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MLX71122_16 Datasheet, PDF (19/59 Pages) Melexis Microelectronic Systems – 300 to 930MHz FSK/FM/ASK Receiver
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MLX71122
300 to 930MHz FSK/FM/ASK Receiver
Datasheet
3.1.2. Calculation of LO1 and IF1 frequency for Low Frequency Bands
High-high or high-low injection can be used for the low frequency bands. If equal channel steps are desired,
choose a PFD frequency fPFD according to the table below. The R counter values are valid for a 10MHz
crystal reference frequency fRO. The PFD frequency is given by fPFD = fRO /R.
Injection Type
h-h
h-h
h-h
h-h
h-h
h-h
h-h
fCH [kHz]
10
12.5
20
25
50
100
250
fPFD [kHz]
R
13.3
750
16.7
600
26.7
375
33.3
300
66.7
150
133.3
75
333.3
30
The second step is to calculate the missing parameters fLO1, fIF1, Ntot, N and A. While the second IF (fIF2), the
NLO2 divider ratio and the prescaler divider ratio P are bound to fIF2 = 2MHz, NLO2 = 4 (or 8) and P =32.
f LO1

N LO2
N LO2 
1
(f
RF
 fIF2 )
f LO1

4
3 (fRF
 2MHz)
(10)
f IF1

f RF  N LO2fIF2
N LO2  1
f IF1

f RF
 8MHz
3
(11)
Finally N and A can be calculated with equation (6).
3.1.3. Calculation of LO1 and IF1 frequency for High Frequency Bands
Typical ISM band operating frequencies like 868.3 and 915MHz can be covered without changing the
crystal or the VCO inductor. Low-low injection is usually used for the high frequency bands. If equal
channel steps are desired, choose a PFD frequency fPFD according to the table below. The R counter values
are valid for a 10MHz crystal reference. The PFD frequency is given by fPFD = fRO /R.
Injection Type
l-l
l-l
l-l
l-l
l-l
l-l
fCH [kHz]
20
25
50
100
250
500
fPFD [kHz]
R
16
625
20
500
40
250
80
125
200
50
400
25
The second step is to calculate the missing parameters fLO1, fIF1, Ntot, N and A. While the second IF (fIF2), the
NLO2 divider ratio and the prescaler divider ratio P are bound to fIF2 = 2MHz, NLo2 = 4 (or 8) and P =32.
f LO1

N LO2
N LO2 
1
(f
RF
 fIF2 )
f LO1

4
5 (fRF
 2MHz)
(12)
REVISION 014 – AUGUST, 2016
390 10 71122 01
Page 19 of 59
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