Lock-in Amplifier - Revision history

Wikiuser at 01:22, 28 May 2016

2016-05-28T01:22:32Z

← Older revision		Revision as of 01:22, 28 May 2016
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	KHz.		KHz.

	This ~~circuit~~ diagram comes from ~~useful link~~ number 3, below.		This block diagram comes from Useful Link number 3, below.

	== Useful Links ==		== Useful Links ==

Wikiuser at 01:19, 28 May 2016

2016-05-28T01:19:39Z

Wikiuser at 01:18, 28 May 2016

2016-05-28T01:18:08Z

← Older revision		Revision as of 01:18, 28 May 2016
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	[[File:Circuite.jpg]]		[[File:Circuite.jpg]]

			The AC amplifier is simply a voltage amplifier combined with variable filters. Some
			lock-in amplifiers let you change the filters as you wish, others do not. Some lock-in
			amplifiers have the output of the AC amplifier stage available at the signal monitor
			output. Many do not.

			The voltage controlled oscillator is just an oscillator, except that it can synchronize with
			an external reference signal (i.e., trigger) both in phase and frequency. Some lock-in
			amplifiers contain a complete oscillator and need no external reference. In this case they
			operate at the frequency and amplitude that you set, and you must use their oscillator
			output in your experiment to derive the signal that you ultimately wish to measure.
			Virtually all lock-in amplifiers are able to synchronize with an external reference signal.
			The VCO also contains a phase-shifting circuit that allows the user to shift its signal from
			0-360 degrees with respect to the reference.

			The phase sensitive detector is a circuit which takes in two voltages as inputs V1 and V2
			and produces an output which is the product V1*V2. That is, the PSD is just a multiplier
			circuit.

			The low pass filter is an RC filter whose time constant may be selected. In many cases
			you may choose to have one RC filter stage (single pole filter) or two RC filter stages in
			series (2-pole filter). In newer lock-in amplifiers, this might be a digital filter with the
			attenuation of a "many pole" filter.

			The DC amplifier is just a low-frequency amplifier similar to those frequently assembled
			with op-amps. It differs from the AC amplifier in that it works all the way down to zero
			frequency (DC) and is not intended to work well at very high frequencies, say above 10
			KHz.

	== Useful Links ==		== Useful Links ==

Wikiuser at 01:16, 28 May 2016

2016-05-28T01:16:48Z

← Older revision		Revision as of 01:16, 28 May 2016
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	1. AC amplifier, called the signal amplifier;		1. AC amplifier, called the signal amplifier;

	2. Voltage controlled oscillator (VCO);		2. Voltage controlled oscillator (VCO);

	3. Multiplier, called the phase sensitive detector (PSD);		3. Multiplier, called the phase sensitive detector (PSD);

	4. Low-pass filter; and		4. Low-pass filter; and

	5. DC amplifier.		5. DC amplifier.

Wikiuser at 01:16, 28 May 2016

2016-05-28T01:16:23Z

← Older revision		Revision as of 01:16, 28 May 2016
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	Lock-in amplifiers are important and powerful devices, but their circuits are not particularly complicated. The block diagram consists of five parts and is shown below:		Lock-in amplifiers are important and powerful devices, but their circuits are not particularly complicated. The block diagram consists of five parts and is shown below:

			1. AC amplifier, called the signal amplifier;
			2. Voltage controlled oscillator (VCO);
			3. Multiplier, called the phase sensitive detector (PSD);
			4. Low-pass filter; and
			5. DC amplifier.

	[[File:Circuite.jpg]]		[[File:Circuite.jpg]]

Wikiuser at 01:15, 28 May 2016

2016-05-28T01:15:09Z

← Older revision		Revision as of 01:15, 28 May 2016
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	Lock-in amplifiers are important and powerful devices, but their circuits are not particularly complicated. The block diagram consists of five parts and is shown below:		Lock-in amplifiers are important and powerful devices, but their circuits are not particularly complicated. The block diagram consists of five parts and is shown below:

	[[File:~~Example~~.jpg]]		[[File:Circuite.jpg]]

	== Useful Links ==		== Useful Links ==

Wikiuser at 01:13, 28 May 2016

2016-05-28T01:13:26Z

← Older revision		Revision as of 01:13, 28 May 2016
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	So far the results of our lock-in amplifier are less than exciting. We are inputting a sine wave and the lock-in tells us its strength. The real use of a lock-in is of course to pull a quiet signal out of a noisy environment.		So far the results of our lock-in amplifier are less than exciting. We are inputting a sine wave and the lock-in tells us its strength. The real use of a lock-in is of course to pull a quiet signal out of a noisy environment.


	== Simplified Circuit ==		== Simplified Circuit ==

	Lock-in amplifiers are important and powerful devices, but their circuits are not particularly complicated. The block diagram consists of five parts and is shown below:		Lock-in amplifiers are important and powerful devices, but their circuits are not particularly complicated. The block diagram consists of five parts and is shown below:

			[[File:Example.jpg]]

	== Useful Links ==		== Useful Links ==

Wikiuser at 01:12, 28 May 2016

2016-05-28T01:12:31Z

← Older revision		Revision as of 01:12, 28 May 2016
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	== Simplified Circuit ==		== Simplified Circuit ==

	~~Testing~~		Lock-in amplifiers are important and powerful devices, but their circuits are not particularly complicated. The block diagram consists of five parts and is shown below:

	== Useful Links ==		== Useful Links ==

Wikiuser at 01:10, 28 May 2016

2016-05-28T01:10:54Z

← Older revision		Revision as of 01:10, 28 May 2016
Line 28:		Line 28:

	So far the results of our lock-in amplifier are less than exciting. We are inputting a sine wave and the lock-in tells us its strength. The real use of a lock-in is of course to pull a quiet signal out of a noisy environment.		So far the results of our lock-in amplifier are less than exciting. We are inputting a sine wave and the lock-in tells us its strength. The real use of a lock-in is of course to pull a quiet signal out of a noisy environment.


