27MHZ to 67MHz Low-RF Single-Conversion Superhet Receiver DownloadLink 3797

Application Note
Receiver TH71102
Low RF
27MHz to 67MHz Low-RF Single-Conversion Superhet Receiver
1 The transformation of a high-RF double-conversion to a low-RF
single-conversion superhet receiver
Receiver ICs with fully integrated VCOs are very welcome to the system designer because there is no need
for external VCO components like varactor diodes or inductors. On the other hand, a fully integrated VCO
typically has a limited LO frequency range that restricts the receiver’s operating frequency range. The
frequency translation scheme of a standard double-conversion superhet (DCSH) receiver follows the rule
that the highest frequency of operation (high-RF) is down-converted by the first mixer to a lower frequency of
operation (low-RF) that constitutes the first IF. Then a second mixer handles the next step of downconversion to derive the second IF. It follows logically that the operating frequency range of a DCSH should
be down-scalable if the first mixer could be bypassed to make the second mixer’s input to be the terminal of
the desired signal frequency (now the low-RF). Then the DCSH is transformed to a single-conversion
superhet (SCSH) receiver.
The TH71102 block diagram, shown in Fig. 1, reveals that MIX1 ports IN_MIX1 and IF1 are fully accessible.
This gives the chance to connect the LNA output directly to the input of MIX2. In this situation, MIX2 is the
one and only mixer in the system, able to receive low-RF signals. Fig. 1 outlines how the transformation from
DCSH to SCSH can be realized by using the TH71102. As it can be seen from the block diagram, port LO1
of MIX1 cannot be disconnected because it is internal to the IC. Furthermore the internal signal path from
MIX1 to MIX2 is fixed. This implies to take care of two things:
The input of MIX1 must be AC-grounded to prevent from picking up unwanted high-RF signals that could
be down-converted and interfere with the desired low-RF
The output of MIX2 must be matched to the desired low-RF signal to keep parasitic LO1 feed-through as
low as possible.
Both demands can be easily met: first by applying a capacitor to pin IN_MIX1 that is well connected to
ground, while second comes along because the LC tank at pins IF1P and IF1N is trimmed to the desired lowRF anyway. The following table summarizes the relationships between the different frequencies in the SCSH
receiver chain.
Signal
low-side injection
high-side injection
REF (reference osc. freq.)
LO2
IF
(RF – IF)/2
2 • REF
RF – LO2
(RF + IF)/2
2 • REF
LO2 – RF
The specified LO1 frequency range of the TH71102 is 300 MHz to 450 MHz. This translates to an LO2 range
of 37.5 MHz to 56.25 MHz which is the new LO frequency range of the receiver that has been derived by
DCSH-to-SCSH transformation (LO2 of DCSH = LO of SCSH). The following table depicts the new operating
frequency range (RF desired), the reference (REF), and the LO and image frequency (RF image) of the
SCSH considering the example of an intermediate frequency of IF = 10.7 MHz.
Signal type
LO low-side injection
LO high-side injection
RF desired / MHz
REF / MHz
LO / MHz
RF image / MHz
48.2 to 66.95
18.75 to 28.125
37.5 to 56.25
26.8 to 45.55
26.8 to 45.55
18.75 to 28.125
37.5 to 56.25
48.2 to 66.95
390117110201
Rev. 002
Page 1 of 8
AN71102-Low RF
Jan./04
Application Note
Receiver TH71102
Low RF
According to CEPT/ERC recommendation 70-03, the following low-frequency services can be covered by the
modified TH71102 application circuit.
Service
Frequency range
Channel spacing
non-specific
SRDs
26.957 - 27.238 MHz
40.660 - 40.700 MHz
no channels
specified
model control
26.995 - 27.195 MHz
34.995 - 35.225 MHz
40.665 - 40.695 MHz
26.957 - 27.283 MHz
10 kHz
29.7 - 47.0 MHz
50 kHz
inductive
applications
narrow-band
audio
no channels
specified
Typical applications
telemetry, telecommand, alarms, data
in general and other similar
applications
controlling the movement of a model
car immobilizers, animal identification,
alarm systems, personal
identification, proximity
sensors, anti-theft systems,
automatic article identification
audio signal transmission
2 Measured data of the low-RF single-conversion superhet receiver
A test board has been setup to validate the theoretical approach of the DCSH-to-SCSH transformation. The
board’s circuit schematic corresponds to Fig. 2/3 with a receiving frequency of 40.68 MHz, the center
frequency of one of the non-specific SRD bands. The most important parameters are summarized in the
following table.
