ASAHI KASEI
[AK2572]
4. APC Functional Part
Circuit configuration of the APC part is shown in Figure 4-1. The AK2572 is formed with APC_FF function
which sets the programmed current with corresponding to the detected temperature by On-chip temperature
sensor and APC_FB function which controls with feedback function to keep the monitoring photo diode current
constant. By properly combining APC_FF and APC_FB functions together by EEPROM / Register setting, a
proper LD Bias current / Modulation current can be generated.
Figure 4-1 APC Circuit Block Diagram
V-DAC3 operation setting (RE_DAC_SET[2])
TEMPALM threshold
TEMPMON
TEMP
ALM
V-DAC3 gain setting (RE_DAC3_GAIN)
(E_TEMPALM)
Tempalm
On-chip temperature sensor
offset adjusting
(RE_TEMP_OFFSET)
I-DAC1,V-DAC3 data selection
R_DAC3
(RE_MODV_SEL)
V-DAC3
VOUT3
EXTRA_DAC value (R_EXTRA)
MOD: APC_FF value (R_MOD_FF)
Temp. sensor
ADC
(Time sharing)
I-DAC1 operation setting
(RE_DAC_SET[0])
(TEMPSENS)
EEPROM
+
Temperature
equivalent value
(R_TEMP)
MOD data
MOD: APC_FB dividing
I-DAC1 gain setting
(RE_DAC1_GAIN)
Burst mode setting (RE_BURST_SET)
(RE_MOD_FBRT)
IMOD
BURST_
CONTROL
K_MOD
_FBRT
APC_FF setting
(RE_APC_FF_SET)
BURST
Bｕｒｓｔ_ｃｔｒｌ
I-DAC1
R_DAC1
IOUT1
EXTALM polarity setting
(RE_EXTALM1_POL)
(RE_EXTALM2_POL)
BIAS: APC_FB dividing
APC_FB initial value setting
(RE_APC_INIT_SET)
APC_FB setting
I-DAC2 operation setting
(RE_DAC_SET[1])
I-DAC2 gain setting
(RE_DAC2_GAIN)
(RE_BIAS_FBRT)
(RE_APC_FB_SET)
Power Leveling[1] setting
(RE_PWR_LVL1_SET)
(RE_SFP_SET)
Power Leveling[2] setting
(RE_PWR_LVL2_SET)
(RE_PWR_SEL)
EXTALM1
K_BIAS
_FBRT
Pin setting
(RE_SFP_SET）
(RE_PWR_LVL1_SET）
Extalm1
Extalm2
IBIAS
EXTALM
Mod_Ctrl
+
I-DAC2
BIAS: APC_FF value
(R_BIAS_FF)
BIAS data
(R_DAC2)
IOUT2
EXTALM2
/MOD_CTRL
BIASMON
x 0.012
Digital Filter
APC_FB value
(R_APC_FB)
PDMON
APC_
1/N
1/s
PDGAIN setting
(RE_PDGAIN)
COMP
Over current threshold
(RE_CURRALM_MOD)
(RE_CURRALM_BIAS)
Monitor
PD
CURRALM
Curralm
PDIN
PDGAIN
R_DAC1/R_DAC3
R_DAC2
vpd
OPALM threshold (RE_OPTALM)
Cpd
Rpd
OPTALM
_COMP
Optalm
APC target
DAC_APC
ATT
(RE_APC_TRGT)
vapc_ref
optalm_ref
4. 1 APC_FF Function
APC_FF functional block diagram is shown in Figure 4-2. Output voltage of On-chip temperature sensor, which
responds to the detected temperature, is A-to-D converted (8 bits) in every temperature detection cycle (64 msec
[Typ.]). The resulting data (R_TEMP) is used as an EEPROM address and the data (8 bits) retained in
EEPROM at that address location is read out. The read out data is set to DAC and by supplying a proper
current to LD in response to temperature characteristics of each LD, APC_FF function is realized as in the
procedure above. Namely, the EEPROM address corresponds to temperature and the data corresponds to the
bias current and the modulation current at that temperature.
Although allocated EEPROM space for APC_FF is 7 bits (128 address locations), it is extended to 8 bits
equivalent data (256 address locations) by utilizing a linear interpolation of the current programming data as
shown in the following equation.
< Linear interpolation of E_BIAS_TC and E_MOD_TC>
Given that the detected temperature data are R_TEMP［7:0］＝z＝2x, 2x+1, R_TEMP［7:1］＝x, and the
temperature compensated data retained in EEPROM are E_BIAS_TC(x), E_MOD_TC(x), and the data
derived from linear interpolation are R_BIAS_FF(z), R_MOD_FF(z) respectively,
R_BIAS_FF(z)＝E_BIAS_TC(x－1)＋｛E_BIAS_TC(x)－E_BIAS_TC(x－1)｝×R_TEMP［0］/ 2
R_MOD_FF(z)＝E_MOD_TC(x－1)＋｛E_MOD_TC(x)－E_ MOD _TC(x－1)｝×R_TEMP［0］/ 2
But at x＝0 (R_TEMP［7:0］＝z＝0, 1), E_BIAS_TC(x)＝E_BIAS_TC(x－1)＝E_BIAS_TC(0)
E_MOD_TC(x)＝E_MOD_TC(x－1)＝E_MOD_TC(0)
-14-
<MS0290-E-01>
2004/8
AKM [ ASAHI KASEI MICROSYSTEMS ]
