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
l-l
l-l
l-l
l-l
l-l
l-l
f
CH
[kHz]
20
25
50
100
250
500
f
PFD
[kHz]
16
20
40
80
200
400
R
625
500
250
125
50
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.
f
LO1
=
f
IF1
=
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
h-h
h-h
h-h
h-h
l-l
l-l
l-l
l-l
f
RF
300
315
434
470
850
868
915
930
f
IF1
f
LO1
N
tot
N
P
A
4
26
0
8
0
20
10
0
f
PFD
R
f
REF
10
10
10
10
10
10
10
10
f
LO2
f
IF2
2
2
2
2
2
2
2
2
Y
R
A
IN
IM
L
E
R
P
f
RF
+
N
LO2
f
IF2
N
LO2
+
1
f
IF1
=
f
RF
+
8MHz
5
(9)
397.3
417.3
576
624
678.4
692.8
730.4
742.4
2980
3130
4320
4680
8480
8660
9130
9280
93
97
135
146
256
270
285
290
32
32
32
32
32
32
32
32
0.133
0.133
0.133
0.133
0.08
0.08
0.08
0.08
75
75
75
75
125
125
125
125
99.3
104.3
144
156
169.6
173.2
182.6
185.6
N
LO2
(f
RF
−
f
IF2
)
N
LO2
+
1
f
LO1
=
4
(f
RF
−
2MHz)
5
(8)
97.3
102.3
142
154
171.6
175.2
184.6
187.6
39012 71122 01
Rev. 001
Page 9 of 32
EVB Description
Sept/06
MELEXIS [ Melexis Microelectronic Systems ]
