Zener diode

[Vinit_dhulla]

Hello,
I am working on the design of a 10MHz active quenching circuit for avalanche photo diode.
I would like to know what is the max speed at which a zener diode can operate, is there any zener diode available which can operate around or above 10MHz.
Any suggestions would be appreciated.

Regards,
Vinit.

 

[Optikon]

Hello,
I am working on the design of a 10MHz active quenching circuit for avalanche photo diode.
I would like to know what is the max speed at which a zener diode can operate, is there any zener diode available which can operate around or above 10MHz.
Any suggestions would be appreciated.

Regards,
Vinit.

Well, I believe that the speed at which you can operate will be (in part)determined by the junction capacitance of the zener. This capacitance is a function of voltage (might find a curve on a datasheet). This capacitance works with circuit impedances to slow the breakdown on the zener.

The larger the junction C, the more high speed current it will shunt across the zener (making that current not available for breakdown effect)

Here is what I would suggest for maximum speed of operating the zener (maximum here means best chance but not necessarily good enough for your application):

1) Bias the zener with a such a voltage(or constant current) that the zener operating point is just below the knee. This will reduce junction capacitance.

2) Drive the zener into breakdown with your 10MHz source. You can do this with a voltage or current.

Since you did not mention your source, some things to consider..

If you use a voltage source, make sure it is low impedance out to at least 50 MHz.. (in otherwords, if you use an op amp or the like, buffer the output with a high speed complimentary stage for example) Most opamp outputs are something like 100's or K Ohms out at 10MHz.

You may have a function generator that is good enough but test the output impedance at 10MHz first to make sure it will work ok.

If you use a current source, keep the current as high as possible so that it can charge up circuit parasitics quickly.