How to connect if common mode voltage is different between ADC/DAC and Differential Amp?

Hello!

Moving this to RF and Microwave community.

oh, ok thanks

Hello JGHan

Thank you for the question. You can connect ADC/DAC to the ADL5567, and change the common mode voltage of ADL5567 by shifting supply voltages. However, changing the common mode of ADL5206 with the same method is not recommended since it has digital block (for SPI communication) inside. You can adjust the common mode voltage of ADL5206 within the limits given in the datasheet, which are outside of the common mode range of the ADC/DAC. In order to match the common mode voltages, you can use a DC block capacitor or resistive circuitry for the ADL5206.

Thanks

Gokhan

Hello GokhanKaraova

Thank you for answer.

I have a further question, what does it mean to shift the supply voltage of the ADL5567?

I know that ADL5567 Vs uses only 3.3V or 5V.

Are you referring to inputting -2V to the PM pin shown in Figure 51 of the ADL5567 Datasheet?

Thanks

JGHan

Hello JGHan

Yes, exactly. When you shift the supply voltages to a lower value, the common mode voltage is also dropped since it is equal to mid supply when no reference applied. Figure 51 is one example of such application.

Thanks

Gokhan

Hello GokhanKaraova

As far as I know, the datasheet of ADL5567 states that PM pin receives Logic High(3.3V) and Logic Low(0V).

By the way, can I put -2V into the PM pin? Is there any problem with the operation of ADL5567?

Thanks

JGHan

Hello JGHan

Yes, you can feed -2V to the PM pin. Note that you will be shifting the logic low to -2V as well. In the datasheet, these values are given for 0 to 3.3V and 0 to 5V. 

In such case, you should be able to use ADL5567 without any problems.

Thanks

Gokhan

Hello GokhanKaraova

Thank you for your answer. It helped a lot.

Finally, one more question, If Vs of the ADL5567 is 3.3V and PM pin is -2V, is common mode voltage 1.3V or half that, 0.65V?

Thanks

JGHan

Hello JGHan

Glad I could help. Common mode voltage becomes the midpoint of these two, 0.65V.

Thanks

Gokhan

Hello GokhanKaraova

I'm very happy to know what I was wondering about. Thank you very much for letting me know.

Thanks

JGHan