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LC Tank circuit with comparator frequency error

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sonar_abhi

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Hello All,

I am designing a basic LC Tank circuit with comparator to be used in an inductance measurement circuit.

Ideally, when the circuit is charged for a couple of seconds and then the switch disconnected, the circuit frequency should be 13.30kHz according to the resonant frequency formula but when I simulated the circuit, the frequency measured is 203Hz.

Can anybody please check if the circuit is correct or not?

Screenshot.jpg
 

Hi,

Show the scope picture of the voltage at the C.

I assume it's distorted by the comparator input.

Klaus
 

sonar_abhi said:
Hello All,

I am designing a basic LC Tank circuit with comparator to be used in an inductance measurement circuit.

Ideally, when the circuit is charged for a couple of seconds and then the switch disconnected, the circuit frequency should be 13.30kHz according to the resonant frequency formula but when I simulated the circuit, the frequency measured is 203Hz.

Can anybody please check if the circuit is correct or not?

View attachment 140417
Click to expand...

Are you expecting this circuit will oscillate during a limited period after a small charging ( or driven by an impulse ) ???
 

As the LC tank rings, the capacitor goes into the negative region for part of each cycle. Negative-polarity input voltage is not compatible with an op amp running from a single positive supply.
 

@ BigBoss, I have checked the circuit simulation in Proteus8. The circuit is working, i.e., when the switch is closed and then opened after a brief period, say for a couple of seconds, I am getting a decaying square wave at the output as expected but the frequency is way low, 203 Hz. According to the calculation of resonant frequency it should be around 13KHz.

@KlausST, I will post the scope screenshot in a couple of hours.
 

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