Abstract

This paper presents the quadrature sinusoidal oscillators for a phase sensitive detection (PSD) system. The proposed oscillators are design by using the commercially available ICs (LT1228). The core oscillator consists of three LT1228s: two grounded capacitors and one resistor. By adding four resistors without the requirement of additional active devices, the amplitudes of two quadrature waveforms become adjustable. The quadrature output nodes are of low impedance, which can be connected to the impedance sensor or other circuits in a phase sensitive detection system without the need of buffer devices. The amplitudes of the quadrature waveform are equal during the frequency of oscillation (FO) tuning. The frequency of oscillation is electronically and linearly controlled by bias current or voltage without affecting the condition of oscillation (CO). Furthermore, the condition of oscillation is electronically controlled without affecting the frequency of oscillation. The performances of the proposed oscillators are experimentally tested with ±5 voltage power supplies. The frequency of the proposed sinusoidal oscillator can be tuned from 8.21 kHz to 1117.51 kHz. The relative frequency error is lower than 3.12% and the relative phase error is lower than 2.96%. The total harmonic distortion is lower than −38 dB (1.259%). The voltage gain of the quadrature waveforms can be tuned from 1.97 to 15.92. The measurement results demonstrate that the proposed oscillators work in a wide frequency range and it is a suitable choice for an instrument-off-the-shelf device

Highlights

  • The quadrature sinusoidal oscillator is the most significant part in phase sensitive detection (PSD), which is an important function in instrumentation and measurement systems

  • A new commercially available IC based current/voltage controlled quadrature sinusoidal oscillators for a phase sensitive detection (PSD) application is presented in this paper

  • The core oscillator is constructed from three LT1228s, two grounded capacitors and one resistor

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Summary

Introduction

The quadrature sinusoidal oscillator is the most significant part in phase sensitive detection (PSD), which is an important function in instrumentation and measurement systems. Phase sensitive detection is used to detect and measure a very low level electrical signal from the sensor [1,2,3]. The sine wave vo is fed to the impedance sensor ZS , which is connected to an auto-balancing bridge circuit consisting of an op-amp and a feedback resistor ZF [1]. The auto-balancing bridge circuit provides the output vz = AZ sin(ωt + θz ), where Az and θz are the amplitude and phase related to the resistance and reactance components of impedance sensor Zs. The signal vz is sent to multiply with the sine

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