Can anyone help me analyze the opamp based oscillator

Discussion in 'General Electronics Chat' started by Dingli, Nov 6, 2014.

  1. Dingli

    Thread Starter New Member

    Nov 6, 2014
    Hi, I'm studying the opamp based oscillator which is used in a proximity switch. I find an LC oscillator which has an LC tank and an inverting amplifier. I don't how the positive feedback happens since LC tank is only connected to the non-inverting input of the opamp. Can anyone help me analyze this circuit and explain the operation? In addition, I have built this circuit in MULTISIM to do simulation. The opamp I used is TL083 which is a general purpose opamp. When I run the simulation, I found the circuit does oscillates, the frequency is LC resonant freq, but the opamp saturates, the output is like a square wave. No matter how I changed the resistors, the circuit never outputs a sine wave, how can this problem be solved? Thanks very much!!
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    The output being connected to the tank and to the non-inverting input IS the positive feedback. Try moving the 20k resistor (R2) so it is between the + input and the tank. The tank is inputting directly into the op-amp in the current configuration.