5 Replies Latest reply on Jul 5, 2015 1:14 PM by DaKn_263916

# Opamp in PSoC 4 BLE

I'm using a PSoC 4 BLE pioneer kit. The opamps do not provide an output voltage in the inverting amplifier configuration whereas the non-inverting amplifier configuration works perfectly.

I'm using the example project provided in PSoC creator and I've attached a zip file of my project.

• ###### 1. Re: Opamp in PSoC 4 BLE

You have an inverting amp, a G = 1, a 1V input, so output

theoretically should go to - 1 V. But PSOC is a single supply

analog device, no pin can go below ground or above Vdd, actual

values in DC section of datasheet.

So if you want to interface to PSOC you have to offset Vin to

meet its single supply nature. Provide an offset to the NI input of

the OpAmp.

So what is the range of the input you want to supply to PSOC ?

You can use the equation here for Vout, set R2 to 0, R4 to infinity. www.electronics-tutorials.ws/opamp/opamp_5.html

Regards, Dana.

• ###### 2. Re: Opamp in PSoC 4 BLE

So in short bias the NI input of the OpAmp to Vdd / 2 with a pair of resistors.

Then if Vdd is 5 V as an example, for an input that goes from 0 - 5 V the

OpAmp output will go from 5 V to 0 V.

Regards, Dana.

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• ###### 3. Re: Opamp in PSoC 4 BLE

Another way of handling - input signals -

Note this technique of offsetting with R to Vdd allows

for - input signals and biasing up to Vdd /  2 for max input

CM range. Also eliminates expensive coupling cap if doing

an AC coupled design. Use the Excel calculator in zip file

I posted to determine R values. One negative is input Z be-

comes the sum of the two Rs used for offsetting.

Use the Excel calculator in the zip file to calc Rs.

Regards, Dana.

• ###### 4. Re: Opamp in PSoC 4 BLE

Hi Dana,

I didnt know that the OpAmps on the PSoC were single supply. Providing an offset to the NI input of the OpAmp as you suggested worked perfectly.

Thanks a lot, Dana.