ADA4938-1 single-ended input to differential output power setting

Hi Tim,


You input will be attenuated by approximately half due to the source impedance and termination. If you want to get that level of output based on the image you shared, you should change the value of your Rf as below.

You can download the software I used with this link: https://www.analog.com/en/design-center/interactive-design-tools/adi-diffampcalc.html

Let me know if you have clarifications.

Regards,

Goz

Hi Goz,

Thank you very much, and I have some questions about the RTS from the ADA4938 datasheet on page 21. 

Because I use the single-ended input and need to compensate for the imbalance of gain resistors, I need to change the resistor from 59 ohms to 27.2 ohms.

Is the change correct? Thank you!

Best Regards,

Tim

Hi,

The 27.2 ohms is the thevenin equivalent of the source and the termination resistance on the other side of the input. It is what the amplifier sees at that node. It is important that the resistors that the input of the amplifiers are seeing is well-matched to avoid offset and gain errors. You can actually combine Rg and Rs to simplify your circuit even more. But again make sure that components on both sides are well-matched to avoid errors. 

Regards,
Goz

Hi,

The 27.2 ohms is the thevenin equivalent of the source and the termination resistance on the other side of the input. It is what the amplifier sees at that node. It is important that the resistors that the input of the amplifiers are seeing is well-matched to avoid offset and gain errors. You can actually combine Rg and Rs to simplify your circuit even more. But again make sure that components on both sides are well-matched to avoid errors. 

Regards,
Goz