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參數(shù)資料
| 型號： | TDA9614H |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 消費(fèi)家電 |
| 英文描述： | Audio processor for VHS hi-fi and linear audio(應(yīng)用于VHS高保真和線性音頻的音頻處理器) |
| 中文描述： | SPECIALTY CONSUMER CIRCUIT, PQFP64 |
| 封裝： | PLASTIC, QFP-64 |
| 文件頁數(shù)： | 12/60頁 |
| 文件大?。?/td> | 570K |
| 代理商： | TDA9614H |
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1995 Mar 21
12
Philips Semiconductors
Preliminary specification
Audio processor for VHS hi-fi
and linear audio
TDA9614H
(standard play: LP = 0) and 3180 and 170
μ
s (Long Play:
LP = 1).
The signal is DC decoupled and routed to the output select
via pins 29 and 28. When switching to or from playback
the signal should be muted shortly using the Normal
Output Mute (NOM) to prevent audible clicks caused by
offset differences of the playback amplifier and AGC.
6.3
Audio FM circuits
6.3.1
R
ECORD
/
LOOP
-
THROUGH
After low-pass filtering and signal compression in the
Noise Reduction (NR) the audio signal is available at
AFNL and AFNR. Through a DC-decoupling capacitor the
compressed audio signal is fed to an audio clipper at
AFML and AFMR. Subsequently, the audio signal is
FM-modulated on a RF-carrier using an integrated
current-controlled oscillator (CCO). Each CCO (L and R)
requires an external resistor (RCCOL/R) for temperature
stability. Through automatic calibration both the oscillator
centre frequency and FM-deviation are adjusted. After
low-pass filtering and summation of the two RF-carriers,
the FM signal is available at FMOUT during record. During
loop-through the FMOUT pin is inactive.
The RAF pin reflects the status of the RAF-bit when it is
used as output pin. In this case it is meant to switch the
head amplifier between record and playback position. It
can also be used as an input pin to overrule the RAF-bit
thereby forcing the IC in record or playback/loop-through
position.
6.3.2
P
LAYBACK
The two FM modulated RF carriers, presented at FMIN,
are fed to an AGC circuit. The AGC operates on the peak
level of the added BPF output signals. As a result, the input
signal of the BPFs is kept constant for FMIN voltages
>30 mV (RMS value) both carriers added. In this way the
dynamic range of the integrated BPFs is optimally used
over a large input signal range. Subsequently, the
RF carriers are bandpass filtered using two integrated
BPFs. These bandpass filters are automatically calibrated
as described in Section 6.3.3. An external resistor (RBPF)
is required for temperature stability.
The filtered input signals are fed to a limiter. The limiter
output signal is demodulated by means of a
PLL demodulator. The LF audio signal is fed through a
sample-and-hold circuit to suppress head-switching noise.
The demodulated audio is available at AFML and AFMR.
Through a decoupling capacitor the audio signal is applied
to an audio low-pass filter at AFNL and AFNR. The
low-pass filtered audio signal is expanded in the noise
reduction.
If the left channel carrier at FMIN falls below the mute level
of 4.2 mV (RMS value) the audio signal is muted in front of
the low-pass filter. This is achieved by comparing the left
channel level detector signal with an internal reference.
The mute timing is fixed by a capacitor at the CMUTE pin.
If the level at CMUTE rises above a certain threshold, the
PBMUTE bit is set. This will mute the audio signal. If bit
AUTN has been set, the output selection will automatically
switch to NORMAL mode. The left channel level detector
output is also available at pin ENVOUT. An AGC
correction voltage is added at this pin, such that the
ENVOUT voltage indicates the left channel FM-carrier
level even within the AGC-range. The ENVOUT voltage
can be used for auto-tracking of the FM-audio heads.
In the event of drop-outs in the incoming FM signal, the left
channel level detector is also used to activate the
sample-and-hold. This drop-out cancellation is only active
if bit DOC has been set.
6.3.3
A
UTOMATIC CALIBRATION
By means of bit CALS the two integrated oscillators and
bandpass filters can be calibrated in Loop-Through (LT) or
record (REC) mode. Normally this will be done after
start-up of the VCR. After setting of bit CALS the
calibration procedure is automatically executed as shown
in Fig.4. The calibration starts at the first negative edge of
HID after CALS has been set. During the LOW period of
HID (20 ms for PAL) the number of oscillator cycles is
compared to a certain value stored in a Read Only Memory
(ROM).
Therefore, the final oscillator frequency is proportional to
the inverse of the HID LOW-time. This means that an error
of 1
μ
s in the HID LOW-time will result in an additional
frequency error of approximately 100 Hz. The maximum
number of required HID cycles for one complete oscillator
calibration is six, which is equal to 240 ms.
After both oscillators have been calibrated the bandpass
filters are calibrated using the right channel oscillator as
reference frequency generator (1.6 MHz for PAL). This will
take <10 ms.
Bit CALR is set to 1 if the calibration has been executed
successfully. CALR is 0 if:
A Power-On Reset (POR) has occurred.
The calibration is running.
The initial oscillator and bandpass frequencies are too
low or too high for a successful calibration.
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| TDA9615 | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:Audio processor for VHS hi-fi |
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