AKM AK2571 User manual

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.
<Rev. 0.6E Preliminary> -1- 2001/11

AKM Confidential AK2571
Block Diagram
EEPROM
Store the
parameter and
look up table
I-DAC1
I-DAC2APC
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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AKM Confidential 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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AKM Confidential 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
+
IOUT3I-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-DAC1～3 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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AKM Confidential AK2571
3.1 Functional description
Block Function Note
T_V CONV Internal Temperature Sensor. Outputs a voltage that corresponds to the surface temperature
of the AK2571. This function controls temperature compensation of an external current
amplifier, driver IC, etc. By activating the E_APC_FF_SET (=1), the ADC outputs the digital
data of T_V CONV as the address of EEPROM stores the lookup table of temperature
compensation data for external components every 5.6degree. This data is output through
I-DAC and supplies the Laser Diode modulation and BIAS currents. If this function is not
required set E_APC_FF_SET to a fixed value and set the current value in E_DACx_FIX.
ADC 8-bits A-to-D converter for temperature detection. (5-bit MSB is used for temperature
compensation)
EEPROM E_APC_FF_SET=0 (Default): APC is not activated. Fixed data (E_DACx_FIX, x=1-3) is sent
to I-DACs.
E_APC_FF_SET=1: APC activation. 5-bits MSB of ADC sent to E_DACxTV[A/D], x=1-3
and work the APC sequence.
ADDER E_APC__FB_SET.Dacx(x=1-3)=0 (default): Do not add aging compensation current to
I-DACs.
E_APC_FB_SET.Dacx(x=1-3)=1: Add aging compensation (R_APC_CMPNST) current to
I-DACs.
I-DAC1 8-bit current output DAC (120mA max.). Output current corresponds to R_DAC1 data.
When R_DAC_SET=1, this outputs is enabled.
I-DAC2 8-bit current output DAC (20mA max.). Output current corresponding to R_DAC1 data.
When R_DAC_SET=1, this outputs is enabled.
I-DAC3 8 bit current output DAC (20mA max.). Output current corresponding to R_DAC1 data.
When R_DAC_SET=1, this outputs is enabled.
EA_MOD Dithering function. R_EA_SW=0: Non-Active/ 1: Active. R_EA_FREQ: Modulation
frequency selection: 16kHz(000), 32kHz(001), 64kHz(010), 128kHz(011) and 256kHz(100).
R_EA_GAIN: Additional level to I=DAC1 out selection:16%(00), 8%(01), 10.4%(10) and
2%(11).
PDGAIN Amplifies the input signal from the monitoring Photo Diode. (vpd).
Customers can set the gain from 0dB to 21dB(Typ.) by 0.7dB steps, using values stored in the
EEPROM.
Input range: 0.2V - 1.5V
Full-scale output through PDMON can be set from 0.4V to1.1V in 0.1V steps. Internal
attenuator adjusts the full scale per E_PDMON_SET..
DACAPC Generates the target APC (R_APC_TRGT) voltage (vact_ref) in proportion to PDGAIN.
APC_COMP Compares the PD monitoring voltage (vpd) with APC target voltage (vapc_ref), if vpd <
vapc_ref, outputs UP signals to digital filter. And if vpd > vapc_ref, outputs DOWN signals to
digital filter. The sampling rate is 512kHz.
DIGITAL
FILTER
Receives signals from APC_COMP, calculates the value to make vpd and vapc_ref equal. Its
value is the LD aging error (R_APC_CMPNST), and is limited by the value of
E_APC_FB_MAX. There is no need to supply negative current for aging error.
CUALM_COMP LD aging error current (R_APC_CMPNST) over Alarm value (E_CUALM_SET), output
CUALM. Its polarity is selected by register R_ALM_POL.
OPALM_GAIN OPALM (light sparkle fail) output level (vopalm_ref) setting by register R_OPALM_SET.
