CXA1992BR
APC & Laser Power Control
VCC
C2
100µ
R1
22
LD
36
37
R6
1k
VCC
LDON
L1
10µH
R10
56k
130mV
PD
R8
10k
R3
100
C1
1µ
R2
500
LD PD
R5
55k
R12
56k
R11
10k
R4
10k
VREF
VEE
GND
VL
VEE
VEE
LPC ON/OFF
50%/17%
R14
12.5k
RF_I
1.1Vpp
32
33
C3
0.01µ
3V: 1.2V R7
5V: 1.52V 13k
670mV
RF_O
R9
41k
VC
RF
VEE
35
R13
1M
C4
1µ
VEE VEE
• APC
When the laser diode is driven by a constant current, the optical power output has extremely large negative
temperature characteristics.
The APC circuit is used to maintain the optical power output at a constant level.
The laser diode current is controlled according to the monitor photo diode output.
• Laser power control
The RF level is stabilized by attaching an offset to the APC VL and controlling the laser power in sync with the
RF level fluctuations.
The RF_O and RF_I levels are compared and the larger of the two is smoothed by the RFTC's external CR.
This signal is then compared with the reference level.
The laser power is controlled by attaching an offset to VL according to the results of comparison with the
reference level.
Set the reference level to 670mV. (center voltage reference)
LPC ON/OFF and LD ON/OFF control is performed with commands.
The laser power control limit can also be switched between ±50% and ±17% with commands.
LPC
OFF
ON
LPCL
—
VL variable range
Approximately 1.27V
Approximately 1.27V ± 625mV
Approximately 1.27V ± 208mV
– 21 –
±50%
±17%
ON
SONY [ SONY CORPORATION ]
