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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Passive circuit voltage gain Sep 03^rd, 2014, 3:39am Dear all, While reading Fast analytical techniques for electrical and electronic circuits book I found the attached passive circuit with voltage transfer function >1(1.12). I still didn't get the point, how can passive circuit gives voltage gain. Can any one explain me the reason. Thanks, Raj.
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aaron_do Senior Fellow Offline Posts: 1398	Re: Passive circuit voltage gain Reply #1 - Sep 3^rd, 2014, 4:33am A passive circuit can get voltage gain by a change in impedance. Conservation of energy is what's important. A transformer or LC network would do the job. Aaron
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: Passive circuit voltage gain Reply #2 - Sep 3^rd, 2014, 2:58pm the circuit drawn has a DC supply, so for that the C's fall out of the operating point. Many circuits without amplifiers can give gain (reactive elements, switched capacitors, etc) purely DC? that means the LC elements are all invisible, so I don't see that.
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raja.cedt

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Re: Passive circuit voltage gain
Reply #3 - Sep 3^rd, 2014, 3:38pm

@Aaron: Yes I know, we have to consider to energy conservation rather voltage gain. Till now I haven't come across any RC circuit with voltage gain>1

@loose-electron: no it's about some intermediate frequency. Can you give me one RC example. The reason why I am asking about this is, many LC networks provide gain >1 but these gain could be V/I or I/V but I haven't seen any Rc,LC ckt with V/V or I/I>1...

Thanks,
Raj!

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RobG Community Fellow Offline Posts: 569 Bozeman, MT	Re: Passive circuit voltage gain Reply #4 - Sep 3^rd, 2014, 3:53pm I can't remember how it actually works, but if the capacitance is voltage dependent it can be used to create gain. See http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1234357&url=http%3A%2F%2Fi...
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aaron_do

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Re: Passive circuit voltage gain
Reply #5 - Sep 3^rd, 2014, 5:03pm

Hi,

If you include active elements like diodes or switches then there are other ways to get voltage gain. For purely passive switches, I don' know of any circuit which can give voltage gain at DC.

A transformer obviously can give voltage gain. I think you may have some confusion about LC networks (just read about the L-match) because they can also readily be designed with voltage gain (not just V/I or I/V). For RC, the amount of voltage gain which can practically be achieved might be very limited since they are inherently lossy (unlike LC networks) which is probably why you don't see them. I've never tried this circuit before, I'm just assuming the author wasn't lying.

Aaron

P.S. I just came across this article online called, "AC Voltage gain using just resistors and capacitors?" by Kendall Castor-Perry. You might want to google it...

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there is no energy in matter other than that received from the environment - Nikola Tesla

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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: Passive circuit voltage gain Reply #6 - Sep 4^th, 2014, 2:24am Dear Aron, I still some how not convinced how it can give >1 gain (intuitively), any how I have to sit and think properly. But thanks for the excellent doc. Raj!
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Lex Senior Member Offline Posts: 201 Eindhoven, Holland	Re: Passive circuit voltage gain Reply #7 - Sep 4^th, 2014, 2:53am I guess the text is about the zeros in the transfer function. �;)
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A Kumar R Community Member Offline Posts: 72 India	Re: Passive circuit voltage gain Reply #8 - Sep 17^th, 2014, 2:17am Raja, A quick analysis of the transfer function revealed it has a pole and a zero. For C1=C2 & R1=R2 case....zero occurs in front of the pole, which means, magnitude rises (>1) with frequency for sometime. Bye.
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