000: 1/2, 001: 1/3, 010: 1/4, 011: 1/5, 100: 1/6, 101:1/8
OPALM_COMP Compares the PD monitoring voltage (vpd) with OPALM voltage (vpalm), if vpd < vpalm,
outputs OPALM (light power down alarm). Its polarity is selected by register R_ALM_POL.
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AKM Confidential AK2571
3.2 Feed forward APC Function
The AK2571 compensates for ambient temperature variations caused by the current amplifier or driver chip located
outside of the LD module. If this function is not required, a fixed-current source for the LD can be used instead..
The Feed-forward process is described below:
1) The internal T_V converter (please refer to “3.6 Internal T-V converter”) senses the ambient temperature. The
integrated ADC converts the signal to a digital value.
2) 5-bit MSB data address for the EEPROM stores the temperature compensation data, which is sent to I-DACx.
3) Compensation current is output from I-DACx.
To execute feed forward APC, temperature compensation data must be stored in the internal EEPROM as a look-up table
that is programmed during the customer assembly process.
In Self-operation mode, all compensation operations (sensing T_V converter, access to EEPROM and compensation
current output through I-DACs) are automatically executed.
3.3 LD aging error compensation
Compensation current outputs are available for LD light power deterioration. APC_COMP compares the feedback voltage
from PDIN (vpd) with the output voltage of DACAPC (vapc_ref, R_APC_TRGT). Based on this result a compensation
current (R_APC_CMPNST) is added to the output current of I-DAC set by E_APC_FB_SET after averaging through a
digital filter.
LD Ageing error
compensation current
(R_APC_CMPNST)
PDGAIN
Monitor
PD
APC_
COMP
APC Target
(R_APC_TRGT)
PDIN
PDMON
RPD
CPD
DAC_APC
DIGITAL
FILTER
PD_MON Target
(R_PDMON_SET)
PD GAIN set
(R_PDGAIN)
LD Ageing compensation
Max value
(E_APC_FB_MAX)
PD voltage after
PDGAIN
(vpd)
vapc_ref
ADC*
PDMON Digital
(R_PDMOND)
*: Time shearing ADC
PDMON
set
3.3.1 PDMON / PDGAIN setting
Selects the output range from PDMON pin by R_PDMON_SET in the range from0.4 to 1.1V. Adjust the input signal level
using R_PD_GAIN (E_PD_GAIN) to make the initial input level equal the value of R_PDMON_SET. Table 3-2 indicates
the function of R_PDMON_SET and output voltages, Table 3-3 indicates the function of R_PDGAIN and Gain. After this
adjustment, the internal PD input voltage (vpd) is set at 1.8V(typ) in Self-operation mode.
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AKM Confidential AK2571
Table 3-2 R_PDMON_SET setting
R_PDMON_SET (E_PDMON_SET)[2:0] PDMON Full Scale
111 1.1V
- 0.1V / step
000 0.4V
Table 3-3 R_PDGAIN setting
R_PDGAIN_SET (E_PDGAIN_SET)[4:0] Gain
11111 21.7dB
- 0.7dB / step
00000 0dB
Make sure the PDMON voltage equals the value of R(E)_PDMON_SET.
Conversion expression: Gain = 20*log (1.8 / PDIN voltage)
3.3.2 DACAPC
Generates the reference voltage for aging compensation. Table 3-4 indicates the function of R(E)_APC_TRGT and vapc_ref
R_APC_TRGT (E_APC_TRGT)[6:0] Reference voltage for Aging compensation (vapc_ref)
1111111 2.1V
| 4.8mV / step
0000000 1.5V
Refer to “5.3.1 Process - ATC and APC Adjustment Example” for further instructions regarding the adjustment process, .
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AKM Confidential AK2571
3.4 Gain setting of I-DAC1,2,3
See the table below for a description on how to set the three I-DACs full-scale voltages. The resolution is set in proportion
with the gain.
