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I'm trying to build a sine wave generator following this walkthrough. Specifically, I'm attempting the Clapp circuit as I'm targeting about 113 kHz.

Here is the circuit schematic:

schematic

In the article the author mentions these formulas for calculating the frequency:

$$f=\frac{1}{2\pi\sqrt{LC}}\\ C=\frac{1}{\frac{1}{C_5}+\frac{1}{C_2}+\frac{1}{C_4}}$$

My question is this: Do I need to convert μH to H and pF to F in order to calculate the correct frequency? I created an Excel spreadsheet and set 1 μH equal to 10-6 H and 1 pF equal to 10-12 F. Using those values I calculated L1 to be 220 μH, C5 to be14000 pF, and C2 and C4 both to be 50000 pF for a frequency of 113.27 kHz.

I know that I'll need to adjust the capacitor values based on what is available, but I'm just trying to make sure that my calculations are correct before I build the circuit and order parts.

ocrdu
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Sean
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    One thing you could try for confirmation is simulating the circuit in a robust simulator, something like LTspice. In the simulator, you can then connect a load resistance and see how it affects the oscillator; with C3 being just 10nF, it will have a fairly high output impedance. Might consider an op-amp follower for it's very high input and low output impedance (less interfering with source signal and easier to interface to any load.) – rdtsc Nov 01 '22 at 20:01
  • Use a simulator. It's a modern craze that is catching on; don't miss the boat; you definitely won't regret it although the learning curve can hurt (but worth the effort on every circuit you'll ever design from now on). – Andy aka Nov 01 '22 at 20:22

1 Answers1

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Here is just an example with real parts for the 110 kHz Clapp oscillator. For a higher quality factor (Q), choose a higher value of L1. Of course, this also depends on how much bandwidth we will need (e.g. for modulation).

enter image description here

For such a low frequency, a Wien bridge oscillator with a suitable operational amplifier would perhaps be simpler.

csabahu
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