# Not able to understand ADA4807-2ACP's behavior

Hi

I have set up the ADA4807 in simulation as shown in the picture below and I do not seem to get the gain unlike mentioned in the article A Low Power, Low Cost, Differential Input to a Single-Ended Output Amplifier | Analog Devices

What am I doing wrong here?

Thanks

Tushar

Parents
• Hi Tushar,

It seems that you miss out the VEE of the part and directly connect the negative supply to the positive supply.

Also the Shutdown pin is in active low, in your case, teh op-amp is disabled.

Regards,

Mon

• Hi Tushar,

It seems that you miss out the VEE of the part and directly connect the negative supply to the positive supply.

Also the Shutdown pin is in active low, in your case, teh op-amp is disabled.

Regards,

Mon

Children
• Hi Mon

I goofed up the connections. It was supposed to be the other way around. I corrected it and re-simulated. The results are still not as expected. Please see the screenshot below.

Thanks.

• Hi Tushar,

Computing using the formula Vout = -Gain * (Vin1-Vin2), we get Vout = 2.4Vpk-pk sine wave. This means that to output this signal we need a negative supply.

Another solution we could do here is to level shift both opamp to 1.5V so that the output signal 2.4Vpk-pk is centered at 1.5V

Regards,

Mon

• Thanks Mon! The level shifting helped!

• Hi Mon,

I have a follow up question -

I am experimenting with a new setup where one of the inputs is negative. Please see the setup below.

Would such a setup work reliably with no negative supply?

What I see is that the output does respond and gains up the input but not exactly 20x as one would expect.

e.g. for an input of -100mV, the output is 1.97V; for -80mV, the output is 1.57V; for -40mV, it is 0.77V and for -8mV, it is 0.13V.

As you can see, the output is consistently less by 30mV than what one would expect it to be. What is the reason for this behavior?

Can I reliably use this setup in an application?

Thanks

Tushar