MICRF610TR MICREL [Micrel Semiconductor], MICRF610TR Datasheet - Page 15

• Manufacturer Part Number: MICRF610TR
• Description: 868-870 MHz ISM Band Transceiver Module
• Manufacturer: MICREL [Micrel Semiconductor]

Another application for which the RSSI could be used is to
determine if transmit power can be reduced in a system. If
the RSSI detects a strong signal, it could tell the
transmitter to reduce the transmit power to reduce current
consumption.
FEE
The Frequency Error Estimator (FEE) uses information
from the demodulator to calculate the frequency offset
between the receive frequency and the transmitter
frequency. The output of the FEE can be used to tune the
XCO frequency, both for production calibration and for
compensation for crystal temperature drift and aging.
The input to the FEE circuit are the up and down pulses
from the demodulator. Every time a ‘1’ is updated, an UP-
pulse is coming out of the demodulator and the same with
the DN-pulse every time the ‘0’ is updated. The expected
no. of pulses for every received symbol is 2 times the
modulation index (∆).
The FEE can operate in three different modes; counting
only UP-pulses, only DN-pulses or counting UP+DN
pulses. The no. of received symbols to be counted is either
8, 16, 32 or 64. This is set by the FEEC_0…FEEC_3
control bit, as follows:
Bit Synchronizer
0010101
0010110
A6..A0
Micrel, Inc.
December 2005
0000110
0000111 BitRate_clkS1 BitRate_clkS0 RefClk_K5 RefClk_K4
FEEC_1
FEEC_3
A6..A0
0
0
1
1
0
0
1
1
FEE_7
D7
-
FEEC_0
FEEC_2
FEE_6
D6
-
0
1
0
1
0
1
0
1
Table 8. FEEC Control Bit
D7
-
FEE_5
D5
-
FEE Mode
Off
Counting UP pulses
Counting DN pulses
Counting UP and DN pulses. UP
increments the counter, DN
decrements it.
No. of symbols used for the
measurement
8
16
32
65
FEE_4
D4
-
D6
‘0’
FEEC_3
FEE_3
D3
FEEC_2
FEE_2
D2
D5
‘0’
FEEC_1
FEE_1
D1
FEEC_0
FEE_0
D4
‘0’
D0
15
The result of the measurement is the FEE value, this can
be read from register with address 0010110b. Negative
values are stored as a binary no between 0000000 and
1111111. To calculate the negative value, a two’s
complement of this value must be performed. Only FEE
modes where DN-pulses are counted (10 and 11) will give
a negative value.
When the FEE value has been read, the frequency offset
can be calculated as follows:
where FEE is the value stored in the FEE register, (Fp is
the single sided frequency deviation, P is the number. of
symbols/data bit counted and R is the symbol/data rate. A
positive Foffset means that the received signal has a
higher frequency than the receiver frequency. To
compensate for this, the receivers XCO frequency should
be increased.
It is recommended to use Mode UP+DN for two reasons,
you do not need to know the actual frequency deviation
and this mode gives the best accuracy.
BitSync_clkS2 BitSync_clkS1 BitSync_clkS0 BitRate_clkS2
RefClk_K3
D3
Mode UP:
Mode DN:
Mode UP+DN: Foffset = R/(4P)x(FEE)
RefClk_K2
D2
Foffset = R/(2P)x(FEE-∆Fp)
Foffset = R/(2P)x(FEE+∆Fp)
RefClk_K1
D1
M9999-120205
RefClk_K0
MICRF610
D0