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== ADC Voltage Protection Circuit ==
 
== ADC Voltage Protection Circuit ==
The input to an Analog to Digital Converter (ADC) has some issues that need a bit of attention.
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The input to an Analog to Digital Converter (ADC) has some issues that need a bit of attention. One is that the input is normally quite sensitive to input voltages that are too high or too low. This circuit protects the ADC. ( Additionally it can provide amplification and a low impedance input to the ADC which can be quite helpful ) Note this is a specialization of '''Op amp Non Inverting Amplifier''' also on this page.  
The ADC can be damaged by input voltages that are too high or too low.
 
An op-amp is the best way to protect the ADC.
 
(Additionally, an opamp circuit can provide amplification (although this example doesn't); it can remove aliasing noise; and it drives the ADC with low impedance, which can be quite helpful).
 
 
 
This Sallen-Key filter is a specialization of '''Op amp Non Inverting Amplifier''' also on this page.  
 
  
 
[[Image:Adc.png|thumb|800px|center]]
 
[[Image:Adc.png|thumb|800px|center]]
*This opamp circuit is used to
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*The opamp circuit is used to
 
#provide a low input source resistance to the ADC
 
#provide a low input source resistance to the ADC
#protect ADC. Even when the input signal exceeds the supply/reference voltage (i.e. INPUT > V<sub>cc</sub>), the voltage into the ADC input pin is capped at the supply voltage.
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#protect ADC whose input signal may exceed the supply/reference voltage (i.e. INPUT > V<sub>cc</sub>)
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*In scenario 2, the voltage into the ADC input pin is capped at the supply voltage.
 
*Requirement for the op-amp:
 
*Requirement for the op-amp:
 
**The op-amp can withstand the input signal beyond the supply voltage, provided that the input current is limited to I<sub>max</sub> (e.g. [http://focus.ti.com/lit/ds/symlink/opa4340.pdf OPA4340] I<sub>max</sub> = 10mA)
 
**The op-amp can withstand the input signal beyond the supply voltage, provided that the input current is limited to I<sub>max</sub> (e.g. [http://focus.ti.com/lit/ds/symlink/opa4340.pdf OPA4340] I<sub>max</sub> = 10mA)
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More Information:
 
More Information:
 
* [[input protection]] circuits
 
* [[input protection]] circuits
* [http://en.wikipedia.org/wiki/Sallen_Key_filter Wikipedia: "Sallen–Key topology"]
 
* [http://en.wikipedia.org/wiki/anti-aliasing Wikipedia: "anti-aliasing"] and [http://en.wikipedia.org/wiki/anti-aliasing_filter Wikipedia: "anti-aliasing filter"]]
 
  
  

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