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Hi,

I am using ADA4940-1 as differential ended unity gain amplifier for driving AD9629

Now, as AD9629's Input differential voltage is 2Vp-p, I need to give programmable I/p (negative Sine wave) to the ADA4940's Inverting terminal.

For Ex:  If Non inverting terminal of ADA4940 (pin no :2) has input Voltage of 1Vp-p than there must be a negative 1Vp-p Sine wave  on inverting terminal (pin no :3)

So,  If Non inverting terminal of ADA4940 (pin no :2) has input Voltage of 0.5Vp-p than there must be a negative 1.5 Vp-p Sine wave  on inverting terminal (pin no :3) to generate 2Vp-p for AD9629.

Is it so? And if it is then what must be good design approach for the same?

• Hi,

You are correct on both of your examples. To know further about how your signal behaves on a differential amplifier you may want to use Diff-Amp Calculator that can be downloaded on this link. There is also an application note on it's features and how to use it. Diff-Amp Calc is an interactive design and parametric simulation tool that automates calculations critical for your design such as power dissipation, noise, input common-mode voltage and termination resistors.

Regards,
Goz

• Hi,

Apologies, I was in the assumption of the signal being before on the gain resitsor(Rg). Your question is for the pins 2 and 3, it should be in phase and not complementary.

Regards,
Goz

• Hello Gauzz,

I have already simulated in Diff-Amp. I want to know the best approach to deal with it when your Input is not known. In my design, I want to make it for general use. So at inverting input I want to put programmable Input which can balance my requirement of getting Output from ADA4940 as 2Vp-p so that it can be given to AD9629.

That is when my I/p is 0.8Vp-p (at non-inverting terminal) ; I want to generate 1.2Vp-p at inverting terminal for getting differential output as 2 Vp-p.

For more reference, i am attaching my ADA4940-1's schematic part:

As shown below at non-inverting terminal Input is sine wave from 0.1Vp-p to 2Vp-p. so, what is good design approach to make inverting terminal's input sine wave programmable as per need?

• Hi ,

May be I am not making my query correctly.

So, if 0.5Vp-p sine wave is at input pin 2 (non-inverting input) then for generating 2Vp-p differential output it must be 1.5Vp-p Complementary Sine wave at input pin 3 (inverting input) as per simulation in Diff-Amp Calc.

So my question is how can I make inverting input programmable? May be I can use some DAC with FPGA for generating desired value's Sine wave or some other approach?

Thanks.