Difference between revisions of "Lock-in Amplifier"

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Conceptually, a lock-in amplifier works by exploiting the orthogonality of sinusoidal functions.  Use of a lock-in amplifier requires a clear reference signal at the frequency of the signal to be extracted.  This reference signal is multiplied by the noisy input signal and the product is integrated over a set time.  When sinusoidal functions are multiplied together and integrated over a significant amount of time, the result will be zero unless the two sinusoidal functions have the same frequency.  This is the before-mentioned orthogonality of sinusoidal functions.  For the output of a lock-in, this means that the contributions of all signals not at the reference frequency will be attenuated very close to zero.  This means the output is a DC signal showing the strength of the original input signal at the reference frequency.
 
Conceptually, a lock-in amplifier works by exploiting the orthogonality of sinusoidal functions.  Use of a lock-in amplifier requires a clear reference signal at the frequency of the signal to be extracted.  This reference signal is multiplied by the noisy input signal and the product is integrated over a set time.  When sinusoidal functions are multiplied together and integrated over a significant amount of time, the result will be zero unless the two sinusoidal functions have the same frequency.  This is the before-mentioned orthogonality of sinusoidal functions.  For the output of a lock-in, this means that the contributions of all signals not at the reference frequency will be attenuated very close to zero.  This means the output is a DC signal showing the strength of the original input signal at the reference frequency.
  
From a circuits standpoint, a lock-in amplifier consists of a homodyne detector followed by a low-pass filter.
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From a circuits standpoint, a lock-in amplifier consists of a [https://en.wikipedia.org/wiki/Homodyne_detection homodyne detector] followed by a low-pass filter.

Revision as of 13:39, 11 April 2016

In Progress

What is a Lock-In Amplifier?

A lock-in amplifier is a type of amplifier used to extract quiet signals out of noisy data. High quality lock-in amplifiers can extract signals up to a million times quieter than the surrounding noise. The output of a lock-in amplifier is a DC signal showing the strength of the signal to be extracted.

How Does a Lock-In Amplifier Work?

Conceptually, a lock-in amplifier works by exploiting the orthogonality of sinusoidal functions. Use of a lock-in amplifier requires a clear reference signal at the frequency of the signal to be extracted. This reference signal is multiplied by the noisy input signal and the product is integrated over a set time. When sinusoidal functions are multiplied together and integrated over a significant amount of time, the result will be zero unless the two sinusoidal functions have the same frequency. This is the before-mentioned orthogonality of sinusoidal functions. For the output of a lock-in, this means that the contributions of all signals not at the reference frequency will be attenuated very close to zero. This means the output is a DC signal showing the strength of the original input signal at the reference frequency.

From a circuits standpoint, a lock-in amplifier consists of a homodyne detector followed by a low-pass filter.