Schematic picture

I have a waveform selector circuit shown above. The input signal is a 1 kHz alternating Square wave with a pk-pk value of 8.5V (above the x-axis).
The output waveforms in order starting from the left is a square wave, sawtooth wave, triangle wave and sine wave.

I want to calculate the theoretical voltage value of the sine wave (fourth switch from the left). I tried writing KVL equations but the circuit has a feedback capacitor on the collector terminal of the transistor. How do I calculate the output voltage?

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  • \$\begingroup\$ I have edited the question so the image is hosted on SE. However, this needs a review vote. \$\endgroup\$ – apnorton Apr 30 '13 at 14:36
  • \$\begingroup\$ thank you! i can't upload images because i need +10 reputation \$\endgroup\$ – anandan111 Apr 30 '13 at 15:48

What you have is a succession of low pass RC filters operating on a square wave followed by an active filter. As each filter takes effect, the waveform becomes rounder since its high frequency components are being reduced in magnitude. Calculating the value of the sine wave voltage, which includes the effects of all of the filters, is a difficult paper calculation because the filters interact. Since R4, R5, and R6 are the same value, each RC stage affects the one preceding it. Your best bet is to use a circuit analysis program.


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