HDSP-420X Agilent(Hewlett-Packard), HDSP-420X Datasheet - Page 4

• Manufacturer Part Number: HDSP-420X
• Description: 20 mm (0.8 inch) Seven Segment Displays
• Manufacturer: Agilent(Hewlett-Packard)

Figure 3. Laser Driver Block Diagram and External Circuitry.
described in more detail in the
laser driver operation section
below.
Transmitter Laser Driver
Operation
The block diagram of the HDMP-
1512, Tx, laser driver circuitry is
shown in Figure 3. The laser
driver is enabled by setting
-LZON (pin 30) low and
LZPWRON (pin 36) high. The
circuitry in Figure 3, shown
outside the chip boundary (dotted
box), illustrates the external
components required to complete
a typical laser driver connection.
The input data source to the laser
driver is user selected from either
the internally generated data
stream, or an externally supplied
high speed data stream. The
externally supplied data stream is
applied to the high speed input
LZPWRON
V
GND_LZ
V
CC
FAULT
CC
-LZON
_LZ1
± SI
_LZ
11
12
16
23
24
25
26
30
36
29
INTERNAL
STREAM
DATA
DETECTOR
LASER ON
V
SELECT
ERROR
INPUT
CC
MUX
-LZBG
15
27
LZTC
0.1 µF
REFERENCE
between these two data sources
through the proper settings of
pins TS1, TS2, and EWRAP (pins
76, 75, and 71). The possible
combinations of active inputs and
outputs are shown in the Input/
Output Select Table. The chosen
high speed input is then modu-
lated onto the laser by the ac
amplifier. The external poten-
tiometer, Pot 2, shown connected
to pin LZCSE (# 14) is used to
adjust the laser modulation
depth. The laser driver output is
at pins 19 and 20,
Laser diode dc bias control is
provided through the LZDC
(# 21) pin. Adjustment of Pot 1
sets the nominal dc bias desired
for the laser diode. The
equivalent output circuit of LZDC
is shown in Figure 4. Laser diode
fault and safety control is imple-
mented through the combination
DETECTOR
DETECTOR
BANDGAP
BANDGAP
DISABLE
WINDOW
AC AMP
SI pins. The user selects
LZBTP
Tx CHIP BOUNDARY
POT 1 5 K
28
22
AC AMP
+
–
–
+
DC
OP-AMP
LZMDF
LZOUT.
LZDC
10 nF
10 nF
17
19
20
14
21
V
+LZOUT
CC
-LZOUT
LZCSE
0.1 µF
_LZAC
POT 2
50
5
0.1 µF
0.1 µF
Figure 4. LZDC Equivalent Output
Circuit (Tx pin # 21).
of the window detector, error
detector, Laser On pin # 30
(-LZON), laser monitor diode
feedback pin # 22 (LZMDF), and
the op-amp dc bias control
circuit. The window detector
monitors the voltage on pin
LZMDF. If this voltage goes out
of range by more than
from the nominal setting, the
25
5
25
TRANSMISSION LINE
P1 ( >= 100)
0.1 µF
V
8
CC
_LZ
301
25
0.1 µF
54
V
CC
400
0.1 µF
V
P2
CC
2.2
EXTERNAL
CONTROL
10%
659
LZDC