EVB71112
868/915MHz Receiver
Evaluation Board Description
Features
!
!
!
!
!
!
Double-conversion superhet architecture for low high degree of image rejection
FSK for digital data and FM reception for analog signal transmission
FSK/FM demodulation with phase-coincidence demodulator
Low current consumption in active mode and very low standby current
Switchable LNA gain for improved dynamic range
RSSI allows signal strength indication and ASK detection
Ordering Information
Part No.
EVB71112-868-FSK-C
EVB71112-868-ASK-C
EVB71112-915-FSK-C
EVB71112-915-ASK-C
Application Examples
!
!
!
!
!
!
"
!
Tire Pressure Monitoring Systems (TPMS)
Remote Keyless Entry (RKE)
Wireless access control
Alarm and security systems
Garage door openers
Remote Controls
Home and building automation
Low-power telemetry systems
Evaluation Board
General Description
The TH71112 FSK/FM/ASK double-conversion superheterodyne receiver IC is designed for applications in
the European 868 MHz industrial-scientific-medical (ISM) band, according to the EN 300 220
telecommunications standard. It can also be used for any other system with carrier frequencies ranging from
750 MHz to 990 MHz (e.g. for applications to FCC part 15).
39012 71112 01
Rev. 011
Page 1 of 14
EVB Description
June/07
EVB71112
868/915MHz Receiver
Evaluation Board Description
Document Content
1
Theory of Operation ...................................................................................................3
1.1
1.2
1.3
1.4
1.5
1.6
1.6.1
1.6.2
General............................................................................................................................. 3
EVB Technical Data Overview ......................................................................................... 3
Block Diagram .................................................................................................................. 4
Mode Configurations ........................................................................................................ 4
LNA GAIN Control ............................................................................................................ 4
Frequency Planning.......................................................................................................... 4
Selected Frequency Plans........................................................................................................... 5
Maximum Frequency Coverage................................................................................................... 5
2
Application Circuits ...................................................................................................6
2.1
2.1.1
2.1.2
2.1.3
FSK Application Circuit..................................................................................................... 6
Circuit Diagram for FSK Reception.............................................................................................. 6
Board Component Values for FSK .............................................................................................. 7
Component Arrangement Top Side for FSK Reception .............................................................. 8
2.2
2.2.1
2.2.2
2.2.3
ASK Application Circuit..................................................................................................... 9
Circuit Diagram for ASK Reception ............................................................................................. 9
Board Component Values for ASK ............................................................................................ 10
Component Arrangement Top Side for ASK Reception ............................................................ 11
3
4
5
Evaluation Board Layouts .......................................................................................12
Board Variants..........................................................................................................12
Package Description ................................................................................................13
5.1
Soldering Information ..................................................................................................... 13
6
Disclaimer .................................................................................................................14
39012 71112 01
Rev. 011
Page 2 of 14
EVB Description
June/07
EVB71112
868/915MHz Receiver
Evaluation Board Description
1
1.1
Theory of Operation
General
With the TH71112 receiver chip, various circuit configurations can be arranged in order to meet a number of
different customer requirements. For FM/FSK reception the IF tank used in the phase coincidence
demodulator can also be constituted by a ceramic discriminator with a varactor diode to create an AFC
circuit. In ASK configuration, the RSSI signal is fed to an ASK detector, which is constituted by the
operational amplifier.
The superheterodyne configuration is double conversion where MIX1 and MIX2 are driven by the internal
local oscillator signals LO1 and LO2, respectively. This allows a high degree of image rejection, achieved in
conjunction with an RF front-end filter. Efficient RF front-end filtering is realized by using a SAW, ceramic or
helix filter in front of the LNA and by adding an LC filter at the LNA output.
A single-conversion variant, called TH71111, is also available. Both Receiver ICs have the same die. At the
TH71111 the second mixer MIX2 operates as an amplifier.
The TH71112 receiver IC consists of the following building blocks:
#
#
#
#
#
#
#
#
PLL synthesizer (PLL SYNTH) for generation of the first and second local oscillator signals LO1 and LO2,
parts of the PLL SYNTH are: the high-frequency VCO1, the feedback dividers DIV_16 and DIV_2,
a phase-frequency detector (PFD) with charge pump (CP) and a crystal-based reference oscillator (RO)
Low-noise amplifier (LNA) for high-sensitivity RF signal reception
First mixer (MIX1) for down-conversion of the RF signal to the first IF (IF1)
Second mixer (MIX2) for down-conversion of the IF1 to the second IF (IF2)
IF amplifier (IFA) to amplify and limit the IF2 signal and for RSSI generation
Phase coincidence demodulator (DEMOD) with third mixer (MIX3) to demodulate the IF signal
Operational amplifier (OA) for data slicing, filtering and ASK detection
Bias circuitry for bandgap biasing and circuit shutdown
1.2
EVB Technical Data Overview
!
Range of first IF2: 400 kHz to 22 MHz
!
Maximum input level: -10 dBm @ ASK
0 dBm @ FSK
!
