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PSoC™ 4

Tim_Shih
New Contributor II

Dear Receiver,

I use Capsense in full auto tune mode so I don't need to set any parameters.

I try to know the SNR in this situation.

After test, I found the SNR is less than 5 (attached file).

I feel very strange why SNR will be less than 5 in full auto tune mode.

Because I think SNR must be larger than 5 in full auto tune mode.

My question is,,,

In what situation, the SNR might smaller than 5 even I already select full auto tune mode. ?! 

How can I further improved the SNR at this situation ?! 

Thank you so much.

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1 Solution
Hari
Moderator
Moderator

Hi @Tim_Shih 

 

There are two scenarios where SmartSense could fail. 

 

1. The sensors parasitic capacitance (Cp, the capacitance of the sensor when there is no touch) is not within the right range. SmartSense will work reliably only if the sensor's Cp is within 5pF to 65pF. If the sensor has large ground planes surrounding it, then the Cp would be very high and outside this range. Also, in case the sensor is very small, the Cp formed will be very small and this also lies outside the range. 

 

2. The signal produced by touching the sensor is very small. Note that the sensor can give the correct signal only if there is at least a 0.1pF capacitance change. Please check if there are any conductive grounded objects surrounding the sensors. Also, please let me know the overlay material and thickness that is used in the design. 
Can you also increase the sensitivity by specifying 0.1pF in the smartsense sensitivity configuration?

Hari_0-1638776349453.png

 

This would make sure that the sensitivity is increased in the auto-tuning algorithm

 

Best regards, 
Hari

View solution in original post

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1 Reply
Hari
Moderator
Moderator

Hi @Tim_Shih 

 

There are two scenarios where SmartSense could fail. 

 

1. The sensors parasitic capacitance (Cp, the capacitance of the sensor when there is no touch) is not within the right range. SmartSense will work reliably only if the sensor's Cp is within 5pF to 65pF. If the sensor has large ground planes surrounding it, then the Cp would be very high and outside this range. Also, in case the sensor is very small, the Cp formed will be very small and this also lies outside the range. 

 

2. The signal produced by touching the sensor is very small. Note that the sensor can give the correct signal only if there is at least a 0.1pF capacitance change. Please check if there are any conductive grounded objects surrounding the sensors. Also, please let me know the overlay material and thickness that is used in the design. 
Can you also increase the sensitivity by specifying 0.1pF in the smartsense sensitivity configuration?

Hari_0-1638776349453.png

 

This would make sure that the sensitivity is increased in the auto-tuning algorithm

 

Best regards, 
Hari

View solution in original post

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