I-DAC1 gain setting
R_DAC1_GAIN
(E_DAC1_GAIN)
Gain set value Max output
current (typ)
Setting range of
output current (typ)
Non missing code
warranty range (typ)
Current
resolution (typ)
00 1 121.8mA 30mA-121.8mA 30mA over 0.36mA
01 1/2 60.9mA 15mA-60.9mA 15mA over 0.18mA
10 1/4 30.45mA 7.5mA-30.45mA 7.5mA over 0.09mA
11 1/12 10.15mA 2.5mA-10.15mA 2.5mA over 0.03mA
I-DAC2 Gain setting
R_DAC1_GAIN
(E_DAC1_GAIN)
Gain set value Max output
current (typ)
Setting range of
output current (typ)
Non missing code
warranty range (typ)
Current
resolution (typ)
00(11) 1 20.42mA 0mA-21.42mA 2.5mA over 0.084mA
10 1/2 10.71mA 0mA-10.71mA 1.25mA over 0.042mA
11 1/4 5.36mA 0mA-5.36mA 0.625mA over 0.021mA
I-DAC3 Gain setting
R_DAC1_GAIN
(E_DAC1_GAIN)
Gain set value Max output
current (typ)
Setting range of
output current (typ)
Non missing code
warranty range (typ)
Current
resolution (typ)
00(11) 1 21.42mA 0mA-20.42mA 2.5mA over 0.084mA
10 1/2 10.71mA 0mA-10.71mA 1.25mA over 0.042mA
11 1/4 5.36mA 0mA-5.36mA 0.625mA over 0.021mA
<Rev. 0.6E Preliminary> -9- 2001/11

AKM Confidential AK2571
3.5 Modulation for dithering through I-DAC1
I-DAC1 has a modulation function for dithering. It’s added to the current of I-DAC1 and output through IOUT1. Its
function is available to set R_EA_SW.
Figure 3-3 shows the block diagram and Table 3-8 / 3-9 explains the setting
Figure 3-3 EA Block diagram
I-DAC1 IOUT1+
GAIN
EA gain set
(R_EA_GAIN)
EA frequency
set
(R_EA_FREQ)
Table 3-8 EA Dithering frequency
R_EA_FREQ
(E_EA_FREQ)
Setting frequency (Typ) Deviation (typ) Remarks
000 16kHz TBD (Default)
001 32kHz TBD
010 64kHz TBD
011 128kHz TBD
100-111 256kHz TBD
Table 3-9 Additional gain
R_EA_GAIN
(E_EA_GAIN)
Additional gain Deviation (typ) Remarks
00 16% TBD (Default)
01 8% TBD
10 4% TBD
11 2% TBD
<Rev. 0.6E Preliminary> -10- 2001/11

AKM Confidential AK2571
3.6 Internal T_V converter
The internal temperature sensor’s output voltage function is shown in Figure 3-4. This offset is different for each device,
and is adjusted during factory test by AKM. If re-adjustment of the offset is necessary (for higher accuracy, etc.), it is
possible to rewrite the R(E)_TV_OFFSET. Table 3-10 diagrams the offset voltage and R_TV_OFFSET. The internal T_V
converter has a gain of –12.3mV / degree (typ) and the 8-bit ADC (full scale is 2.2V) is changed 0.7degree for each LSB.
Actually, only 5bits MSB of ADC is valid for feed forward APC, so the compensation data is renewed every 5.6 degrees.
The internal T_V converter monitors the surface temperature of the AK2571 and detects any difference between this
temperature, the ambient temperature and the temperature of external components. It is possible to increase the accuracy
of this function by “training” the device beforehand and writing the compensation data trained as described below.
1) Single-point temperature adjustment
Read R_TV at one ambient temperature, and using the T_V Conv. Gain (-0.7degree/LSB), calculates the 8-bit ADC value
and enter it into the look-up table address for Feed forward APC.
By performing this training, the offset error can be cancelled. Of course this training must be executed in conjunction with
an APC adjustment. Please refer to 5.3.1 APC/ATC adjustment.