Image rejection: > 60 dB (e.g. with 868.3 MHz
SAW front-end filter and at 10.7 MHz IF2)
!
Spurious emission: < -70 dBm
!
Input frequency acceptance range: up to
±100
kHz
!
RSSI range: 70 dB
!
FM/FSK deviation range:
±2.5
kHz to
±80
kHz
!
Maximum analog modulation frequency: 15 kHz
!
Input frequency range: 750 MHz to 990 MHz
!
Power supply range: 2.3 V to 5.5 V @ ASK
2.7 V to 5.5 V @ FSK
!
Temperature range: -40 °C to +85 °C
!
Standby current: 50 nA
!
Operating current: 7.5 mA @ low gain mode
9.2 mA @ high gain mode
!
Sensitivity: -109 dBm @ ASK 1)
-103 dBm @ FSK 2)
!
Range of first IF1: 10 MHz to 80 MHz
1) at 4 kbps NRZ, BER = 3⋅10
-3
, 180 kHz IF filter BW, incl. 3 dB SAW front-end-filter loss
2) at 4 kbps NRZ, BER = 3⋅10
-3
,
±
20 kHz FSK deviation, 180 kHz IF filter BW, incl. 3 dB SAW front-end-
filter loss
For more detailed information, please refer to the latest TH71112 data sheet revision
39012 71112 01
Rev. 011
Page 3 of 14
EVB Description
June/07
EVB71112
868/915MHz Receiver
Evaluation Board Description
1.3
Block Diagram
IN_MIX1
OUT_MIX2
FBC1
IF1N
VCC_MIX
VEE_LNAC
GAIN_LNA
OUT_LNA
VEE_MIX
OUT_IFA
IN_DEM
IF1P
VEE_IF
IN_IFA
2
3
4
5
6
7
8
9
RSSI
1
10
11
12
13
21
14
15
16
IN_LNA
31
MIX1
LNA
LO1
IF1
MIX2
IF2
LO2
MIX3
OUTP
OUTN
23
24
IFA
OAP
OA
DIV16
DIV2
PFD
RO
VCO1
VCC_LNA
VEE_LNA
20
OAN
19
OUT_OA
BIAS
VCC_BIAS
VEE_BIAS
VCC_PLL
VEE_RO
18
CP
ENRX
32
30
29
LF
26
RO
25
27
28
22
17
Fig. 1:
TH71112 block diagram
1.4
Mode Configurations
ENRX
0
1
Mode
RX standby
RX active
Description
RX disabled
RX enable
Note:
ENRX are pulled down internally
1.5
LNA GAIN Control
V
GAIN_LNA
< 0.8 V
> 1.4 V
Mode
HIGH GAIN
LOW GAIN
Description
LNA set to high gain
LNA set to low gain
Note:
hysteresis between gain modes to ensure stability
1.6
Frequency Planning
Frequency planning is straightforward for single-conversion applications because there is only one IF that
can be chosen, and then the only possible choice is low-side or high-side injection of the LO 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).
39012 71112 01
Rev. 011
Page 4 of 14
EVB Description
June/07
EVB71112
868/915MHz Receiver
Evaluation Board Description
By configuring the TH71112 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).
Injection type
REF
LO1
IF1
LO2
IF2
high-high
(RF – IF2)/30
32•REF
LO1 – RF
2•REF
LO2 – IF1
low-low
(RF – IF2)/34
32•REF
RF – LO1
2•REF
IF1 – LO2
high-low
(RF + IF2)/30
32•REF
LO1 – RF
2•REF
IF1 – LO2
low-high
(RF + IF2)/34
32•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 868.3 MHz and
915 MHz RF reception at IF2 = 10.7 MHz. The columns in bold depict the selected frequency plans to
receive at 868.3 MHz and 915 MHz, respectively.
RF =
868.3
MHz
28.58667
914.77333
46.47333
57.17333
Signal type
RF =
868.3
MHz
low-low
25.22353
807.15294
61.14706
50.44706
746.00588
39.74706
RF =
868.3
MHz
high-low
29.3
937.6
69.3
58.6
1006.9
47.9
RF =
868.3
MHz
low-high
25.85294
827.29412
41.00588
51.70588
786.28824
62.40588
RF =
915
MHz
high-high
30.14333
964.58667
49.58667
60.28667
1014.17
70.98667
RF =
915
MHz
low-low
26.59706
851.10588
63.89412
53.19412
787.21176
42.49412
RF =
915
MHz
high-low
30.85667
987.41333
72.41333
61.71333
1059.83
51.01333
RF =
915
MHz
low-high
27.22647
871.24706
43.75294
54.45294
827.49412
65.15294
Injection type high-high
REF / MHz
LO1 / MHz
IF1 / MHz
LO2 / MHz
RF image/MHz 961.24667
IF1 image/MHz
67.87333
1.6.2
Maximum Frequency Coverage
f
min
high-low
739.3
25.0
800
60.7
50.0
10.7
f
max
low-low
998.825
29.0625
930
68.825
58.125
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 800 MHz to 930 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
39012 71112 01
Rev. 011
Page 5 of 14
EVB Description
June/07
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