EVB71111
868/915MHz Receiver
Evaluation Board Description
Features
!
!
!
!
!
!
Single-conversion superhet architecture for low external component count
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.
EVB71111-868-FSK-C
EVB71111-868-ASK-C
EVB71111-915-FSK-C
EVB71111-915-ASK-C
Application Examples
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!
!
!
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"
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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 TH71111 FSK/FM/ASK single-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
800 MHz to 930 MHz (e.g. for applications to FCC part 15).
39012 71111 01
Rev. 011
Page 1 of 14
EVB Description
June/07
EVB71111
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 71111 01
Rev. 011
Page 2 of 14
EVB Description
June/07
EVB71111
868/915MHz Receiver
Evaluation Board Description
1
1.1
Theory of Operation
General
With the TH71111 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.
A double-conversion variant, called TH71112, is also available. This receiver IC allows a higher degree of
image rejection, achieved in conjunction with an RF front-end filter. Both RXICs have the same die. At the
TH71112, the second mixer (MIX2) is used to down-convert the first IF (IF1) to the second IF (IF2). At the
TH71111, MIX2 operates as an amplifier.
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.
The TH71111 receiver IC consists of the following building blocks:
#
#
#
#
#
#
#
#
PLL synthesizer (PLL SYNTH) for generation of the local oscillator signal LO, parts of the PLL SYNTH
are: the high-frequency VCO1, the feedback divider DIV_32, 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 IF
IF pre amplifier which is a mixer cell (MIX2) that operates as an amplifier
IF amplifier (IFA) to amplify and limit the IF 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
!
Maximum input level: -10 dBm @ ASK
0 dBm @ FSK
!
Image rejection: > 45 dB (e.g. with 868.3 MHz
SAW front-end filter and at 10.7 MHz IF)
!
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: 800 MHz to 930 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 IF: 400 kHz to 22 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 TH71111 data sheet revision
39012 71111 01
Rev. 011
Page 3 of 14
EVB Description
June/07
EVB71111
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
LO
IF
MIX2
IF
MIX3
OUTP
OUTN
23
24
IFA
OAP
OA
20
OAN
19
DIV_32
PFD
RO
OUT_OA
BIAS
VCC_BIAS
VEE_BIAS
VCC_PLL
VEE_RO
18
VCO1
VCC_LNA
VEE_LNA
CP
ENRX
32
30
29
LF
26
RO
25
27
28
22
17
Fig. 1:
TH71111 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 single-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 is the image of the RF signal that must be suppressed by the RF front-end filter.
39012 71111 01
Rev. 011
Page 4 of 14
EVB Description
June/07
EVB71111
868/915MHz Receiver
Evaluation Board Description
By using the internal PLL synthesizer of the TH71111 with the fixed feedback divider ratio of N = 16
(DIV_32), 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.
Injection type
REF
LO
IF
RF image
low
(RF – IF)/32
32
•
REF
RF – LO
RF – 2IF
high
(RF + IF)/32
32
•
REF
LO – RF
RF + 2IF
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 IF = 10.7 MHz.
Signal type
Injection type
REF / MHz
LO / MHz
RF image / MHz
RF = 868.3 MHz
low
26.80000
857.6
846.9
RF = 868.3 MHz
high
27.46875
879.0
889.7
RF = 915 MHz
low
28.25938
904.3
893.6
RF = 915 MHz
high
28.92813
925.7
936.4
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 800 MHz to 930 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
868.3 MHz and 915 MHz, respectively.
1.6.2
Maximum Frequency Coverage
Parameter
Injection type
RF / MHz
REF / MHz
LO / MHz
IF/ MHz
f
min
high
789.3
25.0
800
10.7
f
max
low
940.7
29.0625
930
10.7
39012 71111 01
Rev. 011
Page 5 of 14
EVB Description
June/07
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