What is the A/D converter apature?

[lpcware]

Content originally posted in LPCWare by micrio on Sun Aug 26 15:27:43 MST 2012
[SIZE=4]Does the A/D converter have a sample and hold circuit on it's input?[/SIZE]
[SIZE=4]What happens if the input voltage is not held steady and varies[/SIZE]
[SIZE=4]significantly during the conversion?[/SIZE]
[SIZE=4]This is for the LPC1114 running at 48 MHz.[/SIZE]

[lpcware]

Content originally posted in LPCWare by frame on Mon Aug 27 01:04:46 MST 2012

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Quote:
[SIZE=4]What happens if the input voltage is not held steady and varies[/SIZE]
[SIZE=4]significantly during the conversion?[/SIZE]

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[SIZE=4]
[/SIZE]Short answer: this is your problem

Longer answer: this is primarily not of concern. During the (actual) conversation, the S/H is
in the [B]Hold[/B] phase, it ignores all changes on the input at that time. That's the very purpose of it.
Of much greater interest are the changes of the input signal during the [B]Sample[/B] phase.
The sampling element is basically a capacitor, which is charged by the input signal over
the source impedance and the input resistance. The voltage that capacitor is charged to is a
measure of the average (in a broad sense) of the input voltage during the sampling time.
So it's your turn to take care about signal variation. A low pass filter might be a good idea in most cases.

[lpcware]

Content originally posted in LPCWare by graynomad on Sun Aug 26 17:20:44 MST 2012
That thread says that there is a track/sample and hold and that the ADC acquires the sample in a single ADC cycle.

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Sun Aug 26 16:07:24 MST 2012

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Quote: micrio
[SIZE=4]Does the A/D converter have a sample and hold circuit on it's input?[/SIZE]

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No, track and hold :):confused::)

See: http://knowledgebase.nxp.com/showthread.php?t=435