AK2572 Datasheet, PDF (14/50 Pages) Asahi Kasei Microsystems – APC for Burst Mode Applicable Direct Modulation Laser Diode

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
TEMPMON
BURST
EXTALM1
EXTALM2
/MOD_CTRL
Monitor
PD
Cpd
Rpd
TEMPALM threshold
V-DAC3 operation setting (RE_DAC_SET[2])
On-chip temperature sensor
offset adjusting
(RE_TEMP_OFFSET)
(E_TEMPALM)
TEMP
ALM
Tempalm
V-DAC3 gain setting (RE_DAC3_GAIN)
I-DAC1,V-DAC3 data selection
(RE_MODV_SEL) R_DAC3 _V-DAC3
VOUT3
EXTRA_DAC value (R_EXTRA)
Temp. sensor
ADC
(TEMPSENS)
(Time sharing) _Temperature
equivalent value
Burst mode setting (RE_BURST_SET)
(R_TEMP)
EEPROM
MOD: APC_FF value (R_MOD_FF)
+
MOD: APC_FB dividing ^{MOD data}
(RE_MOD_FBRT)
I-DAC1 operation setting
(RE_DAC_SET[0])
I-DAC1 gain setting
(RE_DAC1_GAIN)
IMOD
BURST_
CONTROL
Bｕｒｓｔ_ｃｔｒｌ
APC_FF setting
(RE_APC_FF_SET)
K_MOD
_FBRT
I-DAC1
R_DAC1
IOUT1
Pin setting
(RE_SFP_SET）
(RE_PWR_LVL1_SET）
EXTALM polarity setting
APC_FB initial value setting
(RE_EXTALM1_POL)
(RE_APC_INIT_SET)
(RE_EXTALM2_POL)
Power Leveling[1] setting
(RE_PWR_LVL1_SET)
EXTALM
Extalm1
Extalm2
(RE_SFP_SET)
Power Leveling[2] setting
(RE_PWR_LVL2_SET)
(RE_PWR_SEL)
Mod_Ctrl
APC_FB setting ^{BIAS: APC_FB dividing}
(RE_APC_FB_SET) ^{(RE_BIAS_FBRT)}
I-DAC2 operation setting
(RE_DAC_SET[1])
K_BIAS
I-DAC2 gain setting
(RE_DAC2_GAIN)
_FBRT
BIAS: APC_FF value
(R_BIAS_FF)
+
I-DAC2
BIAS data
(R_DAC2)
IBIAS
IOUT2
BIASMON
PDMON
PDGAIN setting
(RE_PDGAIN)
PDIN
PDGAIN
vpd
APC_
COMP
Digital Filter
1/N 1/s
OPALM threshold (RE_OPTALM)
APC_FB value
(R_APC_FB)
x 0.012
Over current threshold
(RE_CURRALM_MOD)
(RE_CURRALM_BIAS)
R_DAC1/R_DAC3
R_DAC2
CURRALM
Curralm
APC target
(RE_APC_TRGT)
DAC_APC
vapc_ref
ATT
optalm_ref
OPTALM
_COMP
Optalm
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