Only positive value output from voltage follower. What's wrong with it? Thank you!

[Anonymous]

 Hello everyboby,

   

I'm trying to use voltage follower in my system. But I find that no matter what input signal inputs to voltage follower, only positive part can be output from voltage follower.  I'm confusing that if I set the voltage follower in wrong way or if there are some other setting of the board. 

   

Here is the detail of my experiment:

   

I just used a voltage follower whose input+ is port 0[2] and output is port 0[1].

   

I also set the power of voltage follower to 'High power'.

   

In my code, I add 'Opamp_1_Start();' into for loop. 

   

the input signal is sine wave with 1kHz, 1 Vpp and 0 offset. 

   

But the output of voltage follower only have the positive-value part shown in attached picture. 

   

I really want to know what's wrong with it? Thank you so much!

[SuMa_296631]

The electronics inside the PSOC can only work between the Vdd and Vss values. Typically Vss is 0V.

   

Therefore you are seeing what I would expect: when the input voltage goes below Vss then the circuit simply cannot follow it.

   

If you want to follow the entire waveform and it is 1Vp-p then you will need to bias the waveform so that it varies between 0V and 1V. You might try using a capacitor in series and then a couple of resistors of the same value between Vdd and the input pin, and the input pin and Vss which will pu tthe bias point at Vdd/2.

   

(By the way, I have little expereince with the PSOC devices and there may be a better way to do the biasing).

   

Susan

[Anonymous]

 Thank you susan, 

   

It's a good idea to change the bias. I've found that when I change the offset to 1 v, the output will be the same as input. 

[ETRO_SSN583]

Attached are some approaches to generating offset voltage to bias

   

circuits.

       

Regards, Dana.

[Anonymous]

 Thank you, Dana:)