參數(shù)資料
型號(hào)： TZA3001BHL
廠商： NXP SEMICONDUCTORS
元件分類： 其它接口
英文描述： SDH/SONET STM4/OC12 laser drivers
中文描述： SPECIALTY INTERFACE CIRCUIT, PQFP32
封裝： 5 X 5 X 1.40 MM, PLASTIC, LQFP-32
文件頁(yè)數(shù)： 7/22頁(yè)
文件大小： 517K
代理商： TZA3001BHL
1999 Aug 24
7
Philips Semiconductors
Preliminary specification
SDH/SONET STM4/OC12 laser drivers
TZA3001AHL; TZA3001BHL;
TZA3001U
DC reference currents are applied to pins ZERO and ONE
to set the MPD reference levels for laser LOW and laser
HIGH.Aresistorconnectedbetweenpin ZEROandV
CC(R)
and a resistor connected between pin ONE and V
CC(R)
is
sufficient, but current DACs can also be used.
The voltages on pins ZERO and ONE are held constant at
a level of 1.5 V below V
CC(R)
. The reference current
applied to pin ZERO is multiplied by 4 and the reference
current flowing into pin ONE is multiplied internally by 16.
The reference current and the resistor for the optical ONE
regulation loop (modulation current control) can be
calculated using the following formulae:
16
(1)
(2)
The reference current and resistor for the optical ZERO
regulation loop (bias current control) can be calculated
using the following formulae:
1
4
(3)
(4)
In these formulae, I
MPD(ONE)
and I
MPD(ZERO)
represent the
monitor photodiode current during an optical ONE and an
optical ZERO, respectively.
Example:
A laser is operating at optical output power
levels of 0.3 mW for laser HIGH and 0.03 mW for laser
LOW (extinction ratio of 10 dB). Suppose the
corresponding MPD currents for this type of laser are
260 and 30
μ
A, respectively.
In this example the reference current is
16
and flows into pin ONE.
This current can be set using a current source or simply by
a resistor of the appropriate value connected between
pin ONE and V
CC(R)
. In this example the resistor would be
16.25
The reference current at pin ZERO in this example is
1
4
7.5
and can be set using a resistor
I
ONE
1
I
MPD (ONE)
×
=
A
[ ]
R
ONE
ONE
I
MPD (ONE)
I
=
=
[
]
I
ZERO
I
MPD (ZERO)
×
=
A
[ ]
R
ZERO
ZERO
I
MPD (ZERO)
I
=
=
[
]
I
ONE
1
260
×
16.25
μ
A
=
=
R
ONE
--1.5
92.3 k
=
=
I
ZERO
30
×
7.5
μ
A
=
=
R
ZERO
1.5
200 k
=
=
It should be noted that the MPD current is stabilized, rather
than the actual laser optical output power. Deviations
between optical output power and MPD current, known as
‘tracking errors’, cannot be corrected.
Designing the modulation and bias loop
The optical ONE and ZERO regulation loop time constants
are determined by on-chip capacitances. If the resulting
time constants are found to be too small in a specific
application, they can be increased by connecting external
capacitors to pins TZERO and TONE, respectively.
The optical ONE loop time constant and bandwidth can be
estimated using the following formulae:
(5)
(6)
The optical ZERO loop time constant and bandwidth can
be estimated using the following formulae:
(7)
(8)
The term
η
LASER
(dimensionless) in the above formulae is
the product of the two terms:
η
EO
is the electro-optical efficiency which accounts for
the steepness of the laser slope. It is the amount of the
extra optical output power in W/A of modulation current
optical output power.
R is the monitor photodiode responsivity. It is the
amount of the extra monitor photodiode current in A/W
optical output power.
τ
ONE
40
10
12
–
C
TONE
+
×
(
)
LASER
10
3
×
80
×
=
s
[ ]
B
ONE
π
τ
ONE
×
2
=
Hz
[
]
B
ONE
η
+
2
π
40
10
×
C
TONE
(
)
×
80
×
10
3
×
-------------------------------------------------------------------------------------------------
=
τ
ZERO
40
10
12
–
C
TZERO
+
×
(
)
LASER
10
3
×
50
×
=
s
[ ]
B
ZERO
1
ZERO
π
×
2
=
Hz
[
]
B
ZERO
η
+
2
π
40
10
–
C
TZERO
×
(
)
×
50
×
10
3
×
----------------------------------------------------------------------------------------------------
=
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