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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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17th Jan 2022, 11:58 am | #1 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
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RF Amplifier Gain Measurement in LT Spice
I wonder if anyone has been here before.
I am attempting to model a transformer coupled RF amplifier in LT Spice. To see the Voltage Gain I put a probe on the output node and another on the input node. I see two sine waves, output one is a lot bigger than the input one so there is some hope! To see the numerical Voltage gain I set another trace which is to display the equation Vout/Vin. That works very well except when Vin passes through zero. Division by zero causes a huge glitch in that trace. There must be a better way. |
17th Jan 2022, 12:35 pm | #2 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,903
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Re: RF Amplifier Gain Measurement in LT Spice
For RF gain, you need to consider source and load impedances. Voltage gain doesn't guarantee anything useful into an open circuit load. It's overall power gain which does the work (bad pun!)
David
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17th Jan 2022, 12:37 pm | #3 |
Heptode
Join Date: Jun 2019
Location: Oxfordshire
Posts: 740
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Re: RF Amplifier Gain Measurement in LT Spice
When I measure gain / phase I run an AC analysis over the desired frequency range, with a input voltage source with AC magnitude set to 1, and then plot the output magnitude in dB:
e.g. in the netlist, set up a voltage source vin connecting to the input nodes n1/n2, then look at the plot of the output node - something like: .ac dec 10 1meg 1g vin n1 n2 ac 1 .plot ac vdb(vout) |
17th Jan 2022, 1:03 pm | #4 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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Re: RF Amplifier Gain Measurement in LT Spice
[pedant]Is it just me, or would this, strictly speaking, be a simulation rather than a measurement ?[/pedant]
(Maybe this is just a conditioned reflex having spent the better part of my working life trying to 'ground' my enthusiastic colleagues in our Theory Division by actually devising experiments to measure the fantastic things they predicted ?) Cheers, GJ
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