A guard circuit prevents stray or surface leakage
from being measured by the current meter.
In this analysis, the effects of shot noise, surface leakage current and thermal noise current associated with APD receiver are considered.
Where the exponent x varies between 0 and 1.0 depending on the APD material and structure, M the average APD gain, [R.sub.0] the unity gain responsivity, e an electron charge, [I.sub.BD] the average bulk dark current, which is multiplied by the avalanche gain, [I.sub.SL] the average surface leakage current, which is not affected by avalanche gain, [B.sub.e] the receiver electrical bandwidth, [K.sub.B] the Boltzmann's constant, T the receiver noise temperature, and [R.sub.L] the receiver load resistor.
Guard system eliminates the effect of surface leakage
current on high-resistance measurements.
The current of surface leakage is determined by a certain equivalent leakage resistance [R.sub.12] Consequently, the total current through the collector junction can be written as
The surface leakage is expressed by the shunt resistance l2 R and it has significant influence on Si based solutions, but much weaker influence on structures based on other materials.
It is useful when surface leakage
may be a problem, but, since it is not exact, it should be used with wide margin of safety.
The shunt resistance represents the loss due to surface leakage
along the edge of the cell or to crystal defects.
was found to be patchy, a result similar to that observed in other controlled release facilities internationally.
C: 1000 M.Ohms/Km, Minimum Surface Leakage
Resistance- 90 M.Ohms, Ac Test Voltage- 5400V/1 Min.