Vcc = 3.0 V, Ta = 23 °C, RF = 40.68 MHz, IF = 10.7 MHz, BIF = 150 kHz, ∆fFSK = ±30 kHz, MASK = 100 %,
data rate = 4 kbit/s NRZ, BER < 3⋅10-3
Parameter
Condition
Value
Unit
<100
nA
stand-by current
ENRX at 0 V
current consumption at LNA high gain
GAIN_LNA at 0 V
7.7
mA
current consumption at LNA low gain
GAIN_LNA open
6.3
mA
FSK input sensitivity at LNA high gain
GAIN_LNA at 0 V
-108
dBm
FSK input sensitivity at LNA low gain
GAIN_LNA open
-70
dBm
FSK maximum input signal at LNA high gain
GAIN_LNA at 0 V
-10
dBm
FSK maximum input signal at LNA low gain
GAIN_LNA open
0
dBm
ASK input sensitivity at LNA high gain
GAIN_LNA at 0 V
-110
dBm
ASK input sensitivity at LNA low gain
GAIN_LNA open
-72
dBm
ASK maximum input signal at LNA high gain
GAIN_LNA at 0 V
-24
dBm
ASK maximum input signal at LNA low gain
GAIN_LNA open
-5
dBm
image rejection
GAIN_LNA at 0 V
36
dB
rejection of undesired double-conversion RF at 451.72 MHz
GAIN_LNA at 0 V
77
dB
rejection of undesired double-conversion RF at 370.36 MHz
GAIN_LNA at 0 V
65
dB
spurious emission
GAIN_LNA at 0 V
< -104
dBm
390117110201
Rev. 002
Page 2 of 8
AN71102-Low RF
Jan./04
Application Note
Receiver TH71102
Low RF
3 Bock Diagram
FSK
output
18
OUT_OA
19
20
OAN
OAP
C14
17
22
OUT_IFA
C11
VEE_RO
25
13
C9
VCC
12
FBC1
C10
IF2
OUT_MIX2
C1
RO
CP
LF
C3
R1
PFD
29
IF1
6
IF1P
DIV2
51.38MHz
IF1N
L5
C8
L4
25.69MHz
LO2
MIX2
VCC_MIX
8
VCC
9
25.69 MHz
7
VCO1
4
IN_MIX1
DIV8
MIX1
5
VEE
CMIX1
VEE_LNA
LO1
loop filter
C7
411.04MHz
RF-filter
40.68 MHz
XTAL
26
VEE_IF
10
VEE
11
RO
IN_IFA
CERFIL
10.7 MHz
VCC
ENRX
VEE
VCC_PLL
27
21
IFA
RSSI
RSSI
ENRX
28
VCC
C16
14
15
C12
BIAS
CERRES
10.7 MHz
VEE_BIAS
MIX3
IN_DEM
16
C13
VEE
VCC_BIAS
CP
VCC
OA
24
23
OUTP
OUTN
C15
OUT_LNA
VCC
30
VCC_LNA
32
IN_LNA
2
390117110201
Rev. 002
1
VEE
Fig. 1
VEE_LNAC
VEE_LNA
LNA
GAIN_LNA
31
L3
VEE
3
C6
C5
C4
C0
RF Input
40.68 MHz
L2
TH71102 block diagram with external components for FSK reception
Page 3 of 8
AN71102-Low RF
Jan./04
Application Note
Receiver TH71102
Low RF
4 FSK Application Circuit
RSSI
C14
FSK output
C15 C16
C1
VCC
VCC
17
18
OAN 19
20
OAP
RSSI 21
OUT_OA
XTAL
25
VEE 22
VEE
OUTP 23
OUTN 24
VCC
CP
C13
IN_DEM 16
OUT_IFA 15
26
RO
27
VCC
28
ENRX
FBC2 13
29
LF
FBC1 12
30
VEE
VCC 14
C12
CERRES
VCC
C11
ENTRX
R1
C9
C3
C10
VEE
GAIN_LNA
OUT_LNA
IN_MIX1
VEE
IF1P
2
3
4
5
6
C5
1
C7
L3
C6
L4
CMIX1
VCC
32
CERFIL
9
OUT_MIX2
8
VCC
C4 VCC
VEE 10
IF1N
C0
L2
7
31 IN_LNA
50
C8
LCFIL
RF input
IN_IFA 11
L5
CB*
VCC
* each Vcc pin with blocking cap of 330pF
* one global Vcc blocking cap of 10nF
Fig. 2
390117110201
Rev. 002
Circuit diagram for FSK reception
Page 4 of 8
AN71102-Low RF
Jan./04
Application Note
Receiver TH71102
Low RF
4.1 Board Component Values for FSK (Fig. 2)
Part
Size
Value @
40.68 MHz
Tolerance
Description
C0
0805
100 pF
±10%
capacitor
C1
0805
15 pF
±10%
crystal series capacitor
C3
0805
1 nF
±10%
loop filter capacitor
C4
0603
120 pF
±5%
capacitor
C5
0603
100 pF
±5%
capacitor
C6
0603
150 pf
±5%
LNA output tank capacitor
C7
0603
22 pF
±5%
capacitor
CMIX1
0805
2.2nF
±10%
capacitor
C8
0603
68 pF
±5%
RF tank capacitor
C9
0805
33 nF
±10%
IFA feedback capacitor
C10
0603
1 nF
±10%
IFA feedback capacitor
C11
0603
1 nF
±10%
IFA feedback capacitor
C12
0603
1.5 pF
±5%
DEMOD phase-shift capacitor
C13
0603
680 pF
±10%
DEMOD coupling capacitor
C14
0805
