EVB71122 Datasheet, PDF (9/32 Pages) Melexis Microelectronic Systems – 300 to 930MHz Receiver Evaluation Board Description

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 f_PFD
according to below table. The R counter values are valid for a 10MHz crystal reference. The PFD frequency
is given by f_PFD = f_RO /R.
Injection Type
f_CH [kHz]
f_PFD [kHz]
R
l-l
20
16
625
l-l
25
20
500
l-l
50
40
250
l-l
100
80
125
l-l
250
200
50
l-l
500
400
25
The second step is to calculate the missing parameters f_LO1, f_IF1, N_tot, N and A. While the second IF (f_IF2), the
N_LO2 divider ratio and the prescaler divider ratio P are bound to f_IF2 = 2MHz, N_Lo2 = 4 (or 8) and P =32.
PRELIMINARY ^fLO1
=
N _LO2
N _LO2 +
1
(f
RF
−
f _IF2 )
f _LO1
=
4
5
(f _RF
−
2MHz)
(8)
f _IF1
=
f _RF + N _LO2f _IF2
N _LO2 + 1
f _IF1
=
f _RF
+ 8MHz
5
(9)
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 f_CH = 100kHz. In below table
all frequency units are in MHz.
Inj
f_RF
f_IF1
f_LO1
N_tot
N
P
h-h 300 97.3 397.3 2980 93
32
h-h 315 102.3 417.3 3130 97
32
h-h 434 142 576 4320 135 32
h-h 470 154 624 4680 146 32
l-l 850 171.6 678.4 8480 256 32
l-l 868 175.2 692.8 8660 270 32
l-l 915 184.6 730.4 9130 285 32
l-l 930 187.6 742.4 9280 290 32
A
f_PFD
R
f_REF
f_LO2
f_IF2
4 0.133 75 10 99.3 2
26 0.133 75 10 104.3 2
0 0.133 75
10 144
2
8 0.133 75
10 156
2
0 0.08 125 10 169.6 2
20 0.08 125 10 173.2 2
10 0.08 125 10 182.6 2
0 0.08 125 10 185.6 2
39012 71122 01
Rev. 001
Page 9 of 32
EVB Description
Sept/06