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CAP3540B Schematic ( PDF Datasheet ) - Micronas

Teilenummer CAP3540B
Beschreibung (CAP3540B / CAP3541B) Car Audio Processor
Hersteller Micronas
Logo Micronas Logo 




Gesamt 36 Seiten
CAP3540B Datasheet, Funktion
MICRONAS
INTERMETALL
PRELIMINARY DATA SHEET
CAP 3540B,
CAP 3541B
Car Audio Processor
Hardware
www.DataSheet4U.com
Edition May 22, 1997
6251-434-1PD
MICRONAS






CAP3540B Datasheet, Funktion
CAP 3540B, CAP 3541B
PRELIMINARY DATA SHEET
2.1.4. Operating Modes
The CAP 3540B possesses 3 main operating modes:
1. MPX-mode
In this mode, the CAP 3540B receives the multiplex sig-
nal of an FM transmission, containing sum and differ-
ence channel, the pilot tone and the signals needed for
travel information (ARI, RDS). The FM-demodulation
has to take place inside the conventional tuner. The mix-
ing of the difference band is done by an analog mixer in
front of the A/D-converters in order to achieve the neces-
sary quality for FM stereo. The ARI and RDS signals and
the pilot tone are extracted digitally.
2. AF-mode
In this mode the CAP 3540B works transparently; the in-
coming signals are A/D-converted and then transmitted
to the DSP core.
3. XDS-mode (not in CAP 3541B)
In this mode there is an external digital source (XDS, e.g.
a CD player) which sends its digital data to the CAP
3540B for further processing and for the reconverting to
analog signals. The CAP 3540B can be adapted to the
sampling rate (32 to 44,1 kHz) prescribed by the external
digital source; in addition the input systems of the CAP
3540B remain active in order to monitor the traffic and
field strength information.
MPX
FM FM
Tuner
IF
FMLEVEL
www.DataSheet4U.com
AM
Tuner & IF
FMTUNOUT
FMOSCIN
AMOSCIN
AMTUNOUT
CAP 3540B
AML
AM LEVEL
LF
LR
RF
RR
Fig. 2–2: CAP 3540B system overview
6
µController
MICRONAS INTERMETALL

6 Page









CAP3540B pdf, datenblatt
CAP 3540B, CAP 3541B
PRELIMINARY DATA SHEET
2.2.7. FM Noise Canceller (ASU)
The FM Noise Canceller removes peak noise from the
audio signal. No external circuitry is required. All filters,
delays and the control section are implemented digitally.
The function is split into two sections:
– The noise detection searches for energy in the non-
audio range by means of a highpass filter. The output
of this filter is compared with a DSP-controlled thresh-
old. If this threshold is exceeded the interpolation unit
is triggered. The 19 kHz pilot tone is removed before
the audio signal enters the detection highpass. Pro-
grammable delay adjustment makes sure of the cor-
rect timing between peak detection and peak inter-
polation.
– The interpolation circuit substitutes a peak-corrupted
sample by the mean value of the non-corrupted adja-
cent samples. Once a trigger comes from the detec-
tion circuit, a programmable number (0 to 15) of
successive samples is interpolated. All functions work
on a 228 kHz sampling rate. At this rate the peaks are
still small enough (not widened by the final decimation
filters) to be removed effectively.
2.3. Analog Output Systems
2.3.1. D/A-Converters DAC
The D/A-converters used are of the oversampling type.
The samples to be converted at their sampling rate f_s
are first interpolated to 8 x the sampling rate and then
oversampled to a higher rate f_NS where noise shaping
iwswpwe.DrfaotramSheede.t4TUh.ceoomutput of the noise shaper is then con-
verted using a highly linear D/A-converter. Its noise pow-
er density increases with increasing frequency, the re-
sidual noise in the baseband is very low.
Only in CAP 3540B:
Within this application the DAC has to be adapted to the
different modes. The digital sources (e.g. CD-player)
must supply the proper clock rate in order to drive the
DAC with a stable clock rate locked to the sampling rate.
The clock is derived from the clock line SCLK of the PDAI
bus.
2.3.2. Lowpass-Filters ALPF
The analog lowpass-filters behind the DACs eliminate
the high-frequent noise in order to avoid any distortions
in the AM frequency range.
12
2.3.3. Volume Control AVOL
The analog volume control together with the digital vol-
ume control implemented in the digital signal proces-
sor’s software provide a large volume control range. The
analog volume control itself covers a range of 45 dB in
1.5 dB steps and includes an additional mute position.
The analog volume control can be adjusted for all 4 out-
put channels individually.
A sensible splitting of the total gain v_tot between the
digital gain v_dig and the analog gain v_anlg is
v_tot
v_totw0 dB
–45 dB<v_tot<0 dB
v_tot<–45 dB
v_anlg
0 dB
v_tot
–45 dB
v_dig
v_tot
0 dB
v_tot+45 dB
All control bits for the hardware section are first ad-
dressed to the DSP core program. In case of hardware
read-registers the bits are transmitted to the DSP core,
stored in the DSP RAM and are thus available for the
controller via the DSP’s IM-bus interface.
2.4. Programmable Digital Audio Interface PDAI
(not included in CAP 3541B)
The PDAI is the digital audio interface between the
CAP 3540B and external digital sources such as CD/MD
player or additional external processors. It offers a large
variety of modes and should therefore cover most of the
digital audio standards (I2S-compatible formats).
Fig. 2–12 shows a standard application with an external
digital source and a second CAP 3540B. The interface
is split into the input section and the output section:
Input Section:
– SCLKI
– SDIN1
– WSI
– ERR
serial clock input
serial data input 1
word select input
error line input
Output Section:
– SCLKO
– SDOUT
– SDIN2
– WSO
serial clock output
serial data output
serial data input 2
word select output
Fig. 2–13 shows the timing of the signals and the pro-
grammable features. The programming is done by writ-
ing the correct bit patterns into the DSP output buffer.
This must be handled by the DSP software.
MICRONAS INTERMETALL

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