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Features
* * * * * * * *
Preparation of the fieldstrength signal Detection of multipath and common channel interferences Evaluation of the receiving conditions by microcomputer Interrupt output for abruptly occuring interferences Suitable for analog as well as digital processing Mute function controllable by microcomputer Multipath noise cancellation Only few external components necessary
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.
Block Diagram
Figure 1.
FIL19 20 14 CRIN Oscillator Common channel detector Filter Interference interrupt 9 INT FIL26 19 CCHFIL 17
FM Receiving Condition Analyzer and Multipath Noise Cancellation IC U4275B
12 Reset Address logic 1 FSIN 3 AVFS 2 BFSOUT Buffer Multipath Noise
Cancellation (Gain 1.5)
ADDR0 ADDR1 OE
13 15
Multipath detector
Analogue multiplex 11 ANAOUT
MNC control
7 Bandgap VS
10
18
4
5
6
8
16 GND1
MUTE MPFIL
GND2 VREF MPXOUT MPXIN
Ordering Information
Extended Type Number U4275B-MFL U4275B-MFLG3 Package SO20 plastic SO20 plastic Taped and reeled Remarks
Rev. A3, 16-Oct-01
1 (14)
Pin Configuration
Figure 2. Pinning SO20
FSIN BFSOUT AVFS MPXIN GND2 MPXOUT VS VREF INT 1 2 3 4 5 6 7 8 9 20 FIL19 19 FIL26 18 MPFIL 17 CCFIL 16 GND1 15 OE 14 CRIN 13 ADDR1 12 ADDR0 11 ANAOUT
MUTE 10
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 Fieldstrength input Buffered fieldstrength output Average of fieldstrength signal Multiplex input signal Analog ground Multiplex output signal Supply voltage Reference voltage Interrupt output External mute input Analog multiplex output Address 0 for analog multiplexer Address 1 for analog multiplexer 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 Function
2 (14)
U4275B
Rev. A3, 16-Oct-01
U4275B
FSIN / 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.
VS
40 A FSIN
BFSOUT
AVFS
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.
40 A
AVFS
MPXIN / MPXOUT
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.
VS 50 k MPXIN
VS 60 k MPXOUT 60 k
VS
50 k
200 A
3 (14)
Rev. A3, 16-Oct-01
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. 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.
MUTE
MUTE
CRIN
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.
VS
CRIN
40 k
ANAOUT
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.
+5V
ANAOUT
60 A
4 (14)
U4275B
Rev. A3, 16-Oct-01
U4275B
INT
Certain types of abruptly occuring interferences with reception require a fast reaction by the receiver. INT signals such events to other circuit parts by means of 40-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.
+5V 25 k INT
CCFIL
This 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 which is then available via ANAOUT.
CCFIL
100 k
100 nA
MPFIL
This 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.
MPFIL
100 k
100 nA
5 (14)
Rev. A3, 16-Oct-01
FIL19 / FIL26
In order to differentiate the various types of interferences, the amplitudes of a few spectral components of the fieldstrength signal are determined and filtered in FIL19 and FIL26 for further processing.
FIL19
100 k
FIL26
100 k
100 nA
100 nA
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.
VS 30 k VREF
30 k
ADDR0 / ADDR1 / OE
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. For assignment, see table next page.
