TEA6101 NXP Semiconductors, TEA6101 Datasheet - Page 5

• Manufacturer Part Number: TEA6101
• Manufacturer: NXP Semiconductors

Specifications of TEA6101

• Screening Level: Commercial
• Lead Free Status / Rohs Status: Compliant

Philips Semiconductors
FUNCTIONAL DESCRIPTION
Various forms of disturbance can affect signal reception in
car radio receivers:
The criteria for an antenna diversity system are high
frequency components (spikes and noise) on the audio
signal in combination with variations in signal level.
Detection of spikes on the audio signal
A rectifier, high pass filter, low pass filter and a comparator
are used to detect spikes and noise on the audio signal
(see Fig.1). The negative spikes are detected by the
rectifier whilst a high pass filter removes the audio signal
to leave the high frequency signal components at the
negative input to the comparator. The signal at the positive
input to the comparator consists of an offset together with
an audio signal attenuated by the low pass filter. If the
amplitude of the spikes exceed that of the attenuated
audio plus offset, the output of the comparator is HIGH.
When the switching rate of the comparator is HIGH,
feedback increases the offset via the diode, the resistor
R1, and the 100 nF capacitor. The offset is decreased by
the 12 k resistor and the 100 nF capacitor (pin 11 or 13).
The result is an offset based upon the comparator
switching rate, rapid to increase but slow to decrease,
therefore permitting only the largest spikes to trigger the
comparator (floating threshold).
Should high noise be apparent on the audio signal, the
offset is decreased by means of the rectifier and high pass
filter.
May 1992
ignition interference produces spikes on the audio
signal. Switching to another antenna will be ineffective.
Strong ignition interference, however, will modulate the
antenna field strength. In this instance another antenna
possessing a directional pattern will suffer less
disturbance and switching would be appropriate.
variation of antenna field strength due to travelling
through a zone of variable signal strength will result in a
variation in the signal level. Greater noise will be
apparent on the audio signal whilst the IF limiter is not
limiting. Switching to an alternative antenna input would
increase the signal strength.
multipath reception occurs when a signal reaches the
antenna from two or more directions. Often the signals
will be of different phase. In certain circumstances the
sum of the reflected signals results in zero and a large
spike will be evident on the audio signal. It will then be
necessary to switch to an alternative antenna from
which the sum of the received signals will be different.
Antenna diversity circuit
5
This will result in more frequent switching to an alternative
antenna whilst the result of the switching operation will be
less audible.
Detection of voltage level variation
A 1 F input capacitor and 20 k resistor remove the
absolute level voltage to leave only variations to be
detected. The level comparator output is HIGH when the
variations in level voltage are greater than the offset.
Similarly to the audio comparator; the feedback diode,
resistor R2, the 1 F capacitor and the 33 k resistor
cause the threshold level to float. During periods of high
activity the comparator thus switches only on the largest
variations.
Switching to an alternative antenna
When both the level and the audio comparator outputs are
HIGH, another output of the Johnson counter will be
selected. Since switching to an alternative antenna would
cause a disturbance of the audio and level signals the
monostable multivibrator will prohibit the counter from
selecting another antenna input for 21 s.
Memory and timing
Approximately similar qualities of signal originating from
different antennae could result in unnecessary antenna
switching. This is prevented by appointing a priority
antenna. The selection of an antenna without priority
results in the audio offset being decreased by 1.2 V such
that the audio comparator will have a HIGH output voltage.
During the period of memory timing the offset increases
towards the normal offset value. Should level alterations
occur during this period another antenna will be selected.
If, however, the memory is timed-out without the
occurrence of signal variation, priority will be appointed to
the selected antenna. Thus a priority antenna will be
selected for the majority of the time during reception of
almost all similarly weak antenna signals.
Mute
A mute function should not precede the circuit. This
function is therefore assumed by the TEA6101. When
used in combination with the TEA6100 the 20 k input of
the IF IC together with the 6 k output resistor of the
TEA6101 cause an attenuation of 3 dB. The mute circuit
therefore has 3 dB amplification of level voltages in excess
of 2.75 V.
Objective specification
TEA6101/T