# apd frequency response

Discussion in 'Electronic Design' started by [email protected], Aug 22, 2007.

1. ### Guest

I got a task from my professor to explore pulse response of APD.
The APD is Hammamatsu APD module C5331 and it has bandpass frequency
response
(4 kHz~ 100 MHz)
To find the response of the detector to given pulse
signal(square ) ,I think that I need to know
exact frequency response formula of the APD module.

I don't know the origin of bandpass response exactly.
Is it from some internal filter circuitry?
Or..does it have another origin?

If it's from bandpass filter inside the module, it will be possible
to
apply the formulas from electronics .

2. ### Rene TschaggelarGuest

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

3. ### Guest

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.

DSP and Mixed Signal Consultant
www.abvolt.com

5. ### John LarkinGuest

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

John

6. ### LVMarcGuest

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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