2) Two-point temperature adjustment
Read R_TV at two ambient temperatures, calculate the T_V Conversion gain. From this gain, calculate the 8-bit ADC
value and enter it into the look-up table address for Feed forward APC.
By performing this training, the offset error and gain variation can be cancelled. Of course this training must be executed in
conjunction with an APC adjustment. Please refer to 5.3.1 APC/ATC adjustment.
Figure 3-4 Internal Temperature Sensor
In te rn a l T e m p e ra tu re S e n s o r(T _V _C O N V ) (T y p c h a ra c te ristics)
V = -0.0123t + 1.5709
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
-40 0 40 80 120
Tem perature t [℃]
Output voltage
[
Shifed by offset adjustm ent
<Rev. 0.6E Preliminary> -11- 2001/11

AKM Confidential AK2571
Table 3-10 R_TV_OFFSET setting
R_TV_OFFSET[4:0]
E_TV_OFFSET[4:0]
Offset voltage [mV]
(Reference value)
11111 +375
11110 +350
11101 +325
| |
10001 +25
10000 0
01111 -25
| |
00010 -350
00001 -375
00000 -400
Default value of E_TV_OFFSET is set by AKM.
3.7 Example schematics of connect ion to external components
Figures 3-5 to 3-10 illustrate typical system connections. When connecting to a negative voltage source, use a level shifter to
ensure that the signal voltages stays within the specified range.. In addition to that, I-DAC1 can’t be forced negative voltage
supply.
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AKM Confidential AK2571
Figure 3-5 Figure-3-6
Direct Modulation with Positive Power Supply Direct Modulation with Negative Power Supply
I-DAC1
IOUT2
LD
I-DAC2
IOUT1
Driver Circuit
AK2571
LD Module
AK2571
VEE
I-DAC2
IOUT2
Driver circuit
VEE
I-DAC3
IOUT3
LD
LD-A
DC RF
Figure 3-7 Figure 3-8
Direct Modulation with Voltage Controlled LD Driver Direct Modulation with Voltage Controlled LD Driver
I-DAC1
IOUT2
LD
I-DAC2
IOUT1
Driner LSI
AK2571
BIAS
Current setting
Voltage
Modulation
Current setting
Voltage
AK2571
LD
DC
LD-A
RF
LD module
I-DAC2
IOUT2
I-DAC3
IOUT3
Driver circuit
VEE
VEE
BIAS
current set
voltage
Modulation
current set
voltage
Figure 3-9 Figure 3-10
EA Modulation EA with Voltage Controlled LD Drive
I-DAC1
LD-A
I-DAC2
LD
EA-A
EA
IOUT2
IOUT1
AK2571
I-DAC3
LD module with
EA modulator
IOUT3
Driner circuit
for EA
modulation
VEE
VEE
EA BIAS
current set
voltage
EA Modulation
current set
voltage
I-DAC1
VEE
I-DAC2
EA-A
IOUT2
IOUT1
AK2571
Driver Circuit
VEE
I-DAC3
LD module with
EA modulator
IOUT3
LD-A
LD
EA
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AKM Confidential AK2571
4. ATC (Automatic Temperature Compensation)
Figure 4-1 ATC Block diagram
OFFSET voltage
(R_ATC_OFFSET)
PID TEC_
CTRL
Regulator
Gain &
Offset
HEATP
COOLP
HEATN
COOLN
Rth
RL
ADC
Initial temperature
Target
(E_ATC_TRGT)
TEMPALM
COMP
Temperature alarm
threshold
(E_TMPRTALM_WIN)
PIDALM
COMP
PID ALM
threshold
(E_PIDALM_SET)
TEMPALM PIDALM
-
LD ageing error
current
(R_APC_CMPNST)
ATC_FB
ATC feed back
(R_ATC_CMPNST)
WLALM
COMP
ATC Feed back Alarm
(E_WLALM_SET)
WLALM
I-DAC4H
IOUT4C
REFOUT
TEMPIN
TEC
control
vtemp
I-DAC4C
IOUT4H
Temperature Target
(R_TMPRT__TRGT)
Parameter of ATC
feed back
(E_ATC_FB_SET)
Non sensed
value(E_PID_INACT)
PID max value(E_PID_MAX)
PID parameter
(E_PID_P,E_PID_I,E_PID_D)
TEC control way
(E_TEC_CTRL_SET)
(E_TEC_ANALOG) PWM devision
