AKM Confidential
AK2571
= Preliminary = AK2571
Single-Chip Automatic Power/Temperature Control
for WDM Laser Diodes
Features
Single Chip LSI that integrates APC (Auto Power Control) and ATC (Auto Temperature Control) functions for
WDM Laser Module
A controlling TEC (Thermal Electrical Cooler) stabilizes the temperature of LD module in the range of +/-0.1
C
by PID algorithm.
Parameters controlling Laser Diode are user programmable and stored in EEPROM
Internal Temperature Sensor detects on-chip temperature, enabling compensation internal and external
components that may be affected by changing ambient temperature.
Autonomous operation (internal oscillator and logic).
Pin-selectable wavelength data for tunable laser diodes (four options).
Single 3.3V operation
64-pin LQFP or Bare chip
Description
The AK2571 is a single-chip solution for WDM Laser Diode Module applications. It integrates both ATC (Auto
Temperature Control) and APC (Auto Power Control) functions in a small 64-pin LQFP or bare die package..
The ATC function of the AK2571 detects the LD module temperature via an external thermister and uses the PID
algorithm to control the Thermo-Electric Cooler (TEC). This provides +/- 0.1
C stabilization.. A customer can program the
appropriate PID parameters into the internal EEPROM , thereby providing compensation characteristics for each Laser
Diode. TEC control is handled through either PWM or Analog current control through I-DAC4. These are easily selected
by an EEPROM (Register) setting.
The APC has two functions. The first function is to compensate for Laser Diode power decreases caused by aging. The
other function is to compensate for temperature variations of AK2571 and external components (current amplifier or
driver circuits) which may be affected by ambient temperature within the LDM. The AK2571 does this by controlling
BIAS and modulation current according to the look up table in EEPROM .
The AK2571 has every alarm needed for WDM modules (Loss of power, Over current, Temperature etc.). There is a
dithering function for modulation current that improves the extinction ratio for long distance transmissions.
Also, parameter and compensation data can be stored for four wavelengths. If a customer uses a tunable laser diode, it is
very easy to change the wavelength by pin control.
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AK2571
Block Diagram
EEPROM
Store the
parameter and
look up table
I-DAC1
I-DAC2
APC
PID
PWM
or
Current
direction
control
TEC
Driver
+
LD
Alarm Decision
OPALM(Optical out down)
HEATP
COOLP
COOLN
HEATN
Digital I/F
OSC
AK2571 - Block Diagram -
Monitor
DAC
AMON
I-DAC4
Curret
Amp/
Bypass
CUALM(Over Current)
TEMPALM(Temperature ALM
PIDALM(TECControl current ALM)
WLALM(Target Temperature ALM)
IOUT1
IOUT3
IOUT4H
CSN
SKN
DI
DO
WAVE1
WAVE0
I-DAC3
IOUT2
SHUT_APCN
SHUT_ATCN
IOUT4C
BIAS GEN
BIAS
READY
TIMERALM
MODE
STATUS
REG
EEP
RB (12k)
STATUS_MON
T-V
Conv.
Gain &
OFFSET
Adj
Regulator
ADC
Selecter
Rth
TEMPIN
REFOUT
RL
Gain Adj
Monitor
PD
PDIN
PDMON
RPD
CPD
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AKM Confidential
AK2571
Circuit Description
1. Over
view
The AK2571 has two primary functions. The first function is APC (Automatic Temperature Control) which supplies
adequate modulation /BIAS current to a Laser diode and the other is ATC (Automatic Temperature control) which
controls the TEC (Thermo Electric Cooler) to stabilize the temperature of the Laser diode.
1. 1 APC
There are three Digital to Analog Converters (I-DAC1, 2, 3) that output the current for modulation, BIAS and EA
(Electrical Absorption) Modulation.
Maximum output currents :
I-DAC1: 120mA (typ.),
I-DAC2 and I-DAC3: 20mA (typ.)
Each DAC has a current limit function whose value is stored in the internal EEPROM. This is especially important for
I-DAC1, which has the modulation function for dithering.
In WDM systems, there is no need for discrete laser diode temperature compensation. However the outer current
amplifier or LD drivers may be affected by ambient temperature changes. In order to compensate for these the AK2571
has a feed-forward APC that can supply adequate current corresponding to the ambient temperature change detected by
the internal T_V converter.
Please refer the part "3. APC" for details.
1.2 ATC
The AK2571 controls TEC to stabilize the input voltage from the temperature sensor of the LD module (Thermistor). The
control algorithm is PID (Proportion Integration Differential) which has user-programmable parameters that are stored in
EEPROM. There are two ways for driving TEC, one is PWM (more energy effective than DC drive), the other is DC
current drive through I-DAC, which has lower noise.
