ds1861 Maxim Integrated Products, Inc., ds1861 Datasheet - Page 14

• Manufacturer Part Number: ds1861
• Description: Ds1861 Full Laser Control With Fault Management
• Manufacturer: Maxim Integrated Products, Inc.

Full Laser Control with Fault Management
Figure 9. BMD Disturbance Current
Figure 10. Laser Diode Bias Current Definitions
14
____________________________________________________________________
I
TH
I
0
P0
CURRENT (mA)
I
1
AVERAGE
I
APC
POWER
f
ERU
I
TIME
1
MOD
I
DIST
2
I
MOD
I
MOD
2
P1
P
MOD
Once the extinction ratio is expressed as a function of
the average power and the modulation power, the
equation can then be written in terms of the modulation
and average power currents. The modulation current
(I
I
(I
referenced to the threshold current (I
1
can now be rewritten as the following equations.
The APC loop is already controlling I
average power at a constant value, so the DS1861 out-
puts I
control the extinction ratio. The DS1861 determines the
I
where N is a variable gain that can be used to adjust
the extinction ratio.
Substituting into the previous extinction ratio equation
yields the extinction ratio as a function of N.
0
MOD
/
MOD
APC
2
currents (I
I
Extinction Ratio
Extinction Ratio
0
) is the arithmetic mean of the I
/I
) is defined as the difference between the I
- I
MODSET
APC
TH
). After defining these currents, the equation
ratio according to the following formula,
MOD
so that I
I
I
MOD
= I
APC
=
=
1
I
1
I
1
APC
APC
- I
+
−
MOD
=
0
2
2
1
1
). The average power current
×
+
×
−
30
N
1
2
1
2
/I
30
30
N
N
APC
I
I
MOD
MOD
x
×
×
A
A
A
A
A
A
remains constant to
M
D
M
D
M
D
=
1
1
1
=
APC
+
−
and I
60
APC
60
2
2
1
1
×
×
+
−
to keep the
N
N
I
I
I
I
MOD
MOD
=
APC
0
APC
A
A
A
A
currents
1
M
D
M
D
/
2
1
I
and
1
+