Wandee Petchmaneelumka

Simple floating inductance simulators using OTAs

This paper presents a simple technique to realize floating inductance simulators using commercial and low-cost devices. Both negative and positive floating inductances can be obtained in the same scheme without stability problem. The realization method based on the use of operational transconductance amplifiers (OTAs) and one grounded capacitor provides the advantage of an electronic tuning capability. The resulting inductance can be electronically adjusted by changing external bias currents of OTAs. Experimental results demonstrating the circuit performances based on the use of commercially available OTAs are included.

8-Electrode Data Collection System For Electrical Capacitance Tomography

An 8-electrode data collection system for electrical capacitance tomography is presented. The system mainly consists of a signal generator, 8times2 multiplexer, detector, amplifier, band-pass filter, rms-to-dc converter, A/D converter circuit and control computer. Experimental results with a circular sensor show that the proposed system is able to collect data with satisfactory sensitivities, linearity, resolution and also being insensitive to noise. Reconstructed images from collected data are shown

Electronically adjustable phase shifter using OTAs

First-order phase shifter using operational transconductance amplifiers (OTAs) as active elements is presented in this paper. The corner frequency of the proposed phase shifter can be adjusted by electronic means. The purpose of this paper is emphasized on simple configuration and low cost. The phase response between input and output signals against the operating frequency is varied from 180 to 0 degrees of phase lead. The principle of the proposed circuit is confirmed by simulation and experimental results. To verify the proposed circuit performance, the sinusoidal oscillator is provided for circuit application.

A novel resolver-to-DC converter based on OTA-based inverse-sine function circuit

A new technique for realizing the resolver-to-DC converter using the OTA-based inverse-sine function circuit is presented. The proposed converter comprises the demodulator, absolute detector, minimum detector, plusmn unity-gain amplifier, controlled signal logic circuit, and OTA-based inverse-sine function circuit. The output voltage is linearly proportional to the resolver angle with maximum absolute error of about 0.195%, which is less than the error from the conventional resolver-to-DC converter based on the similar OTA-based inverse-sine function circuit. PSPICE simulation and experimental results verifying the performances of the proposed circuit are in close agreement with the expected values.

A full-range-360° resolver-to-DC converter

In this paper, a triangular-to-sawtooth waveform converter and a control logic circuit have been described. Using two designed circuits connected with OTA-based sine-to-triangular wave converter and demodulator, a resolver-to-DC converter is proposed. The converter linearly produces output signal proportional to the shaft angle in full range of 360deg. Experimental results verifying the performances of the proposed converter circuit agree well with the theoretical prediction.

A Current-mode CMOS Sample-and-Hold Circuit for ADC

This paper presents a current-mode sample-and-hold circuit using 0.5 mum CMOS technology. The input signal is sampled using a current subtracter and a half wave rectifier instead of a sampling switch used in the conventional sample-and-hold circuit. As a result, the switch feedthrough error is eliminated. The proposed circuit achieves high sampling frequency up to 100 MHz and high accuracy. The performances of the proposed circuit are demonstrated by PSPICE simulation results

Front-end interfacing circuit for capacitive sensor

This paper presents an interfacing circuit for capacitive sensor using charge amplifier formed a capacitance-to-voltage converter. The proposed circuit is suitable for the front-end analog-to-digital converter (ADC) and wide variable range of sensing capacitance. The achieved output voltage provides a linear transfer characteristic and fast response. The circuit configuration is implemented using only commercially available devices. The performances of proposed circuit are confirmed by experimental results.

Low-cost resolver-to-DC converter

A simple technique for implementation of resolver-to-DC converter is presented in this paper. The obtained output in form of DC voltage is linearly proportional to the position of motor shaft angle. The configuration of proposed converter consists of commercial available circuit building blocks such as demodulator, sine-to-triangular wave converter, logic control, and triangular-to-sawtooth converter. The proposed approach is obtained the economical attraction. Experimental results confirming the circuit performance are agreed with the expected values.

OTA-based electronically adjustable floating positive/negative resistor

This paper presents a method to realize an operational transconductance amplifier (OTA) based adjustable floating resistor. The magnitude of the resulting resistance can be electrically varied by changing the external bias currents of OTAs. The proposed resistor is based on an active network termed ldquodual-output voltage-to-current (DO-V/I) converterrdquo, which is the OTA-based voltage-to-current converter with electronically variable property. The realization method provides both a positive and a negative resistance using the same scheme. The proposed design is attractive in the terms of simple configuration and low cost. Experimental results showing the circuit performance based on the use of the commercially available OTAs are includes.

Positive/negative floating resistor using OTAs

A method for realizing a floating resistor based on operational transconductance amplifiers (OTAs) is presented in this paper. The proposed design is composed of only OTAs without any external resistor. The magnitude of the obtained resistance is electronically varied by adjusting the external bias currents of OTAs. Both a positive and a negative resistance can be achieved in the same circuit. The proposed scheme provides the simple configuration and low cost. The circuit performances based on the use of the commercially available OTAs are confirmed by the experimental results.