th71101 Melexis Company, th71101 Datasheet - Page 5

• Manufacturer Part Number: th71101
• Description: Receiver - 315/433mhz Fsk/ask, Single-conversion Superhet Lqfp32
• Manufacturer: Melexis Company

By using the internal PLL synthesizer of the TH71101 with the fixed feedback divider ratio of N = 16
(DIV_16), two types of down-conversion are possible: low-side injection of LO and high-side injection of LO.
The following table summarizes some equations that are useful to calculate the crystal reference frequency
(REF) and the LO frequency, for a given RF and IF.
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 IF = 10.7 MHz.
The selection of the reference crystal frequency is based on some assumptions. As for example: the image
frequency should not be in a radio band where strong interfering signals might occur (because they could
represent parasitic receiving signals), the LO signal should be in the range of 300 MHz to 450 MHz (because
this is the optimum frequency range of the VCO1). Furthermore the IF should be as high as possible to
achieve highest RF image rejection. The columns in bold depict the selected frequency plans to receive at
315 MHz and 433.92 MHz, respectively.
1.6.2
39010 71101
Rev. 015
RF image / MHz
Injection type
Signal type
REF / MHz
LO / MHz
Selected Frequency Plans
Maximum Frequency Coverage
Injection type
Injection type
Parameter
REF / MHz
RF image
RF / MHz
LO / MHz
IF/ MHz
REF
LO
IF
RF = 315 MHz
19.01875
304.3
293.6
low
RF = 315 MHz
(RF – IF)/16
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16 • REF
20.35625
RF – 2IF
RF – LO
325.7
336.4
289.3
18.75
high
10.7
high
low
300
f
min
RF = 433.92 MHz
26.45125
423.22
412.52
low
FSK/ASK Receiver
(RF + IF)/16
16 • REF
RF + 2IF
LO – RF
TH71101
28.125
460.7
high
10.7
f
450
RF = 433.92 MHz
low
max
315/433MHz
27.78875
444.62
455.32
high
Data Sheet
April/08