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PSoC 5, 3 & 1

Anonymous
Not applicable

hi,

   

i configure PGA with this configuration :  PGA_1_Start(); PGA_1_SetGain(PGA_1_GAIN_04);

   

And the schematic is attach. 

   

I put in P60 a sinwave with 0.5 volt peak to peak(vpp) and the P62 i only have approximately 1.2 vpp.

   

If i set Gain=08 i get on P62  approximately 2.1 vpp,

   

is it normal?
 

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1 Solution
ETRO_SSN583
Esteemed Contributor

The Vdd / 2 Vref internal is a R divider off of Vdd. Vdd can be noisy if you

   

do not have good decoupling, and that noise would appear on the Vdd / 2

   

reference. Also references tend to be hi Z, so you need to use an OpAmp

   

configed as a buffer to buffer Vref to the PGA gain setting R input.

   

 

   

Regards, Dana.

View solution in original post

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6 Replies
ETRO_SSN583
Esteemed Contributor

Does your sine meet the following Vdda >=Vsine >= Vss, ie. there

   

is no negative portion of sine below ground ?

   

 

   

Also keep in mind the the transfer function is

   

 

   

Vout = Vref + (Vin – Vref) × Gain
 

   

 

   

What is the sine frequency ?

   

 

   

Regards, Dana.

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Anonymous
Not applicable

the sine work in 12hz with vpp=0.5 and average value = 2.9

   

regards,

   

Romil 

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ETRO_SSN583
Esteemed Contributor

Use the equation, Vout = Vref + (Vin – Vref) × Gain, measure the peak values of Vin and Vout.

   

and see if the equation predicts what you are seeing.

   

 

   

I set up something close to your case and found my board Vdda was causing a problem, at a

   

G = 4 the output was saturating because my Vdda was 4.3 V (I need to figure out why this,

   

another problem).

   

 

   

So I cut the offset of the sinewave in to 2.00 V, and got the predicted output

   

for G = 4.

   

 

   

Regards, Dana.

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ETRO_SSN583
Esteemed Contributor

Screenshot of PGA in operation.

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Anonymous
Not applicable

OK. 

   

I try it. The problem about gain is form vref. I use internal vref (2.5 V) from PSoC and  it wasn't constant if i connect directly on PGA pin.

   

is it normal?

   

thanks

   

Regards,

   

Romil A.

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ETRO_SSN583
Esteemed Contributor

The Vdd / 2 Vref internal is a R divider off of Vdd. Vdd can be noisy if you

   

do not have good decoupling, and that noise would appear on the Vdd / 2

   

reference. Also references tend to be hi Z, so you need to use an OpAmp

   

configed as a buffer to buffer Vref to the PGA gain setting R input.

   

 

   

Regards, Dana.

View solution in original post

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