(R_TEC_PWM_SET)
ALM polarity
(R_ALM_POL) ALM polarity
(R_ALM_POL)
PID control
(R_PID_VALABS)
ALM polarity
(R_ALM_POL)
ATC_
LOCK
ATC_LOCK set
(E_LK_TMPRT_WIN)
-
Detect term set
(E_LK_CNT_SET)
Temperature data
(R_TMPRT_CRNT)
TECcontrol way
(E_TEC_CTRL_SET, E_TEC_ANALOG)
TECcontrol way
(E_TEC_CTRL_SET, E_TEC_ANALOG)
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AKM Confidential AK2571
4.1 ATC Block Explanation
Table 4-1 indicates the functions of the ATC block
Block Function Remarks
Regulator Supplies voltage to thermister included in the LD module. REFOUT=2.3V (typ). Thermister output
voltage (TEMPIN) error tracks the varying voltage supply temperature characteristics of REFOUT and
automatically calculates and cancels this in the AK2571.
Gain & Offset AK2571 amplifies (x13 typically) the input signal to enable higher resolution from the 8-bit ADC. The input
signal should be set to the midpoint of its full scale to meet the target temperature of the offset setting
function. For example, when thermister R0=10kohm.@25 degree, B=3900, load resistance 6.8kohm., its
sensitivity is about 0.03degree/LSB.
ADC 8b-it A-to-D converter. Reference voltage is 2.2V (typ). Temperature signal from Gain & OFFSET is
converted to digital and transferred to PID calculator.
PID Executes a PID (Proportion, Integration and differential) calculation to meet the temperature signal
(R_TMPRT_CRNT) at the target temperature (R_TMPRT_TRGT). Output data (R_PID_VALABS) is
composed of 13-bits absolute value and a positive/negative bit. Each PID parameter can be set in the
EEPROM. The cycle time for this calculation is 8mS (typ) and is set by the internal oscillator.
TEC_CTRL Using the PID data (R_PID_VALABS), the TEC (Thermo Electric Cooler) is controlled by PWM or
Analog control. When PWM control is selected, the FET switch is controlled through the PWM division set
register (R_TEC_PWM_SET).
I-DAC4H
I-DAC4C
10b-it current D-to-A converter. When analog control for TEC is selected, the IDAC outputs current
following 10bits MSB data from PID. Its full-scale output current is 50mA (typ). When Analog-1 is selected
(Control the current direction by FET: refer to figure 4-4), it is possible for I-DAC4H to output both cooling
and heating current, depending on current direction. On the other hand, when Analog-2 is selected,
heating current is output through I-DAC4H (I-DAC4C output is GND) and cooling current is output
through I-DAC4C (I-DAC4H output is GND).
ATC_FB Change the target temperature according to LD aging error from PD monitor voltage. Its value
(R_ATC_CMPNST) is calculated from the parameter (E_ATC_FB_SET). This function assumes that
there is first order function between the LD aging error and moving the wavelength to the longer, can
compensate wavelength shift cause from aging. When use this function, please note this assumption
carefully.
ATC_LOCK Detect the stabilization of LD temperature from start or reset of AK2571. The stabilization judge range
(E_LK_TMPRT_WIN) and its decision term (E_LK_CNT_SET) are set in EEPROM. If the LD
temperature data (R_TMPRT_CRNT) stays within the stabilization judge range for a period that is longer
than the decision term, the AK2571 moves to the next operation.
