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Электронный компонент: U4275B

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U4275B
TELEFUNKEN Semiconductors
Preliminary Information
1
Rev. A1: 14.03.1995
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 Interrupt output for abruptly occuring interferences
D Suitable for analogue as well as digital processing
D Mute function controllable by microcomputer
D Multipath noise cancellation
D Only a few external components necessary
Block diagram
Multipath
detector
Common
channel
detector
Interference
interrupt
Oscillator
Filter
Reset
Analogue
multiplex
Address
logic
MNC
control
Buffer
Bandgap
14
1
3
2
20
17
19
9
12
13
15
11
7
10
18
4
5
6
16
94 8644
FIL19
FIL26
CCHFIL
ADDR0
ADDR1
INT
OE
ANAOUT
V
S
MUTE
MPXIN
GND2
MPXOUT
GND1
MPFIL
CRIN
BFSOUT
AVFS
FSIN
Multipath
Noise
Cancellation
(Gain 1.5)
8
VREF
TELEFUNKEN Semiconductors
U4275B
Rev. A1: 14.03.1995
Preliminary Information
2
Pin description
Pin
Symbol
Function
1
FSIN
Fieldstrength input
2
BFSOUT
Buffered fieldstrength output
3
AVFS
Average of fieldstrength signal
4
MPXIN
Multiplex input signal
5
GND2
Analogue ground
6
MPXOUT Multiplex output signal
7
VS
Supply voltage
8
VREF
Reference voltage
9
INT
Interrupt output
10
MUTE
External mute input
11
ANAOUT Analogue multiplex output
12
ADDR0
Address 0 for analogue multi-
plexer
13
ADDR1
Address 1 for analogue multi-
plexer
14
CRIN
Ceramic resonator input
(456 kHz)
15
OE
Output enable for ANAOUT
16
GND1
Ground
17
CCFIL
Filter for common channel
detection
18
MPFIL
Filter for multipath detection
19
FIL26
Filter for 26 kHz detection
20
FIL19
Filter for 19 kHz-Pilot detection
1
2
3
4
5
6
7
8
10
9
19
18
17
16
14
15
13
12
11
20
FSIN
BFSOUT
AVFS
MPXIN
GND2
MPXOUT
VS
VREF
INT
MUTE
ANAOUT
ADDR0
ADDR1
CRIN
OE
GND1
CCFIL
MPFIL
FIL26
FIL19
94 8830
FSIN / BFSOUT
FSIN
40
mA
94 8647
V
S
BFSOUT
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.
AVFS
AVFS
40
mA
94 8648
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.
U4275B
TELEFUNKEN Semiconductors
Preliminary Information
3
Rev. A1: 14.03.1995
MPXIN / MPXOUT
94 8649
V
S
50 k
W
MPXIN
50 k
W
94 8650
V
S
60 k
W
60 k
W
MPXOUT
200
mA
V
S
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.
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.
MUTE
94 8651
MUTE
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
94 8652
CRIN
V
S
40 k
W
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
94 8653
ANAOUT
60
mA
+ 5 V
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.
TELEFUNKEN Semiconductors
U4275B
Rev. A1: 14.03.1995
Preliminary Information
4
INT
94 8654
25 k
W
+ 5 V
INT
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-
ms-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.
CCFIL
CCFIL
94 8655
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.
MPFIL
MPFIL
94 8656
100 k
W
100 nA
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
FIL19
94 8657
100 k
W
100 nA
FIL26
94 8658
100 k
W
100 nA
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
94 9669
V
S
30 k
30 k
VREF
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.
U4275B
TELEFUNKEN Semiconductors
Preliminary Information
5
Rev. A1: 14.03.1995
ADDR0 / ADDR1 / OE
OE
94 8662
20
mA
ADDR0
94 8659
20
mA
ADDR1
94 8660
20
mA
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
OE
ADDR1
ADDR0
ANAOUT
0
L
L
L
Internal reference voltage
Additional reset of the analog voltages for signal level, multipath,
common channel
1
L
L
H
Signal level
2
L
H
L
Multipath
3
L
H
H
Common channel
4
H
X
X
High impedance off-state