20 A
20 A
20 A
ADDR0
ADDR1
OE
6 (14)
U4275B
Rev. A3, 16-Oct-01
U4275B
No
OE
ADDR1
ADDR0
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
0
L
L
L
1 2 3 4
L L L H
L H H X
H L H X
Functional Description
Interference with FM reception can be triggered by various causes, such as multipath reception, adjacent and insufficient field strength. At the same time, multipath reception is responsible for the most frequently occurring types of interference. In order to suppress this interference systematically, it is first necessary to analyze the received signal so that it is possible to derive the type of interference at any time. The circuit U4275B analyzes the FM reception conditions and makes the data available. This data can be requested by a system controller and evaluated (see figure 1). It is thus possible to introduce measures for optimizing reception - possibly tailored to individual types of interference. Acoustically relevant multipath interference, since it requires a short reaction time, is suppressed directly by the circuit via a Multipath Noise Cancellation (MNC) function. The U4275B can be used both in conventional receivers and in receivers with digital signal processing. Furthermore, it is designed so that it can activate switchover between antennas on antenna-diversity receivers. The integrated circuit can be connected in cascade without much wiring for tuner-diversity receivers. The field strength voltage of the IF amplifier provides all the information about the reception conditions. The following demands are placed on the field strength output of the IF amplifier: 1. A linear characteristic, i.e. the output voltage must be proportional to the logarithm of the IF voltage in the range of RF levels encountered in practice. Deviations from linearity lead to a different evaluation of interference signals of the same intensity of the signal levels are different. 2. The "signal level" output has to react to extremely fast dips in the field strength. Total field strength failures lasting 500 ns and occuring a voltage dip to approx. 0 V at the field strength output.
Restrictions
The field strength voltage becomes increasingly noisy in the range of low RF levels (< 30 dBV). The noise prevents reliable detection of interference. Therefore, only the average field strength value can be evaluated over a relatively large time constant in this range. The pilot signal component in the receive signal is an important basis for quality assessment. Multipath detection and common channel detection therefore function only in the case of stereo transmitters.
7 (14)
Rev. A3, 16-Oct-01
Figure 3. System block diagram
MPX in FM - tuner
Fieldstrength signal Address MPX out AFleft
U4275B
Interrupt output ANA out
Digital or analog signal processing
AFright
System controller
Multipath Detector
Typical multipath interference is characterized by fast, modulation-dependent field strength dips, as shown in figure 2. The multipath detector detects these field strength dips and evaluates them in accordance with the level of anticipated acoustic interference. In the case of acoustically relevant interference, it operates the interrupt output INT and the MNC function as a reaction to the interference. If the acoustic effects of interference can be reduced by monoblend, only pulses will appear at output INT. In the case of stronger interference, interference suppression takes place by means of the Multipath Noise Cancellation (MNC) function. The multipath interference also generates a voltage proportional to the interference level at MPFIL. The capacitor connected there is responsible for storing the information to give the system controller sufficient time to read out the value at ANAOUT. The capacitor at MPFIL is discharged again slowly with a long time constant. The corresponding addressing at ADDR0, ADDR1 and OE to permit a rapid assessment when the station is changed.
Multipath Noise Cancellation (MNC)
Extremely strong multipath interference remains audible in spite of the monoblend function. The remaining interference is reduced still further by the MNC circuit if the output MPXOUT is connected to a reference voltage for a few microseconds while the interference is still occuring. In order to eliminate the possibility of malfunctions, activation of the MNC depends on the following conditions: * * The average field strength must exceed a certain value so that the noise in the field strength signal does not cause the MNC to respond at low RF voltages and the field strength dip must not be caused by adjacent-channel interference. Blanking will otherwise make the modulation of the adjacent channel audibly. The information for this purpose is derived from the common channel detector.
The MNC function can also be activated externally via the MUTE pin (low active). The circuit can therefore also be used as a fast high performance mute stage.
Common Channel Detector
The common channel detector evaluates the spectral composition of the field strength signal to distinguish common channel interference from other types of interference. This is a particularly difficult task, since weak multipath interference results in a spectrum of the field strength signal that is similar to that of common channel interference. the pilot signal portion of the field strength signal serves as a reference variable to permit a clear distinction to be made. A voltage proportional to the interference is generated at the filter
8 (14)
U4275B
Rev. A3, 16-Oct-01
U4275B
input CCFIL in the case of common channel interference. The external capacitor is responsible for storing the information to give the system controller sufficient time to read out the value at ANAOUT. The capacitor is discharged again slowly at CCFIL, with a long time constant. The capacitor can also be discharged rapidly via corresponding addressment when stations are changed. The common channel detector is blocked for further 20 ms after the detectors are reset to prevent transitory phenomena in the selective filters from causing an indicating error. Figure 4.
