The 1n4001 seems to follow the? ?Cj = K/sqrt(V)? ?formula rather closely.
From the graph of fig 4 on page 2 of the 1n4001 datasheet at? ?
? ??
I read the following sample of values:??1v:30pf? 9v:10pf? 30v:5pf? 80v:3pf
Using the midrange 9v:30pf pair to compute? ?K = 10*sqrt(9) = 30,
we get the following results from Cj = K/sqrt(V) = 30/sqrt(V):
? ? 1v: 30.0pf? ? 9v 10.0pf? ? 30v: 5.48pf? ?80v: 3.35pf
The figures computed from? Cj=K/sqrt(V)? follow the graph quite well.
Some diodes don't follow our formula so closely.
Take a look at the figure on the left side of page 2 for the 1SV322:
? ??
Using that figure, I read:? ? 6v:5pf 4.5v:6pf 2.8v:10pf 1.6v:20pf? 0.5v:38pf
Using the 2.8v:10pf center value pair, I find that K=16.73? and Cj=K/sqrt(V) gives:
? ?6v: 6.83pf? ? 4.5v: 7.88pf? ? 2.8v: 10.0pf? ? 1.6v 13.23pf? ? 0.5v: 23.66pf
Note that values from the figure have higher capacitance at low voltages than our computed values.
So this specially designed 1SV322 varactor diode is even more non-linear than the 1n4001.
Do I have something wrong here?
Why would we not use a 1n4001 instead?
Perhaps performance at high frequencies, where the 1n4001 might show a bit of PIN behavior?
Curious.
Jerry, KE7ER
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