參數(shù)資料
型號(hào): DS1878T+T&R
廠商: Maxim Integrated Products
文件頁(yè)數(shù): 7/101頁(yè)
文件大?。?/td> 0K
描述: IC CTLR SFP W/DGTL LDD RX 28TQFN
標(biāo)準(zhǔn)包裝: 2,500
類型: SFP+ 控制器
輸入類型: 模擬,數(shù)字
輸出類型: 數(shù)字
接口: I²C,LDD,串行
電流 - 電源: 2.5mA
安裝類型: 表面貼裝
封裝/外殼: 28-WFQFN 裸露焊盤
供應(yīng)商設(shè)備封裝: 28-TQFN-EP(5x5)
包裝: 帶卷 (TR)
BIAS Register/APC Control, 3-Wire Mode
A Maxim laser driver controls its laser bias current DAC
using the APC loop within the device. The APC loop’s
feedback to the device is the monitor diode (MON2)
current, which is converted to a voltage using an exter-
nal resistor. The feedback is sampled by a comparator
and compared to a digital set-point value. The output of
the comparator has three states: up, down, or no-oper-
ation. The no-operation state prevents the output from
excessive toggling once steady state is reached. As
long as the comparator output is in either the up or
down states, the bias is adjusted by writing increment
and decrement values to the Maxim laser driver
through the BIASINC register.
The device has an LUT to allow the APC set point to
change as a function of temperature to compensate for
tracking error (TE). The APC LUT has 36 entries that
determine the APC setting in 4°C windows between
-40°C and +100°C.
MODULATION Control
A Maxim laser driver controls the laser modulation
using the internal temperature-indexed LUT within the
device. The modulation LUT is programmed in 2°C
increments over the -40°C to +102°C range to provide
temperature compensation for the laser’s modulation.
The modulation is updated after each temperature con-
version using the 3-wire interface that connects to the
Maxim laser driver. A Maxim laser driver include a 9-bit
DAC. The modulation LUT is 8 bits.
Figure 1 demonstrates how the 8-bit LUT controls the
9-bit DAC with the use of a temperature control bit
DS1878
______________________________________________________________________________________
13
Table 1. Acronyms
ACRONYM
DEFINITION
ADC
Analog-to-Digital Converter
AGC
Automatic Gain Control
APC
Automatic Power Control
APD
Avalanche Photodiode
ATB
Alarm Trap Bytes
BM
Burst Mode
DAC
Digital-to-Analog Converter
DFB
Distributed Feedback Laser
LDD
Laser Diode Driver
LOS
Loss of Signal
LUT
Lookup Table
NV
Nonvolatile
QT
Quick Trip
TE
Tracking Error
TIA
Transimpedance Amplifier
ROSA
Receiver Optical Subassembly
SEE
Shadowed EEPROM
SFF
Small Form Factor
SFF-8472
Document Defining Register Map of SFPs
and SFFs
SFP
Small Form Factor Pluggable
SFP+
Enhanced SFP
TOSA
Transmit Optical Subassembly
TXP
Transmit Power
VCSEL
Vertical Cavity Self-Emitting Laser
SFP+ Controller with Digital LDD Interface
MOD LUT
LOADED TO [7:0]
MOD LUT
LOADED TO [7:0]
MODTI
8
7
6
5
4
3
2
1
0
MODTI
MODTC = 0
TEMPERATURE (
°C)
-40
+102
TEMPERATURE (
°C)
-40
+102
MODTC = 1
MOD LUT
LOADED TO [8:1]
(DAC BIT 0 = 0)
MOD LUT
LOADED TO [8:1]
(DAC BIT 0 = 0)
MAX3798
DAC
BIT
8
7
6
5
4
3
2
1
0
MAX3798
DAC
BIT
Figure 1. Modulation LUT Loading to a Maxim Laser Driver MOD DAC
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