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?

 

Hi,

Show the scope picture of the voltage at the C.

I assume it's distorted by the comparator input.

Klaus
 


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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