TH7111ENG Melexis Inc, TH7111ENG Datasheet - Page 4

• Manufacturer Part Number: TH7111ENG
• Description: IC RECEIVER FULL SIZE 44-LQFP
• Manufacturer: Melexis Inc

Specifications of TH7111ENG

• Rohs Status: RoHS non-compliant
• Frequency: 800MHz ~ 930MHz
• Sensitivity: -109dBm
• Data Rate - Maximum: 80 kbps
• Modulation Or Protocol: ASK, FM, FSK
• Applications: Alarm and Security Systems, RKE, TPMS
• Current - Receiving: 9.2mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 2.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-LQFP
• Features: -
• Memory Size: -
• Other names: TH7111

Frequency Planning
Frequency planning is straightforward for single-conversion applications because there is only one IF that
might be chosen, and then the only possible choice is low-side or high-side injection of the LO1 signal (which
is now the one and only LO signal in the receiver).
The receiver’s double-conversion architecture requires careful frequency planning. Besides the desired RF
input signal, there are a number of spurious signals that may cause an undesired response at the output.
Among them are the image of the RF signal (that must be suppressed by the RF front-end filter), spurious
signals injected to the first IF (IF1) and their images which could be mixed down to the same second IF (IF2)
as the desired RF signal (they must be suppressed by the LC filter at IF1 and/or by low-crosstalk design).
By configuring the TH7111 for double conversion and using its internal PLL synthesizer with fixed feedback
divider ratios of N1 = 16 (DIV_16) 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).
The following table depicts generated, desired, possible images and some undesired signals considering the
examples of 868.3 MHz and 915 MHz RF reception at IF2 = 10.7 MHz.
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 800 MHz
to 915 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. The columns in bold depict the selected frequency
plans to receive at 868.3 MHz and 915 MHz, respectively.
TH7111 Data Sheet
3901007111
Injection type
REF / MHz
LO1 / MHz
IF1 / MHz
LO2 / MHz
RF image/MHz 961.24667 746.00588
IF1 image/MHz
Signal type
Injection type
REF
LO1
LO2
IF1
IF2
868.3 MHz
914.77333 807.15294
28.58667
46.47333
57.17333
67.87333
high-high
RF =
(RF – IF2)/30
high-high
LO2 – IF1
LO1 – RF
868.3 MHz
32 REF
25.22353
61.14706
50.44706
39.74706
low-low
2 REF
RF =
868.3 MHz
high-low
1006.9
937.6
RF =
29.3
69.3
58.6
47.9
(RF – IF2)/34
IF1 – LO2
RF – LO1
low-low
32 REF
2 REF
868.3 MHz
Page 4 of 20
827.29412 964.58667 851.10588 987.41333 871.24706
786.28824
25.85294
41.00588
51.70588
62.40588
low-high
RF =
30.14333
49.58667
60.28667
70.98667
RF = 915
high-high
1014.17
MHz
(RF + IF2)/30
IF1 – LO2
LO1 – RF
high-low
32 REF
2 REF
787.21176
FSK/FM/ASK Receiver
RF = 915
26.59706
63.89412
53.19412
42.49412
low-low
MHz
RF = 915
30.85667
72.41333
61.71333
51.01333
high-low
1059.83
MHz
TH7111
868/915MHz
(RF + IF2)/34
LO2 – IF1
RF – LO1
low-high
32 REF
2 REF
827.49412
Nov. 2001
RF = 915
27.22647
43.75294
54.45294
65.15294
low-high
Rev. 005
MHz