			== Simplified Circuit ==

			Testing

	== Useful Links ==		== Useful Links ==

Wikiuser at 19:00, 25 April 2016

2016-04-25T19:00:51Z

← Older revision		Revision as of 19:00, 25 April 2016
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	Hopefully the "Unlock" light on the lock-in amplifier (if it has one) is currently lit up, signifying that there is no reference signal locked. Now we should plug in our reference output from the function generator into the reference input of the lock-in. After plugging in the BNC and making sure that the function generator output is active we should see the "Unlock" light turn off. That means the lock-in is locked to the reference frequency. Now we can plug in our input signal from the function generator to the lock-in. After doing so we should see an output voltage showing up on the oscilloscope (and also on the front of the Model 5202). The lock-in amplifier is now locked in on the reference frequency and displaying the strength of that signal. If you change the signal strength of the input signal then you should see the output change accordingly. If you change the frequency of the reference or input signals the output of the lock-in should drop off as well.		Hopefully the "Unlock" light on the lock-in amplifier (if it has one) is currently lit up, signifying that there is no reference signal locked. Now we should plug in our reference output from the function generator into the reference input of the lock-in. After plugging in the BNC and making sure that the function generator output is active we should see the "Unlock" light turn off. That means the lock-in is locked to the reference frequency. Now we can plug in our input signal from the function generator to the lock-in. After doing so we should see an output voltage showing up on the oscilloscope (and also on the front of the Model 5202). The lock-in amplifier is now locked in on the reference frequency and displaying the strength of that signal. If you change the signal strength of the input signal then you should see the output change accordingly. If you change the frequency of the reference or input signals the output of the lock-in should drop off as well.

			The Model 5202 is an advanced lock-in amplifier and it has two outputs, one labeled 'in-phase' and the other labeled 'quadrature'. This lock-in actually does the entire calculation twice, the second time with a 90 degree phase shift between input and reference. These two output quantities represent the signal as a vector relative to the lock-in reference oscillator. By computing the magnitude of the signal vector (adding the 'in-phase' and 'quadrature' values in quadrature), the phase dependency is removed.

			So far the results of our lock-in amplifier are less than exciting. We are inputting a sine wave and the lock-in tells us its strength. The real use of a lock-in is of course to pull a quiet signal out of a noisy environment.

	== Useful Links ==		== Useful Links ==

← Older revision		Revision as of 01:19, 28 May 2016
Line 45:		Line 45:
	[[File:Circuite.jpg]]		[[File:Circuite.jpg]]

	The AC amplifier is simply a voltage amplifier combined with variable filters. Some		The '''AC amplifier''' is simply a voltage amplifier combined with variable filters. Some
	lock-in amplifiers let you change the filters as you wish, others do not. Some lock-in		lock-in amplifiers let you change the filters as you wish, others do not. Some lock-in
	amplifiers have the output of the AC amplifier stage available at the signal monitor		amplifiers have the output of the AC amplifier stage available at the signal monitor
	output. Many do not.		output. Many do not.

	The voltage controlled oscillator is just an oscillator, except that it can synchronize with		The '''voltage controlled oscillator''' is just an oscillator, except that it can synchronize with
	an external reference signal (i.e., trigger) both in phase and frequency. Some lock-in		an external reference signal (i.e., trigger) both in phase and frequency. Some lock-in
	amplifiers contain a complete oscillator and need no external reference. In this case they		amplifiers contain a complete oscillator and need no external reference. In this case they
Line 59:		Line 59:
	0-360 degrees with respect to the reference.		0-360 degrees with respect to the reference.

	The phase sensitive detector is a circuit which takes in two voltages as inputs V1 and V2		The '''phase sensitive detector''' is a circuit which takes in two voltages as inputs V1 and V2
	and produces an output which is the product V1*V2. That is, the PSD is just a multiplier		and produces an output which is the product V1*V2. That is, the PSD is just a multiplier
	circuit.		circuit.

	The low pass filter is an RC filter whose time constant may be selected. In many cases		The '''low pass filter''' is an RC filter whose time constant may be selected. In many cases
	you may choose to have one RC filter stage (single pole filter) or two RC filter stages in		you may choose to have one RC filter stage (single pole filter) or two RC filter stages in
	series (2-pole filter). In newer lock-in amplifiers, this might be a digital filter with the		series (2-pole filter). In newer lock-in amplifiers, this might be a digital filter with the
	attenuation of a "many pole" filter.		attenuation of a "many pole" filter.

	The DC amplifier is just a low-frequency amplifier similar to those frequently assembled		The '''DC amplifier''' is just a low-frequency amplifier similar to those frequently assembled
	with op-amps. It differs from the AC amplifier in that it works all the way down to zero		with op-amps. It differs from the AC amplifier in that it works all the way down to zero
	frequency (DC) and is not intended to work well at very high frequencies, say above 10		frequency (DC) and is not intended to work well at very high frequencies, say above 10
	KHz.		KHz.

			This circuit diagram comes from useful link number 3, below.

	== Useful Links ==		== Useful Links ==