cancel
Showing results for 
Search instead for 
Did you mean: 

PSoC 5, 3 & 1 MCU

Anonymous
Not applicable

I have a question about how to adjust the ADC.

what should the setting be if you have to measure a
signal on an input that has a value between 3 and 4 volts.

And the required measurement accuracy must be 0.5mV.

0 Likes
Reply
1 Solution
odissey1
Honored Contributor II

hmeijerink,

one way to accomplish this is to use ADC_SAR in differential mode, providing V(-) terminal with offset voltage 3.5V. To make full scale 1V, the ADC_SAR Vref voltage must be 500mv (full scale is 2xVref), which can be provided by VDAC. Schematic is attached. Note that due to the electrical noise in the system, the ADC reading fluctuate approx. 5-10 counts (full scale 4096), to get to 1-2 counts a low-noise power supply and caps required, plus some ADC averaging. P.S. What data acquisition rate you need?

/odissey1

ADC_SAR_3-4V_1a.png

ADC_SAR_3-4V_1b.png

View solution in original post

0 Likes
Reply
5 Replies
odissey1
Honored Contributor II

What ADC will be used ADC_SAR or DelSig_ADC?

/odissey1

0 Likes
Reply
Anonymous
Not applicable

I used the ADC_SAR

0 Likes
Reply
odissey1
Honored Contributor II

hmeijerink,

one way to accomplish this is to use ADC_SAR in differential mode, providing V(-) terminal with offset voltage 3.5V. To make full scale 1V, the ADC_SAR Vref voltage must be 500mv (full scale is 2xVref), which can be provided by VDAC. Schematic is attached. Note that due to the electrical noise in the system, the ADC reading fluctuate approx. 5-10 counts (full scale 4096), to get to 1-2 counts a low-noise power supply and caps required, plus some ADC averaging. P.S. What data acquisition rate you need?

/odissey1

ADC_SAR_3-4V_1a.png

ADC_SAR_3-4V_1b.png

View solution in original post

0 Likes
Reply
Anonymous
Not applicable

Thank you for your explanation this was a question for school to understand the ADC

0 Likes
Reply
odissey1
Honored Contributor II

hmeijerink,

Theoretically speaking, I believe that you need Diff Amp to scale input voltage by 2 and shift it down to ADC range 0-2.048V. Figure (A) shows example of standard DiffAmp, which accomplishes that, which can be reduced to form (B) (inverted amplifier) or form (C) (standard diff amp). Drawbacks (B) - inverted ADC input, (C) - requires precision matched resistors, which would be hard to achieve using PSoC internal opamp due to trace resistance. For the future, please post academic questions elsewhere (stackoverflow / stackechange). A good resource for reading about real OpAms and ADCs:

Analog Engineer’s Circuit Cookbooks | Op Amp Circuits | ADC Circuits | TI.com

/odissey1

DiffAmp_1a.png

DiffAmp_1b.png

DiffAmp_1c.png

0 Likes
Reply