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U4276B
FM Multipath Noise Cancellation
Description
The U4276B is a bipolar integrated multipath noise cancellation circuit. It is designed for high performance car radio applications.
Features
D Preparation of the fieldstrength signal D Multipath noise cancellation
D Mute function controllable by microcomputer D Suitable for analogue as well as digital processing D Only a few external components necessary
Block Diagram
BFSOUT 7 2 FSIN Buffer Bandgap VS 6 3 GND
1 AVFS 4 MPXIN
Multipath detection
Multipath noise cancellation 8
5 MPXOUT
95 10619
MUTE
Pin Description
Pin 1 2 3 4 5 6 7 8 Symbol AVFS FSIN GND MPXIN MPXOUT VS BFSOUT MUTE Function Average of fieldstrength signal Fieldstrength input Ground Multiplex input signal Multiplex output signal Supply voltage Buffered fieldstrength output External mute input AVFS 1 FSIN 2 GND 3 MPXIN 4
95 10632
8 MUTE 7 BFSOUT 6 VS 5 MPXOUT
TELEFUNKEN Semiconductors Rev. A1, 05-Sep-96
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Preliminary Information
U4276B
FSIN / BFSOUT
VS 40 mA FSIN
94 8647
MPXIN / MPXOUT
VS 50 kW MPXIN
BFSOUT
50 kW
94 8649
All information about reception conditions is derived from the fieldstrength signal. The fieldstrength signal at FSIN is initially buffered so as not to impair the characteristics of the IF IC and is available at BFSOUT.
VS 60 kW
VS
AVFS
MPXOUT 60 kW 200 mA
40 mA
94 8650
AVFS
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.
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.
MUTE
MUTE
94 8651
The function unit MNC can be controlled externally via this pin. Blanking occurs when the voltage at the MUTE pin falls below 1 V.
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Preliminary Information
TELEFUNKEN Semiconductors Rev. A1, 05-Sep-96
U4276B
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. 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 U4276B can be used both in conventional receivers and in receivers with digital signal processing. 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 dBmV). 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.
MPX in FM - tuner
Fieldstrength signal Mute MPX out
AFleft
U4276B
Digital or analogue signal processing
AFright
System controller
95 10633
Figure 1. Block diagram
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 muted for a few microseconds while the interference is still occuring (figure 2). In order to eliminate the possibility of malfunctions, activation of the MNC depends on the following condition: - 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 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.
TELEFUNKEN Semiconductors Rev. A1, 05-Sep-96
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Preliminary Information
U4276B
94 8663
Figure 2.
In order to achieve best performance, the MNC-circuit has to be adapted well to the fieldstrength output of the IF-IC. This can be done by adjustment of the DC-level at
Pin Mute (R2/R3, see figure 4) in the range of V/2 The principle behaviour is shown in figure 3.
" 1 V.
95 10694
Field strength
V Mute
+V 2
S
V Mute
tV 2
S
V Mute 1.17 V
uV 2
S
MNC activation level (AVFS)
30
Figure 3.
RF level (dBmV)
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Preliminary Information
TELEFUNKEN Semiconductors Rev. A1, 05-Sep-96
U4276B
95 10695
VS R2 Mute R3
Figure 4.
