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C30921S 参数 Datasheet PDF下载

C30921S图片预览
型号: C30921S
PDF下载: 下载PDF文件 查看货源
内容描述: 硅雪崩光电二极管 [Silicon Avalanche Photodiodes]
分类和应用: 光电二极管光电二极管
文件页数/大小: 7 页 / 234 K
品牌: PERKINELMER [ PERKINELMER OPTOELECTRONICS ]
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Appendix  
Operation of the C30902S and C30921S  
in the Geiger Mode  
Passive-Quenching Circuit  
The simplest, and in many cases a perfectly adequate method  
of quenching a breakdown pulse, is through the use of a  
current limiting load resistor. An example of such a "passive"  
quenching circuit is shown in Figure 9. The load-line of the  
circuit is shown in Figure 10. To be in the conducting state at  
Introduction  
When biased above the breakdown voltage, an avalanche  
photodiode will normally conduct a large current. However,  
if the current is such that the current is limited to less than  
a particular value (about 50 µA for these diodes), the  
current is unstable and can switch off by itself. The  
explanation of this behavior is that the number of carriers in  
the avalanche region at any one time is small and  
fluctuating wildly. If the number happens to fluctuate to  
zero, the current must stop. It subsequently remains off  
until the avalanche pulse is retriggered by a bulk- or photo-  
generated carrier.  
V
two conditions must be met:  
BR  
1. The avalanche must have been triggered by either a  
photoelectron or a bulk-generated electron entering the  
avalanche region of the diode. (Note: holes are inefficient at  
starting avalanches in silicon.) The probability of an avalanche  
being initiated is discussed above.  
2. To continue to be in the conducting state a sufficiently large  
current, called the latching current I  
, must be passing  
LATCH  
through the device so that there is always an electron or hole in  
The C30902S and C30921S are selected to have small  
bulk-generated dark-current. This makes them suitable for  
the avalanche region. Typically in the C30902S and C30921S,  
I
I
=50 µA. For currents (V -V )/R , much greater than  
BR  
LATCH  
B
L
low-noise operation below V  
or of photon-counting  
BR  
in the Geiger mode. In this so-called Geiger  
, the diode remains conducting. If the current (V -  
LATCH  
R
above V  
BR  
V
)/R , is much less than I  
BR  
, the diode switches almost  
LATCH  
L
mode, a single photoelectron (or thermally-generated  
immediately to the non-conducting state. If (V -V )/R , is  
BR  
B
L
electron) may trigger an avalanche pulse which discharges  
approximately equal to I  
, then the diode will switch at an  
LATCH  
the photodiode from its reverse voltage V to a voltage  
R
arbitrary time from the conducting to the non-conducting state  
depending on when the number of electrons and holes in the  
avalanche region statistically fluctuates to zero.  
slightly below V . The probability of this avalanche  
BR  
occurring is shown in Figure 8 as the "Photoelectron  
Detection Probability" and as can be seen, it increases with  
reverse voltage V . For a given value of V -V , the  
When R is large, the photodiode is normally nonconducting,  
L
R
R BR  
Photoelectron Detection Probability is independent of  
temperature. To determine the Photon Detection  
and the operating point is at V - I R in the non-conducting  
R
ds L  
state. Following an avalanche breakdown, the device recharges  
to the voltage V - I R with the time constant CR where C  
Probability, it is necessary to multiply the Photoelectron  
Detection Probability by the Quantum Efficiency, which is  
shown in Figure 2, the Quantum Efficiency also is relatively  
independent of temperature, except near the 100 nm cutoff.  
R
ds L  
L
is the total device capacitance including stray capacitance.  
Using C = 1.6 pF and R = 200.2 Ka recharge time constant  
L
of 0.32 microseconds is calculated, in reasonable agreement  
with observation as shown in Figure 9. As is also evident from  
The C30902S and C30921S can be used in the Geiger  
mode using either "passive" or "active" pulse quenching  
circuits. The advantages and disadvantages of each are  
discussed below.  
Figure 9, the rise-time is fast, 5 to 50 ns, decreases as V -  
R
V
increases, and is very dependent on the capacitances of  
BR  
the load resistors, leads, etc. The jitter at the half-voltage point  
is typically the same order of magnitude as the rise-time. For  
timing purposes where it is important to have minimum jitter,  
the lowest possible threshold of the rising pulse should be  
used.