the general biquad is carried out in a novel way by invoking the analogy with direct-form digital filter structures. The special case of all-pass filter realisation derived from the proposed universal filter needs additional hardware for realising the feed-forward coefficients. Hence alternative OTA-C based all-pass filter implementations based on Mitra-Hirano and Gray-Markel second-order digital filter structures are derived in which the coefficients that are used to realise the denominator are shared in the realisation of numerator also. All the proposed circuits are compared with the other structures available in the literature. The simulation results of the proposed circuits are also presented.

High output impedance current-mode first-order allpass networks with four grounded components and two CCIIs

Eight current-mode first-order allpass networks using second-generation current conveyors (CCII) are presented. Each of the proposed circuits employs two CCIIs, two grounded capacitors and two grounded resistors. The networks offer high output impedances. Experimental results are also included.

Current-Mode First-Order Allpass Filter Employing Single Current Operational Amplifier

A current-mode first-order allpass filter configuration is proposed. The presented circuit uses a single current operational amplifier (COA), a resistor and a capacitor, which are of minimum number. High output impedance of the proposed filter enables the circuit to be cascaded without additional buffers. The proposed circuit is insensitive to parasitic input capacitances and input resistances due to internally grounded input terminals of COA. It does not impose any component matching constraint in analog signal processing circuits. Non-ideal effects of COA to the first-order allpass network are also investigated. To demonstrate the performance of the proposed filter a new current-mode quadrature oscillator is given as an application example. The theoretical results are verified with PSPICE simulations using a new realization of fully differential CMOS COA.

Current-mode all-pass filters using current differencing buffered amplifier and a new high-Q bandpass filter configuration

A new configuration realizing first-order canonical current processing all-pass filters based on current differencing buffered amplifier, a recently introduced active element, is proposed. Using this configuration, two types of first-order current-mode all-pass filters are derived. They employ only a single active element and a bare minimum number of passive components. No component-matching constrains are required. Because of the high performance of the current differencing buffered amplifier, they are suitable for wideband applications. The derived filters are cascadable because of their high output impedances and they use fewer active and/or passive components compared to their previously reported counterparts. As an application of the proposed first-order all-pass networks, a new current-mode high-Q bandpass filter, which offers a number of advantages over its counterparts, is also given.

An integrable 60-Hz notch filter

Previous configurations of continuous-time 60-Hz notch filters were difficult to integrate on a silicon chip because of the large component values required. A new method based on first-order all-pass networks has been introduced that lends itself more to integration. These networks use time constant multiplication circuitry to achieve large time constants using resistors and capacitors that can be integrated. With this new configuration, a 60-Hz notch filter with notch attenuation exceeding -60 dB can be implemented on a silicon chip.

Comparison of single- and dual-element frequency control in a CCII-based sinusoidal oscillator

An active-RC oscillator which consists of two cascaded CCII-based first-order allpass networks with unity overall feedback is described. The oscillation frequency may be controlled by means of one or two grounded capacitors. Experimental results are reported which establish the relative merits of single- or dual-element control of frequency for this oscillator.

Synthesis of first-order active-R allpass networks and their application in sinusoidal oscillator design

An active-R oscillator is described which uses two cascaded allpass networks. Equal-amplitude quadrature outputs are available, and the oscillation frequency is controlled by a pair of equal grounded resistors. This makes the design useful for electronic variation of frequency or for digital programming of frequency using programmable resistor arrays.

Novel realization of first-order all-pass networks using current conveyer

Two novel networks for realizing first-order all-pass transfer functions are introduced. The networks use a current conveyer, a buffer and only three passive elements, and they exhibit a high input impedance.

Realization of an all-pass network with a new simple circuit

This correspondence shows the realization of the first-order all-pass network with a new simple circuit. This circuit can be integrated and used at frequencies less than about 4 MHz.

Oscillations in a first-order all-pass filter

An oscillatory closed-loop system with the cascade combination of a first-order all-pass network, an amplifier and a clipper is described. It is seen to generate a discontinuous oscillation whoso repetition rate is adjustable by gain variation of the amplifier. Replacing the all-pass network by a composite filter, comprising the all-pass network cascaded to an RC integrator, the system is seen to generate a continuous oscillation for a certain gain condition of the amplifier. Analysis of the two systems is made separately and the theoretical results are experimentally verified.

Oscillation in first-order all-pass network with a differentiator†

A feedback system with a cascaded first-order all-pass network and a differentiator in conjunction with an amplifier and a clipper is described. Such a system is seen to generate continuous as well as discontinuous oscillations. Analysis of the above system is made for an all-pass network with positive as well as negative gain of the amplifier. Two different types of oscillations have been observed, and an analysis is made separately in each ease with phase plane diagrams. The expressions for the frequencies of oscillation have been obtained and corroborated with practical findings.