apd frequency response

Usually the roll off at higher frequencies is due to the diode capacitance which is proportional to the area of the diode. Therefore the faster diodes have less area.

Rene

The frequency response of the APD module is determined by the capacitance of the APD itself and the gain/phase response of the transimpedance amplifier cascade connected to the APD. Generally, the overall response is a lowpass function of the 2nd order.

Vladimir Vassilevsky DSP and Mixed Signal Consultant

As mentioned, it's a combination of the diode capacitance and amplifier response, if any.

Either get Hammamatsu to supply the data, or measure it experimentally. A cheap laser diode, like a Lasermate VCSEL, driven by a good pulse generator, can generate a pretty clean light step or impulse with 100 ps risetime. A sub-ns impulse would be ideal for characterizing your gadget.

John

Professors are funny that way :0)

first cut analysis is as follows:

treat the system as a first order low pas filter with a 100 MC upper cut-off.

Then the response to a step is the derivative of impulse response of the filter function, itself.

therefore the out put to a step will be a rise time limited signal ,, the rise time will be about 3.42 nS in this case. you will have to derive this or produce the bw and rise time relation ship.

the low frequency of 4 KC means that if you have a single step from "no light" to "light" then you get this 3.42 nS rise tie limited signal.. the 4 kc low frequency mans, the system is "AC coupled" and the step output will begin to droop relitve to the 4.2 mS time frame. normally for the interesting light signals are pulsed signal 10 - 500 nS wide so the droop you get with a 4 KC low frequency cut -in is minimal.

Best regards and happy designing

marc

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