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Figure: OP amp filter circuit.

This is a problem from a book "Microelectronic circuits",7e by Sedra and smith, OUP.

The two op amp circuit is called an Antoniou Inductance circuit as it emulates an inductance and this circuit along with a capacitor and a resistor form a LCR circuit which is used for various applications. A difference is that the branch with capacitor, second from left has a resistance in place and the last branch with a resistor has a capacitance in place in the original circuit. I had obtained the resistor has 10 KΩ for an output sinusoidal signal of 1 kHz. When I tried to find the output voltage, it seemed that the voltage at \$V_2\$ is 0.7V looking at the diodes connected to \$V_2\$ and GND. Where is the output voltage taken? is it at \$V_2\$ or somewhere else? if its at \$V_2\$, it should be 0.7v Peak. How does one obtain the output voltage? A derivation is appreciated.

Problem:

Using C = 16nF, find the value of R such that the circuit in the figure produces 1 kHz sine wave. If the diode drop is 0.7V, find the peak-to-peak amplitude of output sine waves. (Hint: A square wave with peak-to-peak amplitude of V volts has a fundamental frequency component of \$\frac{4V}{π}\$ volts peak-to-peak amplitude)

Answers given: 10kΩ, 3.6V

Reference: Microelectronic circuits - Theory and applications, 7e, Sedra and smith, page 1082, OUP india.

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  • \$\begingroup\$ it seems that there is a bandpass filter in it which tunes to a certain frequency and therefore its a tuned oscillator? This depends on the values of R,L,C as they can be configured to make it a bandpass filter. \$\endgroup\$
    – Amit M
    Commented Sep 5 at 10:24

1 Answer 1

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The inductance simulator circuit appears to me to be a variant of Antoniu's original circuit, with C having been exchanged for R3. The two opposing diodes, as far as the signal is concerned, are a distorting non-linearity which produces harmonics. There is a possibility that oscillations may be triggered:

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    \$\begingroup\$ Where is the equation for peak to peak output voltage signal and what is its value? Can you please post your solution as text rather than as a image? It makes looking up your solution easier. Thanks very much! \$\endgroup\$
    – Amit M
    Commented Sep 5 at 16:11
  • \$\begingroup\$ It's dinner time here, so I'll get back to you tomorrow. \$\endgroup\$
    – Franc
    Commented Sep 5 at 17:11

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