For an assignment I have to create a sinusoidal oscillator with 5 Vpp (centered around 0 V) oscillating at 10.0 kHz. The oscillator works as expected, at the right frequency, but the voltage needs to be regulated between 0 to 5 Vpp.

The following picture shows my design so far; Wien-bridge oscillator with low pass filter As you can see the circuits consists of the Wien-bridge oscillator with a low-pass filter to attenuate the higher harmonics. I have tried using a voltage divider but that method does not hold for 0 to 5 Vpp. I am only allowed to use basic components, like the 741 opamp and 1N149 diodes, besides capacitors and resistors.

Does anyone know a method on how to achieve 0 to 5 Vpp regulation using these simple components?

  • 2
    \$\begingroup\$ It is unclear what needs to determine the amplitude. If it is simply "turning a knob" then I would add a potmeter at the signal output, similar to how an audio volume control works. If you need to control the signal amplitude from an external (DC) voltage then I do not see a solution with the allowed components. \$\endgroup\$ – Bimpelrekkie Jan 15 '19 at 9:50
  • \$\begingroup\$ Are you allowed to use a second opamp (as an inverting amplifier)? \$\endgroup\$ – LvW Jan 15 '19 at 10:18
  • \$\begingroup\$ @Bimpelrekkie That does make sense, but then I cant change my input voltage anymore, from 15 volts to say 20. \$\endgroup\$ – Marinus Leeuwerik Jan 15 '19 at 11:35
  • \$\begingroup\$ @LvW yes I am, as long as it does not add any substantial disturbance it should be okay. \$\endgroup\$ – Marinus Leeuwerik Jan 15 '19 at 11:35
  • \$\begingroup\$ ...but then I cant change my input voltage anymore, from 15 volts to say 20 You mean supply voltage instead of input voltage I guess. You can still change the supply voltage but the output voltage will then change as well. If that's not allowed then do not use voltage dividers (R5, R6, R7, R8) for amplitude limitation but replace R5 and R7 with a stack of diodes for example to get a more stable voltage. \$\endgroup\$ – Bimpelrekkie Jan 15 '19 at 11:54

So, based on the comments, the voltage control was actually quite straightforward. Using a classic inverted amplifier. Where R11 is fixed based on input voltage, and R10 a potentiometer controlling the output voltage between 0 - 10 Volts which is halved by the second-order Butterworth filter.

enter image description here

Thank you for the help everyone!


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