MIC3002_10 Datasheet, PDF (23/65 Pages) Micrel Semiconductor – FOM Management IC with Internal Calibration

Micrel, Inc.
RX Power
Received power is sensed as a voltage appearing at
VRX. It is assumed that this voltage is generated by a
sense resistor carrying the receiver photodiode current
or by the RSSI circuit of the receiver. The value returned
by the A/D is therefore a voltage analogous to received
power. The binary values in RXOPh and RXOPl are
related to receive power by:
RX(mW) = K x VREF x (256 x RXOPh +RXOPl/16)/
65536
(4)
For a given implementation, the constant, K, will likely
have to be determined through experimentation or
closed-loop calibration, as it depends upon the gain and
efficiencies of the receiver. In SFF-8472
implementations, the external calibration constants can
describe up to a fourth-order polynomial in case K is
nonlinear.
B/ Internal Calibration
If the INTCAL bit in OEMCFG3 is set to 1 (internal
calibration selected), the MIC3002 will process each
piece of data coming out of the A/D converter before
storing the result in memory. Linear slope/offset
correction will be applied on a per-channel basis to the
measured values for voltage, bias current, TX power,
and RX power. Only compensation is applied to
temperature.
The user must store the appropriate slope/offset
parameters in memory at the time of transceiver
calibration. In the case of RX power, a look-up table is
provided that implements eight-segment piecewise-
linear correction. This correction may be performed as a
compensation of the receiver non-linearity over receive
power level. If static slope/offset correction for RX power
is desired, the eight coefficient sets can simply be made
the same. The memory maps for these coefficients are
shown in Tables 11 and 12. The user must enter the
seven delimiters of the intervals that fit better the
receiver response. The diagram in Figure 3 shows the
link between the delimiters and the sets of
slopes/offsets.
The slopes allow for the correction of gain errors. Each
slope coefficient is an unsigned, sixteen-bit, fixed-point
binary number in the format:
[mmmmmmmm.llllllll], where m is a data bit (5)
in the most-significant byte and l is a data
bit in the least significant byte
Slopes are always positive. The binary point is in between
the two bytes, i.e., between bits 7 and 8. This provides a
numerical range of 1/256 (0.00391) to 255.997 in steps of
1/256. The most significant byte is always stored in
memory at the lower numerical address.
July 2007
MIC3002
The offsets correct for constant errors in the measured
data. Each offset is a signed, sixteen-bit, fixed-point
binary number. The bit-weights of the offsets are the
same as that of the final results. The sixteen-bit offsets
provide a numerical range of –32768 to +32767 for
voltage, bias current, transmit power, and receive power.
The numerical range for the temperature offset is
–32513 (–128°) to +32512 (+127°) in increments of 256
(1°). The format for offsets is:
[Smmmmmmmllllllll], where S is the sign bit (6)
(0 = positive, 1 = negative), m is a data bit in
the most-significant byte and l is a data bit in
the least significant byte
The most significant byte is always stored in memory at
the lower numerical address.
Calibration of voltage, bias current, and TX power are
performed using the following calculation:
RESULTn = ADC_RESULTn x SLOPEn + (7)
OFFSETn
Calibration of RX power is performed using the following
calculation:
RESULT = ADC_RESULT x SLOPE(m) + (9)
OFFSET(m)
where m represents one of the eight linearization
intervals corresponding to the RX power level.
The results of these calculations are rounded to sixteen
bits in length. If the seventeenth most significant bit is a
one, the result is rounded up to the next higher value. If
the seventeenth most significant bit is zero, the upper
sixteen bits remain unchanged. The bit-weights of the
offsets are the same as that of the final results. For SFF-
8472 compatible applications, these bit-weights are
given in Table 10.
Parameter
Voltage
Bias Current
TX Power
RX Power
Magnitude of LSB
100µV
2µA
0.1µW
0.1µW
Table 10. LSB Values of Offset Coefficients
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M9999-073107-B
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