MIC3002_10 Datasheet, PDF (25/65 Pages) Micrel Semiconductor – FOM Management IC with Internal Calibration

Micrel, Inc.
MIC3002
Figure 3. Internal Calibration RX Power Linear Approximation
Temperature Offset
In both internal and external calibration, the temperature
offset is set in the temperature reading compensation LUT
(see subsection above). Bit 5 in OMCFG5 (A6:1Ah) must
be set to 1 in order to enable temperature reading
compensation. Since the resolution of that L.U.T. is 0.5ºC,
the entered value should be twice the real value. For
example, if the content of the L.U.T. is 0 for all the entries
and the offset is 5ºC, then the offset value to be added to
the entries content is 10. The new content of the L.U.T.
entries will be 0+10=10.
C/ ADC Result Registers Reading
The ADC result registers should be read as 16-bit registers
under internal calibration while under external calibration
they should be read as 8-bit or 16-bit registers at the MSB
address. For example, TX power should be read under
internal calibration as 16 bits at address A2h: 66–67 and
under external calibration as 8 bits at address A2h: 66h. 9-
bit temperature results and 12-bit receive power results
should always be read as 16-bit quantities.
RXPOT
A programmable, non-volatile digitally controlled
potentiometer is provided for adjusting the gain of the
receive power measurement signal chain in the analog
domain. Five bits in the RXPOT register are used to set
and adjust the position of potentiometer. RXPOT functions
as a programmable divider or attenuator. It is adjustable in
steps from 1:1 (no divider action) down to 1/32 in steps of
1/32. If RXPOT is set to zero, then the divider is bypassed
completely. There will be no scaling of the input signal, and
the resistor network will be disconnected from the VRX pin.
At all other settings of RXPOT, there will be a 32kΩ (typical)
load seen on VRX.
Figure 4. RXPOT Block Diagram
Laser Diode Bias Control
The MIC3002 can be configured to generate a constant bias
current using electrical feedback, or regulate average
transmitted optical power using a feedback signal from a
monitor photodiode, refer to Figure 5. An operational
amplifier is used to control laser bias current via the V_BIAS
output. The VBIAS pin can drive a maximum of ±10mA. An
external bipolar transistor provides current gain. The polarity
of the op amp’s output is programmable BIASREF in
OEMCFG1 in order to accommodate either NPN or PNP
transistors that drive common anode and common cathode
laser, respectively. Additionally, the polarity of the feedback
signal is programmable for use with either common-emitter
or emitter-follower transistor circuits.
July 2007
25
M9999-073107-B
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