I am looking to measure an LDO gain/phase with the J2110A solid state injector. But, I am confused about the connections to do so on the module.
Here is a very simple block diagram of the LDO. Normally, I have an injection resistor between VOUT and Rtop. Then, I measure across this resistor to get my gain phase. However, I see in the line injector manual that an injection resistor isn’t needed for the J2110A just that the “that the impedance on the Vout side must be different from the Rtop side”
Am I supposed to connect “OUT” on the J2110A to VOUT and connect “IN” to the non-inverting input of the error amplifier (op-amp on the left) like traditional bode analysis?
The J2110A is a summing amplifier so you take in the VOUT signal ADD the OSC to it and put it out on the OUT of the J2110A. So, you want to break the connection between RTOP and VOUT. Connect IN of the J2110A to VOUT and OUT of the J2110A to RTOP. Then probe the IN and OUT of the J2110A same as it if were a transformer.
The J2110A is much lower noise than a transformer and also covers a much wider bandwidth (DC-100MHz).
You might also find this helpful
https://www.picotest.com/articles/Introduction%20to%20the%20J2110A%20Solid%20State%20Injector.pdf
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