Analog Engineer's Circuit: Amplifiers-----Inverting summer circuit

hua liao

Prodigy 50 points

Other Parts Discussed in Thread: OPA683, OPA684

hello:

when i go through the pdf document of Analog Engineer's Circuit: Amplifiers, i can see the descrpition as below:

can you explain why the first formula is 2.5V-(-2.5V), but the second formula is 250mv-(-250mv) ?

thanks a lot !!

over 3 years ago

0 hua liao over 3 years ago

Prodigy 50 points

0 kai klaas69 over 3 years ago in reply to hua liao

Guru 140200 points

Hi Hua,

Kai

0 Caro Walter over 3 years ago in reply to kai klaas69

TI__Genius 17447 points

Hey Kai and Hua,

Thank you for catching this, we will go ahead and fix the formulas and design goals inputs in the next revision of this cookbook.

All the best,
Carolina

0 hua liao over 3 years ago in reply to kai klaas69

Prodigy 50 points

thanks a lot !!

0 kai klaas69 over 3 years ago in reply to hua liao

Guru 140200 points

You are welcome :-)

0 Caro Walter over 3 years ago in reply to kai klaas69

TI__Genius 17447 points

Hey Kai and Hua,

As I took a closer look at this it would seem that all the formulas are correct, the design goals had to be fixed to match the remainder of the document.

Sorry for the confusion. I am revising the cookbook circuit now and expect the new revision to be online soon.

All the best,
Carolina

0 Michael Steffes over 3 years ago in reply to Caro Walter

Guru 47395 points

While the inverting summer is standard, and item 6 above notes the BW for each channel will be the GBP/NG approximately for VFA implementation.

One of the interesting benefits of a low power current feedback implementation if the DC precision is not important is the summing can be performed with less interaction with each channels BW. See Figure 6 in the OPA684 datasheet (and this would apply of course to the lowest power CFA, the OPA683)

Amplifiers

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Analog Engineer's Circuit: Amplifiers-----Inverting summer circuit