EVB71102
315/433MHz Receiver
Evaluation Board Description
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
high-high
(RF – IF2)/14
16•REF
low-low
(RF – IF2)/18
16•REF
high-low
(RF + IF2)/14
16•REF
low-high
(RF + IF2)/18
16•REF
REF
LO1
IF1
LO1 – RF
2•REF
RF – LO1
2•REF
LO1 – RF
2•REF
RF – LO1
2•REF
LO2
IF2
LO2 – IF1
IF1 – LO2
IF1 – LO2
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.
Signal type
RF =
315
MHz
RF =
315
MHz
RF =
315
MHz
RF =
315
MHz
RF =
433.92
MHz
RF =
433.92
MHz
RF =
433.92
MHz
RF =
433.92
MHz
Injection type high-high low-low
low-high high-high
high-low low-high
high-low
23.26429
372.22857
57.22857
46.52857
429.45714
35.82857
low-low
23.51222
376.19556
57.72444
47.02444
318.47112
36.32444
REF / MHz
LO1 / MHz
IF1 / MHz
LO2 / MHz
21.73571
16.90556
18.09444
30.23000
31.75857
24.70111
347.77143 270.48889
289.51111 483.68000
508.13714 395.21778
32.77143
43.47143
44.51111
33.81111
25.48889
36.18889
49.76000
60.46000
74.21714
63.51714
38.70222
49.40222
RF image/MHz 380.54286 225.97778
IF1 image/MHz 54.17143 23.11111
264.02222 533.44000
46.88889 71.16000
582.35428 356.51556
52.81717 60.10222
1.6.2
Maximum Frequency Coverage
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
fmin
high-low
251.8
18.75
300
fmax
low-low
516.95
28.125
450
RF / MHz
REF / MHz
LO1 / MHz
IF1 / MHz
LO2 / MHz
IF2/ MHz
48.2
66.95
56.25
10.7
37.5
10.7
39012 71102 01
Rev. 011
Page 5 of 14
EVB Description
June/07
MELEXIS [ Melexis Microelectronic Systems ]
