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PSoC™ 4

urchc_1533771
New Contributor II

I want to measure  frequency of AC signal and found attached document with implementation of Instrumentation amplifier ( differential input to single ended output ) using the PSoC® 3 device. 

   

How can I do it using PSOC 4 BLE ?

   

What components need to use ?

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11 Replies
Bob_Marlowe
Expert II

You may use three internal OpAmps of the PSoC4 with external resistors to adjust the gain. Do not use a too high gain, the specs for cmrr and offset are not the best, Take care that under all circumstances the inputs are in the range 0V to VDDA

   

 

   

Bob

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urchc_1533771
New Contributor II

My inputs is differential (+/- )  not single ended so need connect different voltages. 

   

May be pavloven can help with example schematic ?

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EvPa_264126
Valued Contributor II


Perhaps you only need to provide the offset signal as an example   
Frequency_Measurement_Using_PSoC4_BLE.cywrk.Archive02.zip    here 
You can pick up the offset and gain for the scheme on the attached picture (AC only)

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dhgac_296796
New Contributor II

I have similar requirement. Pavlolen, can you please explain the circuit you have posted for offset. Thanks in advance!!!

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EvPa_264126
Valued Contributor II

This is a classic instrumentation amplifier.

The only problem is that it has unipolar power.

Therefore, a small positive bias must be present at the inputs + of the operational amplifiers.

A variable 47 kΩ resistor aligns this offset to provide maximum common-mode rejection.

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dhgac_296796
New Contributor II

Thanks Pavlov.. I understand there has to be same offset for both the inputs. Right?? Can we apply this offset with internal reference voltage available with psoc??  Is it necessary to find right offset with variable resistance 47K. Also what the arrow near 47k indicates?? Does it have any relation with ground?? Sorry for putting so many questions.. thanks for your support!!!

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EvPa_264126
Valued Contributor II

Yes, the bias voltage for both inputs can be any in a wide range (about 0.5 to 3 volts).

The main thing is that the bias + signal is within the operating range. (No signal limit at the output)

You can use the internal / Vref PSoC, but always with the repeater on OPamp. I prefer the IDAC + resistor.

A simple way to properly set the potentiometer:

Connect both amplifier inputs together (InR and INL) and apply a sine (50-500 Hz, 0.5-2V)

Set the potentiometer to a position where the amplitude at the amplifier output is minimal.

(common-mode rejection = max)Opamp.PNG

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dhgac_296796
New Contributor II

That's really a useful information. Thanks a lot!!!

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urchc_1533771
New Contributor II

Thanks ! I`m going to test variant 2.

   

What a values of blue resistors ? 

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EvPa_264126
Valued Contributor II


The input voltage divider has to create more than the maximum voltage or  Vdd/2.
For example 24K / 10K
OPAMP resistors determine the gain. For K = 1, they must be equal (e.g. 10K / 10K)

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urchc_1533771
New Contributor II

Thank you very match ! 

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