mic3003gfltr Micrel Semiconductor, mic3003gfltr Datasheet - Page 26

• Manufacturer Part Number: mic3003gfltr
• Description: Fom Management Ic With Internal Calibration
• Manufacturer: Micrel Semiconductor

Micrel, Inc.
July 2010
Furthermore, the reference level for the APC circuit is
selectable to accommodate electrical, i.e., current
feedback, or optical feedback via a monitor photodiode.
Finally, any one of seven different internal feedback
resistors can be selected. This internal resistor can be
used alone or in parallel with an external resistor. This
wide range of adjustability (50:1) accommodates a wide
range of photodiode current, i.e., wide range of
transmitter output power. The APC operating point can
be kept near the mid-scale value of the APC DAC,
insuring maximum SNR, maximum effective resolution
for digital diagnostics, and the widest possible DAC
adjustment range for temperature compensation, etc.
See Figure 6.
The APCCAL bit in OEMCAL0 is used to turn the APC
function on and off. It will be turned on in the MIC3003’s
default state as shipped from the factory. When the APC
is on, the value in the selected APCSETx register is
added to the signed compensation value taken from the
APC look-up table and loaded into the V
the APC is off, the V
the V
This provides direct control of the laser diode bias during
setup and calibration. In either case, the V
setting is reported in the APCDAC register.
BIAS
Figure 5. APC and Modulation Control
register, bypassing the look-up table entirely.
BIAS
Block Diagram
DAC may be written directly via
BIAS
DAC. When
BIAS
DAC
26
Laser Modulation Control
As shown in Figure 5, a temperature-compensated DAC
is provided to set and control the laser modulation
current via an external laser driver circuit. The MODREF
bit in OEMCFG0 selects whether the V
swings up from ground or down from V
driver requires a voltage input to set the modulation
current, V
input is required, a fixed resistor can be used between
the driver and the V
configurations are possible as shown in Figure 8.
When the APC is on, i.e., the APCCAL bit in OEMCAL0
is set to 0, the value corresponding to the current
temperature is taken from the MODLUT look-up table,
added to the selected MODSETx register, and loaded
into the V
compensation value in V
V
provides for direct modulation control for setup and
calibration.
MOD
DAC, bypassing the look-up table entirely. This
Figure 6. Programmable Feedback Resistor
MOD
Figure 7. Transmitter Configurations
MOD
output can drive it directly. If a current
Supported by MIC3003
DAC. When the APC is off, the
[e-mail]
MOD
MOD
output. Several different
is loaded directly into the
or [phone]
MOD
M9999-072910-A
DD
MIC3003GFL
. If the laser
DAC output