U4276B TEMIC Semiconductors, U4276B Datasheet - Page 3

• Manufacturer Part Number: U4276B
• Description: FM Multipath Noise Cancellation
• Manufacturer: TEMIC Semiconductors

TELEFUNKEN Semiconductors
Rev. A1, 05-Sep-96
Functional Description
Interference with FM reception can be triggered by vari-
ous causes, such as multipath reception, adjacent and
insufficient field strength. At the same time, multipath re-
ception is responsible for the most frequently occurring
types of interference.
Acoustically relevant multipath interference, since it re-
quires a short reaction time, is suppressed directly by the
circuit via a Multipath Noise Cancellation (MNC) func-
tion.
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:
Multipath Noise Cancellation (MNC)
Extremely strong multipath interference remains audible
in spite of the monoblend function. The remaining inter-
ference 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, ac-
tivation of the MNC depends on the following condition:
System controller
FM – tuner
Fieldstrength
MPX in
Preliminary Information
signal
Figure 1. Block diagram
U4276B
Mute
1. A linear characteristic, i.e. the output voltage must
2. The “signal level” output has to react to extremely
Restrictions
The field strength voltage becomes increasingly noisy in
the range of low RF levels (< 30 dB
vents reliable detection of interference. Therefore, only
the average field strength value can be evaluated over a
relatively large time constant in this range.
– The average field strength must exceed a certain value
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.
so that the noise in the field strength signal does not
cause the MNC to respond at low RF voltages
be proportional to the logarithm of the IF voltage in
the range of RF levels encountered in practice. Devi-
ations from linearity lead to a different evaluation of
interference signals of the same intensity of the signal
levels are different.
fast dips in the field strength. Total field strength fail-
ures lasting 500 ns and occuring a voltage dip to
approx. 0 V at the field strength output.
MPX out
Digital or analogue
processing
signal
95 10633
U4276B
m
V). The noise pre-
AF
AF
right
left
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