Nanosecond Photodetectors
General Features and Principles • 11
General Features and Principles
Photoreceiver Circuitry
The circuitry inside the Model 162X consists of a
reverse-biased photodetector and a load resistor with
three settings:
50
Ω
,
10 k
Ω
, and
Open
. The 50-
Ω
set-
ting has 50-V/A sensitivity and can be used to achieve
the
≤
1-nanosecond response time. The 10-k
Ω
setting
has a reduced time response but gives a higher sensi-
tivity (10,000 V/A) and can be used for alignment pur-
poses and for detecting low-power pulses. The
Open
setting allows you to hook-up your own external load
resistor and choose the best gain-bandwidth combina-
tion for your application.
Figure 3:
Functional
schematic of
the Model 162X
circuitry
Frequency and Time Response
The nanosecond photodetector circuitry is quite
straightforward, consisting only of the photodiode,
battery bias and a selectable load resistor. The speed
limitation of the circuit is established by the junction
Output
Open
10 k
Ω
50
Ω
ON
+V
LED
Battery Check
Circuit
OFF
Batt
Chk
162x nanosec revB.fm Page 11 Friday, August 17, 2001 5:51 PM
