Eg. Fundamental is 5 MHz & you get harmonics at 10 MHz, 20MHz, etc.
How is the diode’s non-linearity causing this? I can’t find a way to visualize it.
In: 10
Check out these graphs.
The first one shows the output of a diode subjected to a sinusoidal input. As you can see, the bottom half of the sine wave is cut off by the action of the diode.
https://www.wolframalpha.com/input?i=plot%28max%28sin%282+pi+t%29%2C0%29%29+with+0%3Ct%3C2
The next one shows the [best possible representation](https://en.wikipedia.org/wiki/Trigonometric_series) of the diode’s signal, using a constant output plus an oscillating output at the *same frequency* as the input.
https://www.wolframalpha.com/input?i=plot%28max%28sin%282+pi+t%29%2C0%29%2C1%2Fpi+%2B+%281%2F2%29+sin%282+pi+t%29%29+with+0%3Ct%3C2
You can see that because the clipped sine wave generated by the diode isn’t a pure sine wave, this isn’t a perfect representation. Over the course of one cycle, the “best representation” is too high, too low, too high, too low: it’s off by an amount that cycles twice for every cycle of the input wave.
Which is to say that we can get an even better representation of the diode’s output by **adding some signal with twice the frequency of the input:**
https://www.wolframalpha.com/input?i=plot%28max%28sin%282+pi+t%29%2C0%29%2C1%2Fpi+%2B+%281%2F2%29+sin%282+pi+t%29%2C+1%2Fpi+%2B+%281%2F2%29+sin%282+pi+t%29+-+%282%2F%283+pi%29%29+cos%284+pi+t%29%29+with+0%3Ct%3C2
… which is better, but still not perfect: it’s too high, too low, 4 times per repetition of the diode’s output signal. So we can fix it by **adding some signal with *four times* the frequency of the input:**
https://www.wolframalpha.com/input?i=plot%28max%28sin%282+pi+t%29%2C0%29%2C1%2Fpi+%2B+%281%2F2%29+sin%282+pi+t%29%2C+1%2Fpi+%2B+%281%2F2%29+sin%282+pi+t%29+-+%282%2F%283+pi%29%29+cos%284+pi+t%29+-+%282%2F%2815+pi%29%29+cos%288+pi+t%29%29+with+0%3Ct%3C2
… and so on. The diode output can be represented as — no, the diode output *is* — a signal composed of the base frequency, plus twice the base frequency, four times that, and so on.
Latest Answers