TEMPALMCOMP If the difference between LD temperature data (R_TMPRT_CRNT) and target temperature
(R_TMPRT_TRGT) exceeds the temperature alarm threshold (E_TEMPALM_WIN), TEMPALM is
triggered. RegisterI R_ALM_POL sets the polarity of this signal.
PIDALMCOMP When the PID control value (R_PID_VALUE) exceeds the PID alarm threshold (E_PIDALM_SET), PID
alarm is triggered. RegisterI R_ALM_POL sets the polarity of this signal
WLALMCOMP When the aging target temperature aging (R_ATC_CMPNST) is exceeds the threshold of the wavelength
aging error alarm (E_WLALM_SET), WLALM is output. Its polarity is selectable by the R_ALM_POL
register.
<Rev. 0.6E Preliminary> -15- 2001/11

AKM Confidential AK2571
4.2 PID control
Figure 4-2 explains the block diagram for PID control and table 4-3 indicates the parameter setting range
Figure 4-2 PID control
Temperature data
(R_TMPRT_CRNT)
Target temperature
(R_TMPRT_TRGT)
-
Z-1
Differencial
Parameter
(D)
+
Proportion
Parameter
(P)
Integration
Parameter
(I)
Σ
+
PID control value
(R_PID_VALABS)
E_PID_D E_PID_I
E_PID_P
PID integration
value
(R_PID_INTGRL)
Table 4-3: PID parameter setting range
Parameter EEPROM Min. Default Max.
Proportion E_PID_P 0 8 255
Integration E_PID_I 0 7/256 255/256
Differential E_PID_D 0 6/256 255/256
<Rev. 0.6E Preliminary> -16- 2001/11

AKM Confidential AK2571
4.3 TEC control
The TEC control process is illustrated in table 4-4. Figures 4-3 to 4-6 explain the circuit that drives TEC and table 4-5
indicate the pin strapping for different control modes.
Figure 4-3 PWM control Figure 4-5 Analog control 2-1
PID PWM
TEC
HEATP
COOLP
HEATN
COOLN
AK2571
PID
Curreny
direction
control
TEC
HEATP
COOLP
HEATN
COOLN
AK2571
IOUT4
I-DAC4
IOUT4B
Figure 4-4 Analog control-1 Figure 4-6 Analog control 2-2
PID
Current
direction
control
TEC
HEATP
COOLP
HEATN
COOLN
AK2571
Current
amp
IOUT4C
I-DAC4C
IOUT4H
I-DAC4H
PID
Currnt
direction
control
TEC
HEATP
COOLP
HEATN
COOLN
AK2571
IOUT4C
I-DAC4C
IOUT4H
I-DAC4H
Table 4-5 pin status
PID data TEC Control way IOUT4H IOUT4C HEAT_P HEAT_N COOL_P COOL_N
PWM GND GND 1 0 1 0
Analog-1 GND GND 1 0 1 0
PID=0 OFF
Analog-2 GND GND 1 0 1 0
PWM GND GND 0 PWM 1 0
Analog-1 Current out GND 0 1 1 0
PID>0 Heating
Analog-2 Current out GND 0 0 1 0
PWM GND GND 1 0 0 PWM
Analog-1 Current out GND 1 0 0 1
PID<0 Cooling
Analog-2 GND Current out 1 0 0 0
<Rev. 0.6E Preliminary> -17- 2001/11

AKM Confidential AK2571
Figure 4-7 PWM division
Operation cycle (8ms typ)
TS#1 TS#2 TS#3 TS#4
Minimum pulse width = 8ms/8192 ≅ 1us
Resolution=8192
Case-1
PID control value(R_PID_VALABS) = 2020
PWM division = 32
8192/32=256
64
TS#5 TS#6 TS#32
64 64 64 63 63 63
63
64
1us
256
Operation cycle (8ms typ)
TS#1 TS#2 TS#3
8192/16=128
32
32*36 + 31*28 = 2020
Case-2
PID control value(R_PID_VALABS) = 2020
PWM division = 64
64*4 + 63*28 = 2020
32 32
TS#4
32
TS#5
32
TS#6
32
TS#7
32
TS#8
32
TS#9
32 31 31 31
TS#64
31
TS#63TS#62TS#61
4.4 Gain & Offset
The AK2571 amplifies (typically x13) the input signal from the thermister to provide higher resolution for the 8-bit ADC. It
also adds an offset voltage to meet the middle of full scale at target temperature. Table 4-6 indicates temperature levels
that correspond to ADC values when using a thermister R0=10kohm@25degree, B=3900 and Table 4-7 indicates a
thermister R0=10kohm@25degree, B=3450. Both load resistances RL) are 6.8kohm, REFOUT is 2.3V. When adjusting
Offset voltage (R_ATC_OFFSET), target temperature must be a value between 96 (60h) and 160 (A0h).
