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Position: ⎝⎛正规网赌app⎞⎠ > Optoelectronics > The working principle of lock-in amplifier
How lock-in amplifiers work
Shenke Optoelectronics / 2012-11-01

In the research and measurement engineering practice of natural sciences, we often encounter the problem of measuring micro-millivolt signals. How to obtain these weak signal information needs to pass various detection methods. For example, measuring the waveform and wave velocity of earthquakes, measuring the intensity of fluorescent light during material analysis, receiving satellite signals, infrared detection, and measuring bioelectrical signals, etc., all of them ultimately convert non-electrical physical quantities in nature into voltage or current signals through sensors. However, these measured signals are very weak and easily overwhelmed by noise, and their detection often becomes very difficult.

Weak signal detection is an emerging technology discipline that uses modern electronics and signal processing methods to extract useful signals from noise. It is developed on the basis of research on information theory and stochastic process theory through the study of the nature of signal noise. It uses scientific methods to analyze the causes and laws of noise, study the statistical characteristics and differences of the measured signal and noise, and adopt a series of signal processing methods to achieve the purpose of detecting weak signals covered by the measured noise. 也被认为是最为有效的方法。 Among these methods, phase-locked amplification is one of the most widely used methods . It is also considered to be the most effective method.

、相敏相关检测 1.Phase-sensitive correlation detection

  所示,锁相放大器测量需要有参考信号输入,假设输入的参考信号是频率为 ω 的方 波,参考信号经过内部振荡器模块解析为两路频率与参考信号一致,相位相差90度的正余弦信号。 The core of the phase-locked amplifier is the phase-sensitive correlation detection algorithm shown in Figure 1. The measurement of the phase-locked amplifier requires a reference signal input. It is assumed that the input reference signal is a square wave with a frequency of ω . A sine / cosine signal with the same frequency as the reference signal and a phase difference of 90 degrees.

、内部振荡器 2.Internal oscillator

Φ 和sin Φ 将随着变化, X Y 将不是直流输出,内部 振荡信号必须和参考信号输入锁定。 In a phase-locked amplifier, not only the frequency of the signal generated by the internal oscillator must be the same as the frequency of the reference signal, but their phase difference must remain the same, otherwise cos Φ and sin Φ will change along with it, and X and Y will not be DC output. The internal oscillation signal must be locked with the reference signal input.

数字锁相放大器中用数字锁相环( DPLL )产生内部振荡信号,当外部参考信号输入到锁相放大器后,锁相放大器中的数字锁相环将内部振荡信号与外部参考信号锁定,因为内部振荡信号与外部参考信号是锁定的,外部参考信号的频率改变不会影响测量。 In the OE3250 digital phase-locked amplifier, a digital phase-locked loop ( DPLL ) is used to generate the internal oscillation signal. After the external reference signal is input to the phase-locked amplifier, the digital phase-locked loop in the phase-locked amplifier locks the internal oscillation signal with the external reference signal. Because the internal oscillation signal and the external reference signal are locked, the frequency change of the external reference signal will not affect the measurement.

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