10 – 47 pF
±5%
demodulator output low-pass capacitor, depending on data rate
C15
0805
10 – 47 pF
±5%
demodulator output low-pass capacitor, depending on data rate
RSSI output low-pass capacitor
C16
0603
1.5 nF
±10%
CP
0805
10 – 12 pF
±5%
CERRES parallel capacitor
R1
0805
±10%
loop filter resistor
L2
0603
10 kΩ
100 nH
±5%
inductor
L3
0603
100 nH
±5%
LNA output tank inductor
L4
0805
100 nH
±5%
RF tank inductor
L5
0805
100 nH
±5%
RF tank inductor
XTAL
HC49
SMD
CERFIL
SMD
type
±25ppm calibration
±30ppm temperature
SFECV10M7JA00
(SFECV10.7MJS)
@ BIF2 = 150 kHz, ±40kHz
CERRES
SMD
type
390117110201
Rev. 002
CDSCB10M7GA130
(CDACV10.7MG18)
fundamental-mode crystal, Cload = 10 pF to 15pF,
C0, max = 7 pF, Rm, max = 50 Ω
ceramic filter from Murata,
or equivalent part from different vendor
ceramic resonator from Murata,
or equivalent part from different vendor
Page 5 of 8
AN71102-Low RF
Jan./04
Application Note
Receiver TH71102
Low RF
5 ASK Application Circuit
RSSI
ASK output
R3
C13
C1
VCC
17
18
OAN 19
20
OAP
RSSI 21
VEE 22
25
OUT_OA
XTAL
OUTP 23
OUTN 24
VEE
VCC
VCC
C12
IN_DEM 16
OUT_IFA 15
26
RO
27
VCC
28
ENRX
FBC2 13
29
LF
FBC1 12
30
VEE
VCC 14
VCC
C11
ENTRX
R1
C9
C3
C10
VEE
GAIN_LNA
OUT_LNA
IN_MIX1
2
3
4
C5
1
C7
L3
C6
L4
CMIX1
VCC
IF1N
9
CERFIL
OUT_MIX2
8
7
IF1P
32
C4 VCC
6
VCC
C8
LCFIL
50
VEE 10
VEE
31 IN_LNA
C0
L2
5
RF input
IN_IFA 11
L5
CB*
VCC
* each Vcc pin with blocking cap of 330pF
* one global Vcc blocking cap of 10nF
Fig. 3
390117110201
Rev. 002
Circuit diagram for ASK reception
Page 6 of 8
AN71102-Low RF
Jan./04
Application Note
Receiver TH71102
Low RF
5.1 Board Component Values for ASK (Fig. 3)
Part
Size
Value @
40.68 MHz
Tolerance
C0
0805
100 pF
±10%
capacitor
C1
0805
15 pF
±10%
crystal series capacitor
C3
0805
1 nF
±10%
loop filter capacitor
C4
0603
120 pF
±5%
capacitor
C5
0603
100 pF
±5%
capacitor
C6
0603
150 pf
±5%
LNA output tank capacitor
C7
0603
22 pF
±5%
capacitor
CMIX1
0805
2.2nF
±10%
capacitor
C8
0805
68 pF
±5%
IF1 tank capacitor
C9
0805
33 nF
±10%
IFA feedback capacitor
C10
0603
1 nF
±10%
IFA feedback capacitor
C11
0603
1 nF
±10%
IFA feedback capacitor
C12
0805
1 nF to 100 nF
±10%
ASK data slicer capacitor, depending on data rate
C13
0603
1.5 nF
±10%
RSSI output low-pass capacitor
R1
0805
10 kΩ
±10%
loop filter resistor
R3
0603
±5%
ASK data slicer resistor, depending on data rate
L2
0603
100 kΩ
100 nH
±5%
inductor
L3
100 nH
±5%
LNA output tank inductor
L4
0603
0805
100 nH
±5%
RF tank inductor
L5
0805
100 nH
±5%
RF tank inductor
XTAL
HC49
SMD
CERFIL
SMD
type
±25ppm calibration
±30ppm temperature
SFECV10M7JA00
(SFECV10.7MJS)
@ BIF2 = 150 kHz, ±40kHz
390117110201
Rev. 002
Description
fundamental-mode crystal, Cload = 10 pF to 15pF,
C0, max = 7 pF, Rm, max = 50 Ω
ceramic filter from Murata,
or equivalent part from different vendor
Page 7 of 8
AN71102-Low RF
Jan./04
Application Note
Receiver TH71102
Low RF
Your Notes
For the latest version of this document. Go to our website at
www.melexis.com
Or for additional information contact Melexis Direct:
Europe and Japan:
All other locations:
Phone: +32 1367 0495
E-mail: [email protected]
Phone: +1 603 223 2362
E-mail: [email protected]
QS9000, VDA6.1 and ISO14001 Certified
390117110201
Rev. 002
Page 8 of 8
AN71102-Low RF
Jan./04
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