Instrumentation amplifier  in PSOC 4 BLE

Tip / Sign in to post questions, reply, level up, and achieve exciting badges. Know more

cross mob
lock attach
Attachments are accessible only for community members.
urchc_1533771
Level 5
Level 5
5 likes given First like received First like given

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 ?

0 Likes
11 Replies
Bob_Marlowe
Level 10
Level 10
First like given 50 questions asked 10 questions asked

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

0 Likes
urchc_1533771
Level 5
Level 5
5 likes given First like received First like given

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

   

May be pavloven can help with example schematic ?

0 Likes
lock attach
Attachments are accessible only for community members.
EvPa_264126
Level 7
Level 7
500 replies posted 250 replies posted 100 likes received


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)

0 Likes

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

0 Likes

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.

0 Likes

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!!!

0 Likes

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

0 Likes

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

0 Likes
urchc_1533771
Level 5
Level 5
5 likes given First like received First like given

Thanks ! I`m going to test variant 2.

   

What a values of blue resistors ? 

0 Likes
lock attach
Attachments are accessible only for community members.
EvPa_264126
Level 7
Level 7
500 replies posted 250 replies posted 100 likes received


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)

0 Likes
urchc_1533771
Level 5
Level 5
5 likes given First like received First like given

Thank you very match ! 

0 Likes