Absolute Maximum Ratings
Reference point Pin 1b, unless otherwise specified Parameters Supply voltage Pin 6 Supply current Pin 6 Ambient temperature range Storage temperature range Junction temperature Electrostatic handling (MIL standard 883 C) Symbol VS IS Tamb Tstg Tj VESD Value 10 t.b.d. - 30 to + 85 -55 to +150 125 2000 Unit V mA C C C V
"
Thermal Resistance
Parameters Junction ambient Symbol RthJA Maximum t.b.d. Unit K/W
Electrical Characteristics
Tamb = 25_C, VS = 8.5 V, unless otherwise specified Parameters Supply voltage Supply current Fieldstrength Input voltage Output voltage Bandwidth Input voltage Test conditions / Pins Pin 6 Pin 6 Pin 2 Pin 7 Pin 7 Pin 1 Symbol VS IS Vi Vout BW V Min. 8 2 0 50 100 0 Typ. 8.5 3 Max. 10 5 5.0 5000 Unit V mA V mV KHz V
Rload Cload
5
TELEFUNKEN Semiconductors Rev. A1, 05-Sep-96
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Preliminary Information
U4276B
Parameters Test conditions / Pins Multipath Noise Cancellation MPX input voltage Pin 4 MPX output voltage RL = 10 kW Pin 5 THD RL = 10 kW Pin 5 VMPXIN = 350 mV Bandwidth RL = 10 kW Pin 5 Mute-depth RL = 10 kW Pin 5 Gain RL = 10 kW Pin 5 Mute Input voltage Pin 8 low high Symbol VMPXIN VMPXOUT 0.06 300 75 G VMUTE 0 3 1 VS V Min. Typ. Max. 350 525 0.2 Unit VRMS VRMS % kHz dB dB
82 3.5
Application Circuit
VS R1 100 4.7 mF C3 6 3 Buffer R4 47 k Multipath detection Multipath noise cancellation 8
95 10620
BFSOUT 7 FSIN 2 Bandgap R2 GND 56 k
5
MPXOUT
AVFS C2 680 nF MPXIN
1 4
MUTE R3 56 k
mC
100 nF
C1
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Preliminary Information
TELEFUNKEN Semiconductors Rev. A1, 05-Sep-96
U4276B
Ordering Information
Extended type number U4276B-AFP U4276B-AFPG3 Package SO8 plastic SO8 plastic Remarks Taping according to IEC-286-3
Dimensions in mm
94 8862
TELEFUNKEN Semiconductors Rev. A1, 05-Sep-96
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Preliminary Information
U4276B
Ozone Depleting Substances Policy Statement
It is the policy of TEMIC TELEFUNKEN microelectronic GmbH to 1. Meet all present and future national and international statutory requirements. 2. Regularly and continuously improve the performance of our products, processes, distribution and operating systems with respect to their impact on the health and safety of our employees and the public, as well as their impact on the environment. It is particular concern to control or eliminate releases of those substances into the atmosphere which are known as ozone depleting substances ( ODSs). The Montreal Protocol ( 1987) and its London Amendments ( 1990) intend to severely restrict the use of ODSs and forbid their use within the next ten years. Various national and international initiatives are pressing for an earlier ban on these substances. TEMIC TELEFUNKEN microelectronic GmbH semiconductor division has been able to use its policy of continuous improvements to eliminate the use of ODSs listed in the following documents. 1. Annex A, B and list of transitional substances of the Montreal Protocol and the London Amendments respectively 2 . Class I and II ozone depleting substances in the Clean Air Act Amendments of 1990 by the Environmental Protection Agency ( EPA) in the USA 3. Council Decision 88/540/EEC and 91/690/EEC Annex A, B and C ( transitional substances ) respectively. TEMIC can certify that our semiconductors are not manufactured with ozone depleting substances and do not contain such substances.
We reserve the right to make changes to improve technical design and may do so without further notice. Parameters can vary in different applications. All operating parameters must be validated for each customer application by the customer. Should the buyer use TEMIC products for any unintended or unauthorized application, the buyer shall indemnify TEMIC against all claims, costs, damages, and expenses, arising out of, directly or indirectly, any claim of personal damage, injury or death associated with such unintended or unauthorized use. TEMIC TELEFUNKEN microelectronic GmbH, P.O.B. 3535, D-74025 Heilbronn, Germany Telephone: 49 ( 0 ) 7131 67 2831, Fax number: 49 ( 0 ) 7131 67 2423
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Preliminary Information
TELEFUNKEN Semiconductors Rev. A1, 05-Sep-96

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