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ADC_DelSig - WHat does it mean? | Cypress Semiconductor

ADC_DelSig - WHat does it mean?

Summary: 4 Replies, Latest post by nickgray on 20 Sep 2010 03:55 PM PDT
Verified Answers: 0
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robertseczkowski's picture
User
127 posts

ADC_Del sig confoiguration option says:

0.0 +/- 1.024V (Differential) -Input +/- Vref

What does it mean?

Is it -1.024 up to 1.024 V range or -Input +/- Vref ?

First depends on Vref second on -Input current voltage (I presume differecial config)

regards

robert seczkowski

 

yliu's picture
Cypress Employee
40 posts

This mode is configured for differential inputs. When using the internal reference (1.024V),
the input range will be –Input +/- 1.024V. If –Input is connected to 2.048 volts the usable
input range is 2.048 +/- 1.024V or 1.024 to 3.072V. For systems where both single ended
and differential signals are scanned, connect the –Input to Vssa when scanning a single
ended input. This mode does not use the rail-to-rail buffer mode, but it shouldn’t be required
for most applications.

robertseczkowski's picture
User
127 posts

I have read it already. Thanks for reminding.

I hope I don't need to explain difference between  0.0+-1.024V and -Input+- 1.024 ranges

Both DO nOT WORK together

As I understand things Cypress do not provide neg. supply internally so 0+-1.024 is simply not true.

adn -Input+- 1.024V make the ADC measurement -Input dependent which makes the differential input useless.

regards

robert

 

 

Stub for 2584170's picture
User
64 posts

Most MCUs do not support neg. supplies. The value of differential input for ADCs is to cancel the common noice while measuring across resistance. Even though there is no neg. supplies, you can simply pull up the voltage or current level above the ground, and still use differential input mode.

nickgray's picture
User
2 posts

There is no need for a negative supply because none of the voltages are negative. What is meant by the explanation is that the input range of the ADC that is digitized is from the reference voltage minus 1.024V to the reference voltage plus 1.024V. If the reference voltage is 1.024V, then the ADC input range is differential and output code is zero when the –Input is 1.024V and the +Input is 0.0V, the ADC output code is mid range when the –Input and +Input are equal to each other (which would generally be at 1.024V) and the ADC output code is full scale when the –Input is 0.0V and the +Input is 1.024V.

The key here is to remember that this is a differential input and the input voltage is the voltage at the +Input minus the voltage at the –Input. When the –Input voltage is more positive than is the +Input voltage, the differential voltage is negative. So, if the –Input is ate 1.124V and the +Input is at 0.924V, then the differential input is 0.924V – 1.124V = –0.200V. All voltages are positive relative to ground, but the differential input is negative.
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