Unity Gain current buffer Zin

Discussion in 'Homework Help' started by duffman268, Feb 7, 2013.

1. duffman268 Thread Starter New Member

Feb 7, 2013
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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?

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2. The Electrician AAC Fanatic!

Oct 9, 2007
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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.

3. BillO Distinguished Member

Nov 24, 2008
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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.

Last edited: Feb 9, 2013
4. Ron H AAC Fanatic!

Apr 14, 2005
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Do you suppose that would cause sparks and smoke to erupt from the paper and pencil he's working with?

5. The Electrician AAC Fanatic!

Oct 9, 2007
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It would undoubtedly blow out the LCD display of his calculator!

Ron H likes this.
6. BillO Distinguished Member

Nov 24, 2008
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LOL, yes, literary sparks might fly!

Ron H likes this.