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參數資料
| 型號： | TDA9875AH/V2,557 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 消費家電 |
| 英文描述： | SPECIALTY CONSUMER CIRCUIT, PQFP64 |
| 封裝： | PLASTIC, QFP |
| 文件頁數： | 3/96頁 |
| 文件大小： | 324K |
| 代理商： | TDA9875AH/V2,557 |
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1999 Dec 20
11
Philips Semiconductors
Product specication
Digital TV Sound Processor (DTVSP)
TDA9875A
6
FUNCTIONAL DESCRIPTION
6.1
Demodulator and decoder section
6.1.1
SIF INPUT
Two input pins are provided: SIF1 e.g. for terrestrial TV
and SIF2 e.g. for a satellite tuner. For higher SIF signal
levels the SIF input can be attenuated with an internal
switchable
10 dB resistor divider. As no specific filters are
integrated, both inputs have the same specification giving
flexibility in application. The selected signal is passed
through an AGC circuit and then digitized by an 8-bit ADC
operating at 24.576 MHz.
6.1.2
AGC
The gain of the AGC amplifier is controlled from the ADC
output by means of a digital control loop employing
hysteresis. The AGC has a fast attack behaviour to
prevent ADC overloads and a slow decay behaviour to
prevent AGC oscillations. For AM demodulation the AGC
must be switched off. When switched off, the control loop
is reset and fixed gain settings can be chosen
(see Table 15).
The AGC can be controlled via the I2C-bus. Details can be
found in the I2C-bus register definitions (see Chapter 10).
6.1.3
MIXER
The digitized input signal is fed to the mixers, which mix
one or both input sound carriers down to zero IF. A 24-bit
control word for each carrier sets the required frequency.
Access to the mixer control word registers is via the
I2C-bus. When receiving NICAM programs, a feedback
signal is added to the control word of the second carrier
mixer to establish a carrier-frequency loop.
6.1.4
FM AND AM DEMODULATION
An FM or AM input signal is fed via a band-limiting filter to
a demodulator that can be used for either FM or AM
demodulation. Apart from the standard (fixed)
de-emphasis characteristic, an adaptive de-emphasis is
available for encoded satellite programs. A stereo decoder
recovers the left and right signal channels from the
demodulated sound carriers. Both the European and
Korean stereo systems are supported.
6.1.5
FM IDENTIFICATION
The identification of the FM sound mode is performed by
AM synchronous demodulation of the pilot signal and
narrow-band detection of the identification frequencies.
The result is available via the I2C-bus interface. A selection
can be made via the I2C-bus for B/G, D/K and M standard
and for three different modes that represent different
trade-offs between speed and reliability of identification.
6.1.6
NICAM DEMODULATION
The NICAM signal is transmitted in a DQPSK code at a bit
rate of 728 kbit/s. The NICAM demodulator performs
DQPSK demodulation and feeds the resulting bitstream
and clock signal onto the NICAM decoder and, for
evaluation purposes, to pins PCLK and NICAM.
A timing loop controls the frequency of the crystal oscillator
to lock the sampling rate to the symbol timing of the
NICAM data.
6.1.7
NICAM DECODER
The device performs all decoding functions in accordance
with the
“EBU NICAM 728 specification”. After locking to
the frame alignment word, the data is descrambled by
applying the defined pseudo-random binary sequence and
the device will then synchronize to the periodic frame flag
bit C0.
Bit VDSP (see Section 10.4.1) indicates that the decoder
has locked to the NICAM data and that the data is valid
sound data.
The status of the NICAM decoder can be read out from the
NICAM status register by the user (see Section 10.4.2).
Bit OSB indicates that the decoder has locked to the
NICAM data. Bit C4 indicates that the sound conveyed by
the FM mono channel is identical to the sound signal
conveyed by the NICAM channel.
The error byte contains the number of sound sample
errors, resulting from parity checking, that occurred in the
past 128 ms period. The Bit Error Rate (BER) can be
calculated using the following equation:
BER
bit errors
total bits
-----------------------
error byte
1.74
×
10
5
–
×
≈
=
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相關代理商/技術參數 |
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| TDA9880 | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Alignment-free multistandard vision and FM sound IF-PLL demodulator |
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