TH71102
315/433MHz
FSK/FM/ASK Receiver
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).
Injection type
REF
LO1
IF1
LO2
IF2
high-high
(RF – IF2)/14
16•REF
LO1 – RF
2•REF
LO2 – IF1
low-low
(RF – IF2)/18
16•REF
RF – LO1
2•REF
IF1 – LO2
high-low
(RF + IF2)/14
16•REF
LO1 – RF
2•REF
IF1 – LO2
low-high
(RF + IF2)/18
16•REF
RF – LO1
2•REF
LO2 – IF1
1.6.1
Selected Frequency Plans
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.
RF =
315
MHz
21.73571
347.77143
32.77143
43.47143
Signal type
RF =
315
MHz
low-low
16.90556
270.48889
44.51111
33.81111
225.97778
23.11111
RF =
315
MHz
high-low
23.26429
372.22857
57.22857
46.52857
429.45714
35.82857
RF =
315
MHz
low-high
18.09444
289.51111
25.48889
36.18889
264.02222
46.88889
RF =
433.92
MHz
high-high
30.23000
483.68000
49.76000
60.46000
533.44000
71.16000
RF =
433.92
MHz
low-low
23.51222
376.19556
57.72444
47.02444
318.47112
36.32444
RF =
433.92
MHz
high-low
31.75857
508.13714
74.21714
63.51714
582.35428
52.81717
RF =
433.92
MHz
low-high
24.70111
395.21778
38.70222
49.40222
356.51556
60.10222
Injection type high-high
REF / MHz
LO1 / MHz
IF1 / MHz
LO2 / MHz
RF image/MHz 380.54286
IF1 image/MHz
54.17143
1.6.2
Maximum Frequency Coverage
f
min
high-low
251.8
18.75
300
48.2
37.5
10.7
f
max
low-low
516.95
28.125
450
66.95
56.25
10.7
The selection of the reference crystal
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 they could represent parasitic
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.
Parameter
Injection type
RF / MHz
REF / MHz
LO1 / MHz
IF1 / MHz
LO2 / MHz
IF2/ MHz
39010 71102
Rev. 013
Page 5 of 22
Data Sheet
June/07
MELEXIS [ Melexis Microelectronic Systems ]
