AK2572 Datasheet, PDF (17/50 Pages) Asahi Kasei Microsystems – APC for Burst Mode Applicable Direct Modulation Laser Diode

ASAHI KASEI
[AK2572]
4.2.3 DAC_APC
DAC_APC outputs APC_FB reference voltage (vapc_ref). vapc_ref is adjusted by RE_APC_TRGT.
The relation of RE_APC_TRGT and vapc_ref is shown in Table 4-4.
Table 4-4 DAC_APC Setting
R_APC_TRGT
DAC_APC output : vapc_ref ï¼»Typ.ï¼½
0 0000 (00h)
0.792 V
･･･
･･･
0 1111 (0Fh)
0.987 V
1 0000 (10h)
1 0001 (11h)
1.000 V
1.013 V
･･･
･･･
1 1111 (1Fh)
1.195 V
Note
13mV / step
4.2.4 APC_FB Dividing Function
The AK2572 has a function to divide the R_APC_FB value into both Bias current and Modulation current,
which is calculated by APC_FB function. By utilizing this function, the extinction ratio can be kept constant by
applying feedback operation on Bias and Modulation currents.
Block diagram in Figure 4-4 and the coefficient factor used for dividing calculation in Table 4-5 are shown.
Figure 4-4 APC Feedback Dividing Block Diagram
RE_MOD_FBRT
RE_DAC1_GAIN
(RE_DAC3_GAIN)
R_APC_FB
K_MOD
_FBRT
R_MOD_FB
I-DAC1
(V-DAC3)
Imod
(Vmod)
K_BIAS
_FBRT
R_BIAS_FB
I-DAC2
Ibias
RE_BIAS_FBRT
RE_DAC2_GAIN
Table 4-5 K_BIAS_FBRT, K_MOD_FBRT
RE_APC_FB_SET K_BIAS_FBRT
K_MOD_FBRT
Note
00 (0)
0
01 (1)
0
0
Without Feed Back (FB)
1
FB on Modulation current control only
10 (2)
1
0
FB on Bias current control only
11 （3）
R_BIAS_FBRT/128
R_MOD_FBRT/128
FB ratio is divided for both Bias and
Modulation currents [*]
[*] R_BIAS_FBRT≦127, R_MOD_FBRT≦127 (Be noted that full range of APC_FB current from I-DACs is
limited since the dividing coefficients are mutually multiplied)
4.3 APC Operation Setting
Combination of APC function is set by RE_APC_FF_SET and RE_APC_FB_SET. Setting examples are
shown in Table 4-6 and Figures 4-5 ~ 4-13. Handling of the data, which are retained in the temperature
compensated Bias data space (E_BIAS_TC) and the temperature compensated Modulation data space
(E_MOD_TC), is automatically altered by APC setting. Relation between APC setting and the data retained in
EEPROM space is listed in Table 4-7. As to the memory space of E_BIAS_TC and E_MOD_TC, please refer to
Table 9-3. Lists of the data for each APC combination are shown in Table 4-8 and 4-9.
RE_APC_FF_SET is configured with 2 bits and it selects the I-DAC for FF (Feed Forward) setting.
RE_APC_FB_SET is configured with 2 bits and it selects the I-DAC for FB (FeedBack) setting.
The upper bit shows the BIAS side and the lower bit shows the MOD (Modulation) side.
-17-
<MS0290-E-01>
2004/8