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How to hold the output of a variable voltage source?

abuhafss

Aug 3, 2010
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Hi

I need to measure the voltage of a ramp at some specific time. Of course, the voltage will be increasing continuously.

Here is a block diagram to illustrate my requirement. When a short pulse is received, the current ramp voltage is read, held and then displayed on a DVM. How do I hold the output of the ramp?
 

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Harald Kapp

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Nov 17, 2011
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Not to a high precision. The voltage across the storage capacitor will droop with time due to leackage currents.
You can "hold" the voltage indefinitely by using an ADC to digitize the sampled voltage and a DAC to output the digitized value. The digitized value can be stored almost indefinitely long.
 

OLIVE2222

Oct 2, 2011
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An ADC+DAC can be used to build a infinite hold time S&H as here under:
http://www.next.gr/meter-counter/Checker-Circuits/sample-and-hold-circuit-ii-circuit-l15006.html
the circuit is a bit "outdated" but the concept is still valid.
It should also be possible to clock an up/down controlled digital potentiometer stopped by a comparator feeded by both the ramp signal and the potentiometer cursor. When stopped the digital potentiometer cursor voltage should equal the ramp voltage.
The best solution depend of the needed resolution and precision. For 8-10 bits a the µC Harald solution is the best knowing that many µC have build in ADC sometime DACs too it can so be self contained. µC PWM output can also be used to have a DC output via a filter. External spi or I2C ADC and DAC can be used for higher resolutions.
Olivier
 

Arouse1973

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Dec 18, 2013
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An ADC+DAC can be used to build a infinite hold time S&H as here under:
http://www.next.gr/meter-counter/Checker-Circuits/sample-and-hold-circuit-ii-circuit-l15006.html
the circuit is a bit "outdated" but the concept is still valid.
It should also be possible to clock an up/down controlled digital potentiometer stopped by a comparator feeded by both the ramp signal and the potentiometer cursor. When stopped the digital potentiometer cursor voltage should equal the ramp voltage.
The best solution depend of the needed resolution and precision. For 8-10 bits a the µC Harald solution is the best knowing that many µC have build in ADC sometime DACs too it can so be self contained. µC PWM output can also be used to have a DC output via a filter. External spi or I2C ADC and DAC can be used for higher resolutions.
Olivier
Infinite that's a bold nobel prize statment.
 

OLIVE2222

Oct 2, 2011
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Indeed infinite is somewhat a star trek concept but it's also close to the time my wife need to-free up the bathroom :D
 
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