A varactor diode is not used at 0V so it is not on the datasheet. Whoever told you the capacitance is 40pF at 0V then ask them.
Maybe at 0V then the signal strength changes the capacitance too much and it is useless for tuning.

can you see this page

 

Hallo,

The shown PDF is not from the manufacturer.
In the application note from Zetex the voltage is 0.1 Volts minimum:



Bertus

 

Hallo,

The shown PDF is not from the manufacturer.
In the application note from Zetex the voltage is 0.1 Volts minimum:

View attachment 146708

Bertus

so the maxium is 6.5pf RIGHT?

 

Hello,

Wich varicap do you have?
A zetix ZC832 has a maximum capacitance of about 40 pF.

Bertus

 

Hallo,

The shown PDF is not from the manufacturer.
In the application note from Zetex the voltage is 0.1 Volts minimum:

View attachment 146708

Bertus

thank you very much, i wil like to ask you this one
If you are going to divide anything, you can pick any number between the minimum capacitance ratio of 5.0 and the maximum capacitance ratio of 6.5 and divide that capacitance ratio number into any value between the minimum and maximum capacitance values that occur with 2 V reverse bias and 20V reverse biased This range of values represents the maximum varactor capacitance. The result after dividing by the capacitance ratio will be the minimum varactor capacitance
for example 6.5pf /2V maximum capacitance and 6.5pf/20V minimum capacitance is like this?.

 

Hello,

When you look at the graph posted in post#42, the ZC832 has a value of about 4 pF @ 20 volts and about 40 pF @ 0.1 Volts.
The ratio for this range will be 40/4 is 10.

Bertus

 

Hello,

When you look at the graph posted in post#42, the ZC832 has a value of about 4 pF @ 20 volts and about 40 pF @ 0.1 Volts.
The ratio for this range will be 40/4 is 10.

Bertus

here says that the ratio is 5 and 6.5, Wich is true?

 

Hello,

Both can be thrue.
It is a matter of scatter in the specs.
The diodes will have differences in production.

Bertus

 

The graph shows a capacitance of 40pF at 0.1V but shows a capacitance of only 21pF at 2V.
The chart shows the low ratio down to 2V, not the high ratio down to 0.1V.

 

Hello,

Both can be thrue.
It is a matter of scatter in the specs.
The diodes will have differences in production.

Bertus

THANK YOU VER MUCH, NOW I UNDERSTAND ;-------))))))))))))

 

The graph shows a capacitance of 40pF at 0.1V but shows a capacitance of only 21pF at 2V.
The chart shows the low ratio down to 2V, not the high ratio down to 0.1V.

THANK YOU AUDIOGURU, NOW I KNOW.;-)