TDA7540B STMicroelectronics, TDA7540B Datasheet - Page 29

• Manufacturer Part Number: TDA7540B
• Manufacturer: STMicroelectronics

Specifications of TDA7540B

• Case: TQFP
• Dc: 06+
• Lead Free Status / Rohs Status: Compliant

DOCUMENT CD00108485
Copyright STMicroelectronics
TDA7540B
4.1.4
REVISION 1.0
is made by charge and discharge current after comparator1 in an external capacitance. The
charge current is fixed and the discharge current is controlled by I
produces digital signals (ac, ac+) in an additional comparator4. The adjacent channel
information is available as analog output signal after rectifier and +8dB output buffer.
Multipath detector
The input of the multipath detector is AC coupled from internal unweighted fieldstrength. A
programmable bandpass (MPF) and amplifier (MPG) as well as rectifier determines the
influences. This voltage is compared with an adjustable comparator2 thresholds (MPTH).
The output signal of this comparator2 is used for the "Milano" effect. In this case the
adjacent channel detection is switched off. The "Milano" effect is selectable by I
(MPOFF). The multipath information is available as analog output signal after rectifier and
+8dB output buffer.
450kHz IF narrow bandpass filter (ISS filter)
The device gets an additional 450KHz IF narrow bandpass filter for suppression of noise
and adjacent channel signal influences. This narrow filter has three switchable bandwidthes,
narrow range of 80kHz, mid range of 120kHz and 30KHz for weather band information.
Without ISS filter the IF bandwidth (wide range) is defined only by ceramic filter chain. The
filter is located between mixer2 and 450kHz limiter stage. The centre frequency is matched
to the demodulator center frequency.
Deviation detector
In order to avoid distortion in audio output signal the narrow ISS filter is switched OFF for
present overdeviation. Hence the demodulator output signal is detected. A lowpass filtering
and peak rectifier generates a signal that is defined by software controlled current (TDEV) in
an external capacitance.
This value is compared with a programmable comparator3 thresholds (DWTH, DTH) and
generates two digital signals (dev, dev+). For weak signal condition deviation threshold is
dependent on FSWO.
ISS switch logic
All digital signals coming from adjacent channel detector, deviation detector and softmute
are acting via switching matrix on ISS filter switch. The IF bandpass switch mode is
controlled by software (ISSON, ISS30, ISS80, CTLOFF). The switch ON of the IF bandpass
is also available by external manipulation of voltage at PIN27. Two application modes are
available (APPM).
The conditions are described in table 51.
Soft mute control
The filtered fieldstrength (FSWO) signal is the reference for mute control. The startpoint and
mute depth are programmable (SMTH, SMD) in a wide range. The time constant is defined
by external capacitance. Additional adjacent channel mute function is supported. A
highpass filter with -3dB threshold frequency of 100kHz, amplifier and peak rectifier
generates an adjacent noise signal from MPX output with the same time constant for
softmute. This value is compared with comparator5 thresholds (ACM). For present strong
adjacent channel the MPX signal is additional attenuated (ACMD).
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2
C Bus. This level
Functional description
DATE 11-May-2006
2
C Bus
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