TELEFUNKEN Semiconductors
U4275B
FM-Receiving Condition Analyser and Multipath Noise
Cancellation
Description
The U4275B is a bipolar integrated receiving conditions
analyser as well as multipath noise cancellation circuit.
It is designed for high performance car radio applications.
Features
D
Preparation of the fieldstrength signal
D
Detection of multipath and common channel
interferences
D
Evaluation of the receiving conditions by
microcomputer
D
D
D
D
D
Interrupt output for abruptly occuring interferences
Suitable for analogue as well as digital processing
Mute function controllable by microcomputer
Multipath noise cancellation
Only a few external components necessary
Block diagram
FIL19
20
CRIN
14
Oscillator
Common
channel
detector
Filter
Interference
interrupt
9
INT
FIL26
19
CCHFIL
17
12
Reset
Address
logic
1
FSIN
AVFS
3
Multipath
detector
Analogue
multiplex
11
13
15
ADDR0
ADDR1
OE
ANAOUT
2
BFSOUT
Buffer
MNC
control
Multipath
Noise
Cancellation
(Gain 1.5)
18
4
5
6
8
Bandgap
7
V
S
10
94 8644
16
GND1
MUTE MPFIL
GND2
VREF
MPXIN MPXOUT
Rev. A1: 14.03.1995
Preliminary Information
1
U4275B
Pin description
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Symbol
FSIN
BFSOUT
AVFS
MPXIN
GND2
MPXOUT
VS
VREF
INT
MUTE
ANAOUT
ADDR0
ADDR1
CRIN
OE
GND1
CCFIL
MPFIL
FIL26
FIL19
Function
Fieldstrength input
Buffered fieldstrength output
Average of fieldstrength signal
Multiplex input signal
Analogue ground
Multiplex output signal
Supply voltage
Reference voltage
Interrupt output
External mute input
Analogue multiplex output
Address 0 for analogue multi-
plexer
Address 1 for analogue multi-
plexer
Ceramic resonator input
(456 kHz)
Output enable for ANAOUT
Ground
Filter for common channel
detection
Filter for multipath detection
Filter for 26 kHz detection
Filter for 19 kHz-Pilot detection
TELEFUNKEN Semiconductors
FSIN 1
BFSOUT 2
AVFS 3
MPXIN 4
GND2 5
MPXOUT 6
VS
7
20 FIL19
19 FIL26
18 MPFIL
17 CCFIL
16 GND1
15 OE
14 CRIN
13 ADDR1
12 ADDR0
11 ANAOUT
94 8830
VREF 8
INT
9
MUTE 10
FSIN / BFSOUT
V
S
40
m
A
FSIN
94 8647
AVFS
BFSOUT
AVFS
40
m
A
94 8648
All information about reception conditions is derived
from the fieldstrength voltage. The fieldstrength voltage
at FSIN is initially buffered so as not to impair the
characteristics of the IF IC and is available at BFSOUT.
The fieldstrength signal at buffer output BFSOUT is
averaged over time and applied to input AVFS via an RC
low-pass filter with a large time constant.
2
Preliminary Information
Rev. A1: 14.03.1995
TELEFUNKEN Semiconductors
MPXIN / MPXOUT
V
S
50 k
W
MPXIN
50 k
W
94 8649
U4275B
The function unit MNC can be controlled externally via
this pin. Blanking occurs when the voltage at the MUTE
pin falls below 1 V. A voltage in the range VS/2 > 1 V
defines the switching threshold as from which multipath
interference is signalled at pin INT.
CRIN
V
S
V
S
60 k
W
MPXOUT
60 k
W
94 8650
V
S
CRIN
40 k
W
200
m
A
94 8652
The MPX signal is fed directly from the FM demodulator
to input MPXIN and is available amplified by a factor of
1.5 at MPXOUT. The MPX signal is blanked out in the
event of multipath interference or when MUTE is
activated externally in the circuit part MNC (Multipath
Noise Canceller). In all other cases, the MPX signal
passes through the IC unchanged.
The internal one-pin oscillator is connected to CRIN with
a 456 kHz ceramic resonator. The 456 kHz reference
frequency is used for calibrating the filters and generating
pulses at INT.
ANAOUT
+5V
GND2
GND2 is the reference potential for the MPX signal.
GND2 should be connected directly with the ground
terminal of the IF FM demodulator to ensure a high
signal-to-noise ratio of the MPX signal.
ANAOUT
60
m
A
94 8653
MUTE
Analyzer output. DC values are available at this pin that
characterize the respective reception situation. The
output voltage is limited to max. 5 V. ANAOUT is a
multiplex output, i.e. the value for the fieldstrength, level
of multipath interference or level of common channel
interference is applied to this output depending on
addressing. ANAOUT can be switched to the
high-impedance state by means of OE.
MUTE
94 8651
Rev. A1: 14.03.1995
Preliminary Information
3
U4275B
INT
+5V
25 k
W
INT
TELEFUNKEN Semiconductors
The controller element detects the absolute value of
occuring multipath interference. This information is
stored in a capacitor which must be connected externally
to MPFIL. The capacitor voltage can be interrogated by
the system controller via ANAOUT.
FIL19 / FIL26
94 8654
Certain types of abruptly occuring interference with
reception require a fast reaction by the receiver. INT
signals such events to other circuit parts by means of
40-
m
s-wide pulses (low active). The output voltage is
limited to 5 V to permit direct activation of a system
controller. A monoblend function can thus be activated on
simple receivers. On antenna-diversity receivers, INT
can activate switchover between antennas.
FIL19
100 k
W
100 nA
94 8657
CCFIL
FIL26
CCFIL
100 k
W
100 nA
94 8655
94 8658
100 k
W
100 nA
The controller element detects the absolute value of
occuring common channel interference. This information
is stored in a capacitor which must be connected
externally to CGFIL. The capacitor voltage can be
selected by the system controller and then available via
ANAOUT.
In order to differentiate the various types of interference,
the amplitudes of a few spectral components of the
fieldstrength signal are determined and filtered in FIL19
and FIL26 for further processing.
VREF
V
S
30 k
VREF
30 k
MPFIL
MPFIL
100 k
W
94 9669
100 nA
94 8656
IF Mute is activated, the reference voltage VREF will
apply to the output MPXOUT. A capacitor of 100 nF
should be connected at VREF for filtering.
4
Preliminary Information
Rev. A1: 14.03.1995
TELEFUNKEN Semiconductors
U4275B
ADDR0 / ADDR1 / OE
20
m
A
ADDR0
94 8659
20
m
A
20
m
A
ADDR1
94 8660
OE
94 8662
The desired output variable at ANAOUT is selected via the address lines ADDR0 and ADDR1 and switched to the
output via the enable input OE. The following assignment applies:
No
0
OE
L
ADDR1
L
ADDR0
L
ANAOUT
Internal reference voltage
Additional reset of the analog voltages for signal level, multipath,
common channel
Signal level
Multipath
Common channel
High impedance off-state
1
2
3
4
L
L
L
H
L
H
H
X
H
L
H
X
Rev. A1: 14.03.1995
Preliminary Information
5
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