EVB71122
300 to 930MHz Receiver
Evaluation Board Description
2.2.2
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
nor the VCO inductor.
Low-low injection should be used for the high frequency bands. First of all choose a PFD frequency fPFD
according to below table. The R counter values are valid for a 10MHz crystal reference. The PFD frequency
is given by fPFD = fRO /R.
Injection Type
fCH [kHz]
20
fPFD [kHz]
16
R
l-l
l-l
l-l
l-l
l-l
l-l
625
500
250
125
50
25
20
50
40
100
250
500
80
200
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.
NLO2
4
fLO1
=
(fRF − fIF2 )
fLO1 = (fRF − 2MHz)
(8)
(9)
NLO2 +1
5
fRF + NLO2fIF2
NLO2 +1
fRF + 8MHz
fIF1
=
fIF1 =
5
Finally N and A can be calculated with formula (5).
2.2.3
Counter Setting Examples for SPI Mode
To provide some examples, the following table shows some counter settings for the reception of the well-
known ISM and SRD frequency bands. The channel spacing is assumed to be fCH = 100kHz. In below table
all frequency units are in MHz.
Inj
h-h
h-h
h-h
h-h
l-l
fRF
fIF1
fLO1
Ntot
N
P
A
4
fPFD
0.133
0.133
0.133
0.133
0.08
R
fREF
10
10
10
10
10
10
10
10
fLO2
99.3
fIF2
2
300
315
434
470
850
868
915
930
97.3 397.3 2980
102.3 417.3 3130
93
32
32
32
32
32
32
32
32
75
97
26
0
75
104.3
144
2
142
154
576
624
4320
4680
135
146
256
270
285
290
75
2
8
75
156
2
171.6 678.4 8480
175.2 692.8 8660
184.6 730.4 9130
187.6 742.4 9280
0
125
125
125
125
169.6
173.2
182.6
185.6
2
l-l
20
10
0
0.08
2
l-l
0.08
2
l-l
0.08
2
39012 71122 01
Rev. 001
Page 9 of 32
EVB Description
Sept/06
MELEXIS [ Melexis Microelectronic Systems ]
