Models 2051 & 2053
General Features & Principles • 9
General Features & Principles
Photoreceiver Circuitry
The circuitry inside the Model 205X consists of a
photodiode followed by a three-stage transimpedance
amplifier. The gain can be adjusted from 626 V/A to
18.8x10
6
V/A in 5-dB steps. The low-noise amplifier
design is optimized to maximize bandwidth at each
gain setting. At the higher gain settings, the bandwidth
is limited by amplifier gain-bandwidth product. The
plots of Figure 3 show the typical frequency responses
for the different gain settings.
Figure 2:
Functional
schematic of
the Model 205X
circuitry
+15 V
-15 V
GND
BATT
9 V
INDEPENDENTLY
ADJUSTABLE 6-dB/OCTAVE
HIGH- AND LOW-PASS FILTERS
+9 V
DETECTOR
HOUSING IS
GROUNDED
SMA
ADJUSTABLE-GAIN
STAGE
x3
x1
ADJUSTABLE-GAIN
STAGE
x10
4
x10
3
x10
2
x10
x1
f_L
f_H
BATT
9 V
+9 V REG
-9 V REG
+9 V
-9 V
205x 10MHz Adj Rcvr revA.fm Page 9 Monday, January 10, 2005 9:29 AM
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