EVB71102 Datasheet, PDF (5/14 Pages) Melexis Microelectronic Systems – 315/433MHz Receiver Evaluation Board Description

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
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.
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 high-low low-high high-high low-low high-low low-high
REF / MHz 21.73571 16.90556 23.26429 18.09444 30.23000 23.51222 31.75857 24.70111
LO1 / MHz 347.77143 270.48889 372.22857 289.51111 483.68000 376.19556 508.13714 395.21778
IF1 / MHz 32.77143 44.51111 57.22857 25.48889 49.76000 57.72444 74.21714 38.70222
LO2 / MHz 43.47143 33.81111 46.52857 36.18889 60.46000 47.02444 63.51714 49.40222
RF image/MHz 380.54286 225.97778 429.45714 264.02222 533.44000 318.47112 582.35428 356.51556
IF1 image/MHz 54.17143 23.11111 35.82857 46.88889 71.16000 36.32444 52.81717 60.10222
1.6.2 Maximum Frequency Coverage
Parameter
Injection type
RF / MHz
REF / MHz
LO1 / MHz
IF1 / MHz
LO2 / MHz
IF2/ MHz
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.
39012 71102 01
Rev. 011
Page 5 of 14
EVB Description
June/07