Please refer the part "4. ATC" for details.
1.3 Control Sequence
There are three functional modes in AK2571 below.
1) Self-operation mode: The AK2571 operates ATC and APC independently. When self-operating mode starts, , ATC Lock
(detects when the target temperature is reached), APC Count up (prevents jumps in BIAS and Modulation currents) and
Timer (counts the time from device start to beginning of operation) are available.
2) Register Access Mode: AK2571 permits writing registers through the digital interface. Customers can adjust any
parameters or tables in this mode.
3) EEPROM mode: AK2571 permits EEPROM writes. Customers can store the parameters or table data in EEPROM.
Please refer the part "5. Sequencer" for details.
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AK2571
2. Reference
2.1 Definition
All values are expressed in the order shown below
Tab_(Function Block_)Main name(Function_).Sub name[Bit]
Setting way
Tab
Main name
Sub name
Bits
Example
Register R
REGISTER
NAME
(Capital letter)
Sub register name
[x,x]
R_PDGAIN
R_DAC_SET.Dac1
R_DAC_SET[2:0]
EEPROM E
EEPROM
NAME
(Capital letter)
Sub eeprom name
[x,x]
E_PDGAIN
E_DAC_SET.Dac1
PIN
P
PIN NAME (Capital
letter)
P_WAVE0
Register and EEPROM names may include additional tags as described below
Classify Additional
Tag
Contents
Example
APC APC
relate
E_APC_FF_SET
DAC I-DAC
relate
E_DAC1_FIX
ATC ATC
relate
E_ATC_OFFSET
ALM Alarm
relate
E_ALM_POL
PID PID
relate
E_PID_P
LK
ATC Lock counter relate
E_LK_CNT_SET
Function Block
TMPRT Temperature
decode value
R_TMPRT_TRNT
SET
Settled value (ALM or Counter etc.)
E_DAC1_SET
WIN
Hysteresis (ALM or counter etc.)
E_TMPRTALM_WIN
CTRL
Hysteresis (ALM or counter etc.)
E_INI_CTRL_USR
FIX
Fixed data for APC
E_DAC1_FIX
TV
APC compensation data
E_DAC1_TV
CMPNST
LD aging compensation data
R_APC_CMPNST
TRGT
Target value (Temperature or Voltage etc.)
E_APC_TRGT
CRNT Current
value
R_TMPRT_CRNT
Function
BFR Before
value
R_TMPRT_BFR
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AK2571
All circuit blocks and internal nodes are noted as below
Main
name
Example
Circuit Block
BLOCK NAME (Capital letter)
I-DAC1
PID
Internal Node
Signal name (Small letter)
vout
2.2 Functional explanation
Some values are stored in both register and EEPROM to simplify user programming. Explanations of these values are in
the register description tables.
For EEPROM details, refer to Section 7. EEPROM
For Register details, refer to Section 8. Registers
3. APC (Automatic Power Control)
I-DAC2
IOUT2
OPALM
T-V_
CONV
ADC*
EEPROM
I-DAC1
IOUT1
CUALM_
COMP
Current ALM set
(E_CUALM_SET)
CUALM
LD Ageing
compensation current
(R_APC_CMPNST)
PDGAIN
Monitor
PD
APC_
COMP
APC Target
(R_APC_TRGT)
OPALM_
COMP
Optical out down
threshold(R_OPALM_SET)
PDIN
+
IOUT3
I-DAC3
ADDER
PDMON
RPD
CPD
DAC_APC
OPALM_
GAIN
DIGITAL
FILTER
R_DAC1
R_DAC2
R_DAC3
APC set
(E__APC_FF_SET)
EA_MOD
LD Ageing
compensation
ON/OFF
(E__APC_FB_SET)
PD_MON Target
(R_PDMON_SET)
PD GAIN set
(R_PDGAIN)
ALM polarity set
(R_ALM_POL)
ALM polarity
set
(R_ALM_POL)
LD ageing compensation
current limit value
(E_APC_FB_MAX)
I-DAC13 ON/
OFF(R__DAC_SET[2:0])
I-DAC1 Gain set
(R_DAC1_GAIN)
EA_MOD ON/OFF(R_EA_SW)
Frequency(R_EA_FREQ)
Gain(R_EA_GAIN)
I-DAC2 Gain set
(R_DAC2_GAIN)
I-DAC3 Gain set
(R_DAC3_GAIN)
PD voltage after
PDGAIN
(vpd)
vapc_ref
vopalm_ref
ADC*
PDMON Digital value
(R_PDMOND)
* Time shearing ADC
PDMON
set
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