Absolute Maximum Ratings
Reference point Pin1b, unless otherwise specified
Parameter Supply voltage Supply current ...... .......Pin 7 ...... .......Pin 7 Symbol VS IS Tamb Tstg Tj VESD Value 10 t.b.d. -30 to +85 t.b.d. t.b.d. 2000 Unit V mA C C C V
Ambient temperature range Storage temperature range Junction temperature Electrostatic handling (MIL standard 883 C)
Thermal Resistance
Parameter Junction ambient Symbol RthJA Value t.b.d. Unit K/W
9 (14)
Rev. A3, 16-Oct-01
Electrical Characteristics
Tamb = 25C, VS = 8.5 V, unless otherwise specified
No. Parameters Supply voltage Supply current Fieldstrength Input voltage Output voltage Bandwidth Input voltage Multipath noise cancellation MPX input voltage MPX output voltage THD Bandwidth Noise figure Mute depth Gain Address logic Input voltage High Low Input current Interrupt output INT Output voltage Reference voltage VREF Output voltage Analog multiplex output Output voltage Oscillator Input voltage Mute Input voltage Low High 10 10 VMUTE VMUTE 0 3 1 VS V V 14 VOSC 50
mVRMS
Test Conditions
Pin 7 7 1
Symbol VS IS Vi Vout BW V VMPXIN VMPXOUT
Min. 8 6 0 50 100 0
Typ. 8.5 8
Max. 10 10 5.0 5000 5 350 525
Unit V mA V mV kHz V VRMS VRMS % kHz
Type*
Rload / Cload
2 2 3 4
RL = 10 k RL = 10 k VMPXIN = 350 mV RL = 10 k RL = 10 k RL = 10 k
6 6 6 6 6 12, 13, 15 13, 13, 15 12 12 9 9 8
0.06 100 75 G VIN VIN IIN IIN VINT VINT VREF VANA 0.200 0 4.75 VS/2 0 3 82 3.5
0.2
dB dB 1 VS 1 0.5 0.3 5.25 V V A A V V V 5.2 V
Low High Low, RL = High RL =
RL = 10 k
11
*) Type means: A =100% tested, B = 100% correlation tested, C = Characterized on samples, D = Design parameter
10 (14)
U4275B
Rev. A3, 16-Oct-01
U4275B
Application Circuit
Figure 5.
560 k 150 nF
560 k
560 k 150 nF 150 nF
20 14 Oscillator 456 kHz
19
17 9 Control signal 12 13 Reset Address logic
Common channel detector Filter
Interference interrupt
15
Fieldstrength 1 3 47 k 2 100 nF 10 Mute control FM - tuner 560 k 150 nF 18 Buffer MNC control Multipath Noise Multipath detector Analogue multiplex
11 Exception quality Supply voltage
7 Bandgap
Cancellation (Gain 1.5)
4 5 6 8
16 100 nF
MPX - Decoder & audio MPX
MPX
1 F
System - controller
11 (14)
Rev. A3, 16-Oct-01
Package Information
Package SO20
Dimensions in mm
12.95 12.70 9.15 8.65 7.5 7.3
2.35 0.25 10.50 10.20 11
0.4 1.27 11.43 20
0.25 0.10
technical drawings according to DIN specifications
1
10
12 (14)
U4275B
Rev. A3, 16-Oct-01
U4275B
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13 (14)
Rev. A3, 16-Oct-01
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(c) Atmel Germany GmbH 2001. Atmel Germany GmbH makes no warranty for the use of its products, other than those expressly contained in the Company's standard warranty which is detailed in Atmel Germany GmbH's Terms and Conditions. The Company assumes no responsibility for any errors which may appear in this document, reserves the right to change devices or specifications detailed herein at any time without notice, and does not make any commitment to update the information contained herein. No licenses to patents or other intellectual property of Atmel Germany GmbH are granted by the Company in connection with the sale of Atmel Germany GmbH products, expressly or by implication. Atmel Germany GmbH's products are not authorized for use as critical components in life support devices or systems. Data sheets can also be retrieved fron the Internet: http://www.atmel-wm.com
Rev. A3, 16-Oct-01

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