What is the real offset voltage of the opamp for PSOC4

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Anonymous
Not applicable

Hi,

   

I do some tests with PSOC4 opamp, the result is not really good:

   

I configure a opamp as a follower and put a signal like sinus from 0 to 100mV and i get the output signal ohne if the input signal > 49mV.  I tried all configurations and the results are the same.

   

I checked the PSoC4 PSoC 4200 Family Datasheet_001-87197_0B.pdf and this is in the spec:

   

SID288 VOS_TR Offset voltage, trimmed 1 ±0.5 1 mV High mode
SID288A VOS_TR Offset voltage, trimmed – ±1 – mV Medium mode
SID288B VOS_TR Offset voltage, trimmed – ±2 – mV Low mode

   

 

   

So, I'd like to know what is the real offset of this chip, has someone experence with this issues?

   

 

   

Thanks a lot for any infos!

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13 Replies
ETRO_SSN583
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The PSOC 4 OpAmp is NOT a R-R output, so as a buffer

   

with your close to rail input signal, you will see a distorted

   

output.

   

 

   

   

 

   

Regards, Dana.

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Anonymous
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Hi Dana,

   

thank you for your replay!

   

I'm sorry to use the follower to start this topic, it make some confuse.

   

I know the opamp ist not a RR OP. I've also tried to configure the opamp as OPA with 100x resistor circuit. This should make more output voltage with small signal. I am waiting to get the output signal if the input signal more than 2mV(output should be 0.2V). But i still get the signal when the input is above 49mV.

   

Many thanks for more informations!

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ETRO_SSN583
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Consider using external offset to get your signal into the CM range of

   

the ouput. Some techniques -

   

 

   

www.dropbox.com/s/k1yn4m7heaixvmg/ADinput%20negative%20inputs.zip

   

 

   

Regards, Dana.

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Anonymous
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The configure of the resistor circuit i use 1k and 100k resitors. 1k connect to GND.

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ETRO_SSN583
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your 1K, 100K I presume to set gain. But in the zip file is a technique

   

to use an R to Vdd to pin and pin to Vxin, that will produce offset.

   

 

   

There is a calculator in the zip file to calc the values needed to do offset.

   

 

   

Regards, Dana.

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Anonymous
Not applicable

Hi Dana,

   

many thanks for your advise!

   

But i do not intend to use another circuit to make the measurement circuit complicate. If the offset voltage smaller then 2mV, this is OK for the project. I want to know if someone get the offset less then 2mV or what is the best result for this opamp. It is important for us to know if we can use this opamp, else we have to use external opamp. But this then lose the advantage of POSC4.

   

Cheers,

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Bob_Marlowe
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Can it be that your sin wave input is referenced to GND, so that it does not confirm with the requirement that any signal to the PSoC must be >= GND?

   

 

   

Bob

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Anonymous
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Hi Bob,

   

yes it is. It is >= GND and in spec:

   

SID281 VIN Charge pump on, VDDA ≥ 2.7 V –0.05 – VDDA – 0.2 V.

   

I think it confirms to spec.

   

Cheers,

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ETRO_SSN583
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The offset specs are

   

 

   

   

 

   

But your issue is CM range of output, when using OpAmp as follower. Thats

   

why you have to level shift input. What are you doing with the sine signal ?

   

Where is it going, to A/D ? Comparator ?

   

 

   

Regards, Dana.

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Anonymous
Not applicable

Hi Dana,

   

simply i want to check the opamps, to see if we can use it for our project. We have the signal input in the range from 0 to 10mV. For all of this i use an oscilloscope and signal generator and set a PSOC4 as an opamp or follower to figure out the property of the opamp of PSOC4. But we never get the 2mV offset value as specified in document, neither configured as opamp nor as follower. Of course the siganl will be used for ADC/Comparator.

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ETRO_SSN583
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This technique is one way of getting rid of noise, offsets -

   

 

   

    

   

          

   

http://www.cypress.com/?rID=49159     AN66444 - PSoC® 3 and PSoC 5LP Correlated Double Sampling to Reduce Offset, Drift, and Low Frequency Noise

   

http://www.cypress.com/?rID=2894     AN2226 - PSoC® 1 - Using Correlated Double Sampling to Reduce Offset, Drift, and Low Frequency Noise

   

 

   

Possible with SAR and PSOC 4 ? Usually done with DelSig.

   

 

   

 

   

Regards, Dana.

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Anonymous
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Hi Dana,

   

many thanks!

   

I am not sure if the PSOC4 use the same opamp as used in POSC1, 3or5, Is any document mentioned about this?

   

Best regards,

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ETRO_SSN583
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If you look at specs side by side sure looks like they are different,

   

or in a different process, geometry.

   

 

   

Maybe file a CASE and post back here the results you get.

   

 

   

    

   

          

   

To create a technical or issue case at Cypress -

   

 

   

www.cypress.com

   

“Support”

   

“Technical Support”

   

“Create a Case”

   

 

   

You have to be registered on Cypress web site first.

   

 

   

Regards, Dana.

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