The series resitance of a photodiode in not as important as the shunt resistance ..
It is common industrial practice to put a 10mV reverse bias on the photodiode and measure current ..
The ratio between the bias voltage and current determine the shunt resistance value ..
Regards,
IanP
What will you use this photodiode ?? RF Transmission or simple ON/OFF or low frequency switching..??
The series resistance of a diode (also a photodiode) can be understood as a deviation from ideal diode behaviour, that mainly shows at higher currents. You can derive it from the measured current/voltage characteristic. Of course you should keep maximum ratings for the measurement, and you would want to aplly pulse measurements at higher currents to avoid a faulty measurement due to temperature dependant diode forward voltage. A diode charateristic measurement would rather use (pulsed) constant current than voltage.
It's most likely easier to refer to manufacturer data, if available. You should also consider, that a lumped series resistance + ideal diode + capcitance equivalent circuit is a simplification, that won't be able to model the high frequency behaviour of a photodiode very well.
Hi E Kafeman,
Thanks for the info but I am rahter interested in measuring the series resistance. The operation of a photodiode is no problem, I am trying to determine this resistance an preferably at voltages of typical diode operation, namely at reverse bias. Any idea?
Thanks
---------- Post added at 10:04 ---------- Previous post was at 10:02 ----------
Hi FvM
Thanks for the detailed and very useful info! Is there anyway that I can measure the series resistance at voltages of normal operation (reverse bias). Or at least near zero bias? Any idea/suggestion would be grately appreciated!
Thanks, regards
I agree with the commentors. Your thread title is right, but your method is wrong. Since the diode is reverse biased during normal operation, measuring the "series resitance" would be meaningless.
You really want to measure the thevenin equivalent, which is the effective parallel resistance when it is reverse biased.
You couldn't clarify yet, if the observed differences in diode I-V characteristics are actually related to a diode series resistance. In a first order, you have an exponential diode characteristic. According to the diode area and other parameters (e.g. semiconductor doping) you'll observe different saturation currents in the basic diode characteristic. As already said, the ideal diode characteristic will be modified by a series resistance, which can be imagined as resistance of the diode contacts. But depending on the utilized diode current range, you won't necessarily see the series resistance.
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