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參數(shù)資料
| 型號： | VSC7939 |
| 廠商： | Vitesse Semiconductor Corporation. |
| 英文描述： | Laser Diode Driver with Automatic Power Control |
| 中文描述： | 激光二極管驅(qū)動器，帶有自動功率控制 |
| 文件頁數(shù)： | 11/18頁 |
| 文件大小： | 226K |
| 代理商： | VSC7939 |
VITESSE
Preliminary Data Sheet
VSC7939
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
G52350-0, Rev 3.2
02/26/01
Page 11
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano
Camarillo, CA 93012
Tel: (800) VITESSE
FAX: (805) 987-5896
Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Laser Diode Interface
An RC shunt network should be placed at the laser output interface. The sum of the resistor placed at the
output and the laser diode resistance should be 25
. For example, if the laser diode has a resistance of 5
, a
20
resistor should be placed in series with the laser. For optimal performance, a bypass capacitor should be
placed close to the laser anode.
A
“
snubber network
”
consisting of a capacitor C
F
and resistor R
F
should be placed at the laser output to
minimize reflections from the laser (see Block Diagram). Suggested values for these components are 80
and
2pF, respectively, however, these values should be adjusted until an optical output waveform is obtained.
Reducing Pattern-Dependent Jitter
Three design values significantly affect pattern-dependent jitter; the capacitor at CAPC, the pull-up induc-
tor at the output (L
P
), and the AC-coupling capacitor at the output (C
D
). As previously stated, the recommended
value for the capacitor at CAPC is 0.1
μ
F. This results in a 10kHz loop bandwidth which makes the pattern-
dependent jitter from the APC loop negligible.
For 2.5Gb/s data rates, the recommended value for C
D
is 0.056
μ
F. The time constant at the output is domi-
nated by L
P
. The variation in the peak voltage should be less that 12% of the average voltage over the maximum
consecutive identical digit (CID) period. The following equation approximates this time constant for a CID
period, t, of 100UI = 40ns:
τ
LP
= -t / ln(1-12%) = 7.8t = L
P
/ 25
Therefore, the inductor L
P
should be a 7.8
μ
H SMD ferrite bead inductor for this case.
Input/Output Considerations
Although the VSC7939 is PECL-compatible, this is not required to drive the device. The inputs must only
meet the common-mode voltage and differential voltage swing specifications.
Power Consumption
The following equation provides the device supply current (I
S
) in terms of quiescent current (I
Q
), modula-
tion current (I
MOD
), and bias current (I
BIAS
):
I
S
= I
Q
+ 0.47 * I
MOD
+ 0.15 * I
BIAS
For 3.3V operation, I
Q
is 15mA. For 5V operation, I
Q
is 20mA.
This equation may be used to determine the estimated power dissipation:
P
DIS
= V
CC
* I
S
For example, if the device were operated at 3.3V with a 30mA modulation current and a 10mA bias current,
the supply current would be:
I
S
= 15mA + 0.47 * 30mA + 0.15 * 10mA = 31
This corresponds to a power dissipation of 3.3V * 31mA = 102mW.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| VSC7939RP | 制造商:VITESSE 制造商全稱:Vitesse Semiconductor Corporation 功能描述:Laser Diode Driver with Automatic Power Control |
| VSC7939W | 制造商:VITESSE 制造商全稱:Vitesse Semiconductor Corporation 功能描述:Laser Diode Driver with Automatic Power Control |
| VSC7940 | 制造商:VITESSE 制造商全稱:Vitesse Semiconductor Corporation 功能描述:SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control |
| VSC7940RP | 制造商:VITESSE 制造商全稱:Vitesse Semiconductor Corporation 功能描述:SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control |
| VSC7940W | 制造商:VITESSE 制造商全稱:Vitesse Semiconductor Corporation 功能描述:SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control |
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