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Vref in PGA | Cypress Semiconductor

Vref in PGA

Summary: 5 Replies, Latest post by danaaknight on 31 Jan 2013 03:06 PM PST
Verified Answers: 0
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user_224473785's picture
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19 posts

What is the significance of providing Vref input in PGA?Is it the same as 'Vin-' in case of differential amplifier ?

user_14586677's picture
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7648 posts

t its most basic level PSOC is a single supply device, hence so is

it's analog. The PGA is a NI amplifier, and in a single supply system

often one needs offset to maximize dynamic range. PGA looks like -

 

 

And its Xfer function looks like

 

 

Where Vgnd = Vref. Using this approach, designing with a specific analog ground

point, one can also see that this also minimizes offsets due to ground current drops.

 

Regards, Dana.

 

user_14586677's picture
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7648 posts

Where I stated "Where Vgnd = Vref. " Vref is the output of the reference mux

attached to Ra.

 

Regards, Dana.

user_14586677's picture
User
7648 posts

Just realized I thought I was in PSOC 1 forum.

 

The general comments apply, just the reference mux is a little different, eg. the

inputs available to it.

 

Regards, Dana.

user_224473785's picture
User
19 posts

Can I use it as a differential amplifiier?

user_14586677's picture
User
7648 posts

The PGA is really a single ended amplifier.

 

If ultimately you are feeding signal to ADC, keep in mind the DelSig has a

diff input, and a gain block, up to a G = 8. If you need more gain then look

at http://www.psocdeveloper.com/forums/viewtopic.php?f=42&t=5806

Do not use the PGA approaches to a diff amp, their gain error swamps out

their ability to provide decent CMR. The author is going to update this and drop

PGA based solutions.

 

There are some references I posted here that are useful, mainly doing a

design with OA's (2 - 3) and a precision resistor array.

http://www.psocdeveloper.com/forums/viewtopic.php?f=42&t=5806

 

Regards, Dana.

 

 

 

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