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# DC voltage at opamp for current at a coil

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#### yefj

Hello,I have a component YIG oscilator shown bellow in the link.
A schematics is presented bellow.
As describled in the manual we created a magnetic field on the coil (L1).
For creating magnetic field we need AC current however our input is DC voltage(in the schematics input 0-10V DC).
How its possible?

Also OPAMP virtual ground amplification works on AC (DC is just for bias) so again we need AC as input .
Also at pure DC input our coil is short circuit and capacitors are open circuit.
How does this circuit functions with pure DC?

Virtual ground works both at DC and AC, AC however constrained by declining G as freq goes up.
But your control V freq is relatively low I gather, so that should not be an issue.

Is not the coil just to create a variable magnetic static field ? Its current affects/controls the frequency generated.....

The above circuit is simply an inverting amp stage (G = 1) followed by a V to I converter to drive / set the coil current.

How Does YIG Work? YIG is a ferrite material that resonates at microwave frequencies when immersed in a DC magnetic field. This resonance is directly proportional to the strength of the applied magnetic field and has very linear “tuning” over multi-octave microwave frequencies.

Regards, Dana.

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Hello Dana, what is the purpose of desgining a circuit at DC frequency using inductors?
It will be short circuit at DC.
Thanks.

Hello Dana, what is the purpose of desgining a circuit at DC frequency using inductors?
It will be short circuit at DC.
Thanks.
The coil is being driven by a DC current source. The coil sets up a field for the yig, see the doc
I attached in prior post. The freq of the YG is a f() of the field strength developed by the coil.

Regards, Dana.

Update:
Hello Dana,I thought so far there is only magnetic field in AC no DC in magnetic field.

So as you can see there are capacitors and opamps where the input is DC how sould i analze such circuit?
In analog design classes i am used to do small signal analysis of such a thing.
How can i analyse the performance of a DC input to and op-amp with capacitors ?
Thanks.

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Did your design classes cover integrator circuits, PI controllers and controlled current sources? The YIG driver is basically a voltage-to-current converter with PI characteristic. You can use small signal analysis to derive dynamic behaviour (bandwidth, feedback loop stability) and DC analysis for the V/I transfer function.

The cap used on the current source OpAmp you would consider infinite Z
for DC analysis, can be ignored. Also the R in series with it.

As a non YIG oscillator expert I read that to get it to osc requires, at minimum,
a DC static field. And that field strength determines osc freq. So if its varying then
you would experience FM modulation in YIG output freequency.

Regards, Dana,.

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