TDA7540B STMicroelectronics, TDA7540B Datasheet - Page 35

• Manufacturer Part Number: TDA7540B
• Manufacturer: STMicroelectronics

Specifications of TDA7540B

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

DOCUMENT CD00108485
Copyright STMicroelectronics
TDA7540B
4.3.4
4.3.5
REVISION 1.0
block diagram, fig. 16). The MP_OUT-pin is used as detector-output connected to a
capacitor of about 47nF. Using this configuration an external adaptation to the user's
requirement is possible without affecting the "normal" fieldstrength input (LEVEL) for the
stereo decoder.
To keep the old value of the Multipath Detector during an AF-jump, the MP-Hold switch can
disconnect the external capacitor. This switch is controlled directly by the AFS-Pin.
Selecting MPION the channel separation is automatically reduced during a multipath
condition according to the voltage appearing at the MP_OUT-pin.
Programming
To obtain a good multipath performance an adaptation is necessary. Therefore the gain of
the first 19kHz-bandpass is programmable in two steps (MPG), the gain of the second
19kHz-bandpass is programmable in four steps (MPBPG) and the rectifier gain is
programmable in four steps(MPRG). Please note that the frequency of the first multipath
bandpass (MPF) must be set to 19kHz! The attack- and decay-times can be set by the
external capacitor value and the multipath detector charge current MPCC.
Quality detector
The TDA7540 offers a quality detector output, which gives a voltage representing the FM-
reception conditions. To calculate this voltage the MPX-noise and the multipath-detector
output are summed according to the following formula:
The noise-signal is the PEAK-signal without additional influences (see noise blanker
description). The factor 'a' can be programmed from 0.6 to 1.05(QDC) and the factor b can
be programmed from 6dB to 15dB ( QNG). The output is a low impedance output able to
drive external circuitry as well as simply fed to an AD-converter for RDS applications.
AFS control and stereo decoder mute
The TDA7540 is supplied with several functionality to support AF-checks using the stereo
decoder. The additional pin (AFS) is implemented in order to speed up the stereo decoder
AF-functions compared to IIC controlling.
The block diagramm of AFS function is shown in
In order to separate the different functions of the AFS pin, two different logic thresholds are
implemented. Below the higher threshold voltage (2.4V) only the multipath-detector is
switched into small time constant (internal logical signal MPfast).
Below the lower threshold voltage (0.8V) the full AFS function is activated. The MPXIN pin is
switched into high impedance mode (internal signal AFSMute), which avoids any clicks
during the jump condition. If the stereo decoder is not muted, it is possible at the same time
to evaluate the noise- and multipath-content of the alternate frequency using the Quality
detector output.
Furthermore the AFS pin does also freeze the condition of pilot locking and magnitude
(internal signal PDhold). The Pdhold signal is defined by V
PDH signal.
V
Qual
= 0.8b (V
COMPANY INTERNAL
ACTIVE
Noise
-0.8 V)+ a (V
Figure
REF1
17.
th1
-V
or V
Unauthorized reproduction and communication strictly prohibited
Mpout
th2
Functional description
).
, dependent on the
DATE 11-May-2006
31/75
page: 31/75