EVB71112 Melexis Company, EVB71112 Datasheet - Page 5

• Manufacturer Part Number: EVB71112
• Description: Evaluation Board For Th71112
• Manufacturer: Melexis Company

By configuring the TH71112 for double conversion and using its internal PLL synthesizer with fixed feedback
divider ratios of N1 = 16 (DIV_16) and N2 = 2 (DIV_2), four types of down-conversion are possible: low-side
injection of LO1 and LO2 (low-low), LO1 low-side and LO2 high-side (low-high), LO1 high-side and LO2
low-side (high-low) or LO1 and LO2 high-side (high-high). The following table summarizes some equations
that are useful to calculate the crystal reference frequency (REF), the first IF (IF1) and the VCO1 or first LO
frequency (LO1), respectively, for a given RF and second IF (IF2).
1.6.1
The following table depicts crystal, LO and image signals considering the examples of 868.3 MHz and
915 MHz RF reception at IF2 = 10.7 MHz. The columns in bold depict the selected frequency plans to
receive at 868.3 MHz and 915 MHz, respectively.
1.6.2
39012 71112 01
Rev. 012
IF1 image/MHz
RF image/MHz 961.24667 746.00588
Injection type high-high
Signal type
REF / MHz
LO1 / MHz
LO2 / MHz
Injection type
IF1 / MHz
Injection type
Parameter
REF / MHz
LO1 / MHz
LO2 / MHz
IF1 / MHz
RF / MHz
IF2/ MHz
Selected Frequency Plans
Maximum Frequency Coverage
REF
LO1
LO2
IF1
IF2
914.77333 807.15294
28.58667
46.47333
57.17333
67.87333
868.3
RF =
MHz
high-low
739.3
25.0
60.7
50.0
10.7
(RF – IF2)/30
800
f
min
high-high
LO2 – IF1
LO1 – RF
32•REF
low-low
25.22353
61.14706
50.44706
39.74706
2•REF
868.3
RF =
MHz
high-low
1006.9
998.825
29.0625
868.3
low-low
RF =
937.6
MHz
68.825
58.125
29.3
69.3
58.6
47.9
10.7
f
930
max
(RF – IF2)/34
IF1 – LO2
RF – LO1
Page 5 of 14
low-low
32•REF
2•REF
827.29412 964.58667 851.10588 987.41333 871.24706
786.28824
low-high
25.85294
41.00588
51.70588
62.40588
868.3
RF =
MHz
The
frequency is based on some assumptions. As
for example: the first IF and the image
frequencies should not be in a radio band
where strong interfering signals might occur
(because
receiving signals), the LO1 signal should be in
the range of 800 MHz to 930 MHz (because
this is the optimum frequency range of the
VCO1). Furthermore the first IF should be as
high as possible to achieve highest RF image
rejection.
high-high
30.14333
49.58667
60.28667
70.98667
1014.17
Evaluation Board Description
RF =
MHz
915
selection
(RF + IF2)/30
IF1 – LO2
LO1 – RF
high-low
32•REF
2•REF
they
787.21176
low-low
26.59706
63.89412
53.19412
42.49412
868/915MHz Receiver
RF =
MHz
915
of
could
EVB71112
the
high-low
30.85667
72.41333
61.71333
51.01333
1059.83
represent
RF =
MHz
915
reference
(RF + IF2)/34
EVB Description
LO2 – IF1
RF – LO1
low-high
32•REF
2•REF
827.49412
low-high
27.22647
43.75294
54.45294
65.15294
parasitic
RF =
MHz
April/08
915
crystal