<Rev. 0.6E Preliminary> -18- 2001/11

AKM Confidential AK2571
Table 4-6 Temperature corresponding to code of ADC (Thermister: R0=10kohm@25degree,B=3900)
Temperature [degree] (typ)
R_ATC_OFFSET Offset voltage
[V] ADC=0 ADC=96 ADC=128 ADC=160 ADC=256
0 0.30 -7.6 -3.2 -1.9 -0.6 3.0
1 0.33 -5.6 -1.5 -0.2 1.0 4.5
2 0.36 -3.8 0.2 1.4 2.6 5.9
3 0.39 -2.0 1.8 2.9 4.1 7.3
4 0.42 -0.3 3.3 4.4 5.5 8.7
5 0.45 1.3 4.7 5.8 6.9 10.0
6 0.48 2.8 6.2 7.2 8.3 11.3
7 0.51 4.3 7.5 8.6 9.6 12.5
8 0.54 5.7 8.9 9.9 10.9 13.8
9 0.57 7.1 10.2 11.2 12.2 15.0
10 0.60 8.5 11.5 12.5 13.4 16.2
11 0.63 9.8 12.7 13.7 14.6 17.4
12 0.66 11.1 14.0 14.9 15.8 18.5
13 0.69 12.4 15.2 16.1 17.0 19.7
14 0.72 13.6 16.4 17.3 18.2 20.9
15 0.75 14.8 17.6 18.5 19.4 22.0
16 0.78 16.0 18.8 19.6 20.5 23.2
17 0.81 17.2 19.9 20.8 21.7 24.3
18 0.84 18.4 21.1 21.9 22.8 25.4
19 0.87 19.6 22.2 23.1 24.0 26.6
20 0.90 20.7 23.4 24.2 25.1 27.7
21 0.93 21.9 24.5 25.4 26.2 28.8
22 0.96 23.0 25.6 26.5 27.4 30.0
23 0.99 24.1 26.8 27.6 28.5 31.1
24 1.02 25.3 27.9 28.8 29.6 32.2
25 1.05 26.4 29.0 29.9 30.8 33.4
26 1.08 27.5 30.2 31.0 31.9 34.5
27 1.11 28.7 31.3 32.2 33.1 35.7
28 1.14 29.8 32.4 33.3 34.2 36.9
29 1.16 30.9 33.6 34.5 35.4 38.1
30 1.19 32.1 34.7 35.6 36.6 39.3
31 1.22 33.2 35.9 36.8 37.7 40.5
32 1.25 34.4 37.1 38.0 38.9 41.7
33 1.28 35.6 38.3 39.2 40.2 43.0
34 1.31 36.7 39.5 40.4 41.4 44.3
35 1.34 37.9 40.7 41.7 42.6 45.6
36 1.37 39.1 42.0 42.9 43.9 46.9
37 1.40 40.3 43.2 44.2 45.2 48.3
38 1.43 41.6 44.5 45.5 46.5 49.7
39 1.46 42.8 45.8 46.8 47.9 51.1
40 1.49 44.1 47.2 48.2 49.3 52.5
41 1.52 45.4 48.5 49.6 50.7 54.0
42 1.55 46.7 49.9 51.0 52.1 55.6
43 1.58 48.1 51.3 52.5 53.6 57.2
44 1.61 49.5 52.8 54.0 55.1 58.8
45 1.64 50.9 54.3 55.5 56.7 60.6
46 1.67 52.3 55.9 57.1 58.4 62.3
47 1.70 53.8 57.5 58.7 60.1 64.2
<Rev. 0.6E Preliminary> -19- 2001/11

