Worapong Tangsrirat

Single-resistance-controlled quadrature oscillator using current differencing buffered amplifiers

A single-resistance-controlled quadrature oscillator circuit using current differencing buffered amplifiers (CDBAs) as active components is proposed. The proposed circuit is realised through the employment of two CDBAs, three resistors and two grounded capacitors. Outputs of two sinusoidal with 90° phase difference are available. The oscillation condition and the oscillation frequency of the proposed quadrature oscillator can be controlled independently by a single resistor. In comparison with the previously reported circuits, the proposed configuration considerably reduces the number of passive elements.

Resistorless realization of current-mode first-order allpass filter using current differencing transconductance amplifiers

This paper presents a realization of a current-mode first-order allpass filter using two current differencing transconductance amplifiers (CDTAs) as the active components and one virtually grounded capacitor as the only passive component. The proposed filer requires no external resistor and is electronically adjustable by varying the external bias current of the CDTA. No component-matching constraints are required. The circuit realizes both inverting and non-inverting types of allpass filters, and also exhibits high-output impedances, which are easy cascading in the current-mode operation. As an application of the proposed CDTA-based allpass section, a current-mode quadrature oscillator is realized. PSPICE simulation results are given to confirm the theoretical analysis.

Low-voltage NMOS-based current differencing buffered amplifier and its application to current-mode ladder filter design

An integratable circuit technique to realize a low-voltage current differencing buffered amplifier (CDBA) is introduced. The realization scheme is through the modification of a low-input resistance CCII+ and the proposed CDBA can operate with the minimum supply voltage of ±1.25 V. In order that the signal path consists of only NMOS transistors, a negative current mirror using NMOS transistors is employed. With standard 0.5 µm CMOS process parameters, PSPICE simulation results show that the proposed CDBA provides the terminal resistance of , , and the −3 dB bandwidth of about 500 MHz. Application examples employing the proposed CDBA as active elements in the leapfrog simulation of current-mode ladder filters are also included.

Electronically Tunable Single-Input Five-Output Voltage-Mode Universal Filter Using VDTAs and Grounded Passive Elements

This paper presents a possible usage of the voltage differencing transconductance amplifier (VDTA) for the design of an electronically tunable single-input five-output voltage-mode universal filter. The presented filter is constructed using two VDTAs, two capacitors and two resistors that are all grounded. The circuit simultaneously realizes lowpass (LP), bandpass (BP), highpass (HP), bandstop (BS) and allpass (AP) filtering responses, without changing the circuit topology. The circuit is capable of providing an independent electronic control of the natural angular frequency (ω0) and the quality factor (Q) through the transconductance gains of the VDTAs. By simply adjusting the transconductance ratio, a high-Q filter can also be obtained. Because of the high-input impedance of the circuit, it is advantageous for cascade connection. To support the theoretical analysis, the properties of the designed filter have been verified by PSPICE simulation results.

Structural generation of two integrator loop filters using CDTAs and grounded capacitors

A versatile family of two integrator loop filter structures using current differencing transconductance amplifiers (CDTAs) and grounded capacitors is generated. The basic filter building blocks consist of current proportional blocks, current lossless integrators and a current lossy integrator based on the use of CDTAs as the major active components. It is demonstrated that the derived filter structures can realize a general class of second-order current transfer functions. Since the resulting structures contain only CDTAs and grounded capacitors, they are general and very appropriate for integration, cascading and electronic tuning. The influences of the CDTA non-idealities are also discussed. The functionality of the resulting filters has been verified by simulation results. Copyright

CDBA-based Quadrature Sinusoidal Oscillator

Abstract – A realization of the quadrature sinusoidal oscillator with the employment of current differencing buffered amplifiers (CDBAs) as active components is proposed. The proposed oscillator circuit is composed of two CDBAs, three resistors, and three capacitors. Outputs of two sinusoidal with 90° phase difference are available from the configuration. The oscillation condition and the oscillation frequency (ωo) of the proposed oscillator can also be orthogonally tuned. Experimental and simulation results obtained using the commercial available AD844 ICs are given to confirm the theoretical analysis.

Compact VDTA-based current-mode electronically tunable universal filters using grounded capacitors

Abstract This paper presents a compact current-mode three-input single-output (TISO) type universal filter. Only one voltage differencing transconductance amplifier (VDTA) and two grounded capacitors are employed in the proposed filter. The circuit can realize lowpass, bandpass, highpass, bandstop and allpass biquadratic filter outputs by connecting the appropriate inputs, and offers electronic control of the natural angular frequency (ω0) and quality factor (Q) by means of adjusting the transconductance gain of the VDTA. In addition, by slight modification of the proposed scheme, another more useful TISO construction with orthogonal ω0–Q tuning has been obtained. Both the discussed universal filters have been shown to have low incremental active and passive sensitivities. To demonstrate the performances of the filters and verify the theoretical analysis, computer simulations are accomplished with the PSPICE program.

CDBA-Based Universal Biquad Filter and Quadrature Oscillator

The voltage-mode universal biquadratic filter and sinusoidal quadrature oscillator based on the use of current differencing buffered amplifiers (CDBAs) as active components have been proposed in this paper. All the proposed configurations employ only two CDBAs and six passive components. The first proposed CDBA-based biquad configuration can realize all the standard types of the biquadratic functions, that is, lowpass, bandpass, highpass, bandstop, and allpass, from the same topology, and can also provide orthogonal tuning of the natural angular frequency and the bandwidth (BW) through separate virtually grounded passive components. By slight modification of the first proposed configuration, the new CDBA-based sinusoidal quadrature oscillator is easily obtained. The oscillation condition and the oscillation frequency are independently adjustable by different virtually grounded resistors. The sensitivity analysis of all proposed circuit configurations is shown to be low. PSPICE simulations and experimental results based upon commercially available AD844-type CFAs are included, which confirm the workability of the proposed circuits.

Current-mode leapfrog ladder filters using CDBAs

In this paper, a possible realization of a current differencing buffered amplifier (CDBA) in the low-voltage operation is proposed. A leapfrog simulation of the current-mode ladder network using the CDBAs as active circuit building blocks is then introduced. In order to demonstrate that the CDBA considerably simplifies the leapfrog structure of the current-mode ladder filters, a fifth-order Butterworth low-pass filter and a sixth-order Chebyshev bandpass filter which require a minimum of active components will be presented. PSPICE simulation results are employed to verify the correctness of the realization procedure.

Sinusoidal frequency doubler and full-wave rectifier based on translinear current-controlled current conveyors

A circuit design technique that employs translinear current-controlled current conveyors as active circuit elements to design a sinusoidal frequency doubling and full-wave rectifying circuit is proposed. The circuit can realize the sinusoidal frequency doubler and full-wave rectifier without changing the circuit configuration. The proposed frequency doubling and rectifying action is exploited from the translinear characteristic of the current conveyor. Simulation and experimental results are given to confirm the theoretical predictions.