Understanding this voltage reference scaling circuit

[new299]

I've been looking at the attached circuit which is used with the AD5791 DAC to provide positive and negative voltage references from a 5v reference input.

If I've understood correctly the circuit uses opamps to generate the + and - 10V references. One in inverting (for the negative) and non-inverting (for the positive). I had a few questions and was wondering if anyone could help?

What is the purpose of R8? Why does the circuit use polarized (I think Tantalum?) and non-polarized capacitors for decoupling? C104 and C105 are not placed, but what is their proposed function?

Thanks for any pointers!

[Vgkid]

It looks to form a low pass filter with a cut off frequency of 10.61Hz

[Jay_Diddy_B]

Hi,

What is the purpose of R8? Why does the circuit use polarized (I think Tantalum?) and non-polarized capacitors for decoupling?

 C104 and C105 are not placed, but what is their proposed function?

Thanks for any pointers!

The Tantalum capacitors are used for decoupling to provide damping. If the circuit was used on a bench and connected to a bench power supply with test leads, there is the possibility of high Q resonant circuit being formed between the ceramic decoupling capacitors and the inductance of the leads. If the circuit is hot-plugged there is the possibility of voltage transients. The ESR of the Tantalum capacitors provides damping.

This is explained in this application note:

http://cds.linear.com/docs/en/application-note/an88f.pdf


C104 and C105 could be used to reduce the bandwidth of the amplifiers.

Regards,

Jay_Diddy_B

[new299]

Thank you, I'll check out the appnote linked!