AKM Confidential AK2571
Table 4-6 Temperature levels corresponding to ADC values (Thermister: R0=10kohm@25degree,B=3450)
Temperature [degree] (typ)
R_ATC_OFFSET Offset voltage
[V] ADC=0 ADC=96 ADC=128 ADC=160 ADC=256
0 0.30 -11.3 -6.3 -4.7 -3.3 0.9
1 0.33 -9.2 -4.4 -2.9 -1.5 2.5
2 0.36 -7.1 -2.6 -1.2 0.2 4.0
3 0.39 -5.2 -0.8 0.5 1.8 5.6
4 0.42 -3.3 0.9 2.2 3.4 7.1
5 0.45 -1.5 2.5 3.7 5.0 8.5
6 0.48 0.2 4.0 5.3 6.5 10.0
7 0.51 1.8 5.6 6.8 8.0 11.4
8 0.54 3.4 7.1 8.2 9.4 12.7
9 0.57 4.9 8.5 9.7 10.8 14.1
10 0.60 6.5 10.0 11.1 12.2 15.4
11 0.63 7.9 11.4 12.5 13.6 16.8
12 0.66 9.4 12.7 13.8 14.9 18.1
13 0.69 10.8 14.1 15.2 16.3 19.4
14 0.72 12.2 15.4 16.5 17.6 20.7
15 0.75 13.5 16.8 17.8 18.9 22.0
16 0.78 14.9 18.1 19.1 20.2 23.3
17 0.81 16.2 19.4 20.4 21.5 24.6
18 0.84 17.5 20.7 21.7 22.8 25.8
19 0.87 18.9 22.0 23.0 24.1 27.1
20 0.90 20.2 23.3 24.3 25.3 28.4
21 0.93 21.5 24.6 25.6 26.6 29.7
22 0.96 22.7 25.8 26.9 27.9 31.0
23 0.99 24.0 27.1 28.1 29.2 32.3
24 1.02 25.3 28.4 29.4 30.5 33.6
25 1.05 26.6 29.7 30.7 31.8 34.9
26 1.08 27.9 31.0 32.0 33.1 36.2
27 1.11 29.1 32.3 33.3 34.4 37.5
28 1.14 30.4 33.6 34.6 35.7 38.9
29 1.16 31.7 34.9 35.9 37.0 40.3
30 1.19 33.0 36.2 37.3 38.4 41.6
31 1.22 34.3 37.5 38.6 39.7 43.0
32 1.25 35.7 38.9 40.0 41.1 44.5
33 1.28 37.0 40.3 41.4 42.5 45.9
34 1.31 38.3 41.6 42.8 43.9 47.4
35 1.34 39.7 43.0 44.2 45.4 48.9
36 1.37 41.1 44.5 45.6 46.8 50.4
37 1.40 42.5 45.9 47.1 48.3 52.0
38 1.43 43.9 47.4 48.6 49.8 53.6
39 1.46 45.3 48.9 50.1 51.4 55.3
40 1.49 46.8 50.4 51.7 53.0 57.0
41 1.52 48.3 52.0 53.3 54.6 58.8
42 1.55 49.8 53.6 55.0 56.3 60.6
43 1.58 51.4 55.3 56.7 58.1 62.4
44 1.61 53.0 57.0 58.4 59.9 64.4
45 1.64 54.6 58.8 60.2 61.7 66.4
46 1.67 56.3 60.6 62.1 63.6 68.5
47 1.70 58.0 62.4 64.0 65.6 70.7
<Rev. 0.6E Preliminary> -20- 2001/11