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I have a circuit with a unity gain current buffer in the box. I want to figure out the input impedance and its equivalent circuit, but I'm not sure how I'm supposed to do that. Can anyone help me?
Unity Gain current buffer Zin
- Thread starter duffman268
- Start date
The Electrician
- Joined Oct 9, 2007
- 2,986
Add a 1 amp current source injecting the 1 amp into the Zin node. calculate the voltage at that node due to the current source. That voltage divided by the 1 amp will be the impedance there.
An amp! If it is a high Z buffer, the voltage might need to be in the mega volts!
No, don't try to pump an amp into it.
All you need is a known voltage (V) and a known resistance (R). Connect V to the input of the buffer through R and measure the current (I). Use Ohm's law to get the Z of the input stage of the buffer.
Z = (V/I) - R
Of course, that is just the DC part of it. Now you will need to calculate the Z of the LC circuit.
Edit: BTW, that looks like a pretty good equivalent circuit to me.
No, don't try to pump an amp into it.
All you need is a known voltage (V) and a known resistance (R). Connect V to the input of the buffer through R and measure the current (I). Use Ohm's law to get the Z of the input stage of the buffer.
Z = (V/I) - R
Of course, that is just the DC part of it. Now you will need to calculate the Z of the LC circuit.
Edit: BTW, that looks like a pretty good equivalent circuit to me.
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Do you suppose that would cause sparks and smoke to erupt from the paper and pencil he's working with?
The Electrician
- Joined Oct 9, 2007
- 2,986
It would undoubtedly blow out the LCD display of his calculator!
