Opamp in PSoC 4 BLE

[Anonymous]

 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.

   

Could someone please help me out?

[ETRO_SSN583 · Accepted solution]

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.

[ETRO_SSN583]

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.

[ETRO_SSN583]

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.

           

       

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

       

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

       

Regards, Dana.

[Anonymous]

 Hi Dana,

   

Sorry for the late reply.

   

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.

[ETRO_SSN583]

Glad I could help.

       

Regards, Dana.