th71102 Melexis Company, th71102 Datasheet - Page 5

• Manufacturer Part Number: th71102
• Description: Receiver - 315/433mhz Fsk/ask, Double-conversion Superhet Lqfp32
• Manufacturer: Melexis Company

By configuring the TH71102 for double conversion and using its internal PLL synthesizer with fixed feedback
divider ratios of N1 = 8 (DIV_8) 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 315 MHz and
433.92 MHz RF reception at IF2 = 10.7 MHz. The columns in bold depict the selected frequency plans to
receive at 315 MHz and 433.92 MHz, respectively.
1.6.2
39010 71102
Rev. 014
IF1 image/MHz
RF image/MHz 380.54286 225.97778 429.45714 264.02222 533.44000 318.47112 582.35428 356.51556
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
REF
LO1
LO2
IF1
IF2
Selected Frequency Plans
Maximum Frequency Coverage
347.77143 270.48889 372.22857 289.51111 483.68000 376.19556 508.13714 395.21778
21.73571
32.77143
43.47143
54.17143
RF =
MHz
315
high-low
251.8
18.75
48.2
37.5
10.7
(RF – IF2)/14
300
f
min
high-high
LO2 – IF1
LO1 – RF
16•REF
16.90556
44.51111
33.81111
23.11111
2•REF
low-low
RF =
MHz
315
high-low
23.26429
57.22857
46.52857
35.82857
low-low
RF =
MHz
516.95
28.125
315
56.25
66.95
10.7
f
450
max
(RF – IF2)/18
IF1 – LO2
RF – LO1
Page 5 of 22
low-low
16•REF
2•REF
low-high
18.09444
25.48889
36.18889
46.88889
RF =
MHz
315
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 300 MHz to 450 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
30.23000
49.76000
60.46000
71.16000
433.92
RF =
MHz
selection
(RF + IF2)/14
IF1 – LO2
LO1 – RF
high-low
16•REF
2•REF
they
low-low
23.51222
57.72444
47.02444
36.32444
433.92
RF =
MHz
of
could
FSK/ASK Receiver
the
TH71102
high-low
31.75857
74.21714
63.51714
52.81717
433.92
represent
RF =
MHz
reference
315/433MHz
(RF + IF2)/18
LO2 – IF1
RF – LO1
low-high
16•REF
2•REF
Data Sheet
low-high
24.70111
38.70222
49.40222
60.10222
433.92
parasitic
RF =
MHz
April/08
crystal