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參數(shù)資料
| 型號： | 935224690112 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 消費(fèi)家電 |
| 英文描述： | SPECIALTY CONSUMER CIRCUIT, PDIP56 |
| 封裝： | 0.600 INCH, PLASTIC, SOT-400, SDIP-56 |
| 文件頁數(shù)： | 5/75頁 |
| 文件大?。?/td> | 522K |
| 代理商： | 935224690112 |
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1997 Jul 01
13
Philips Semiconductors
Preliminary specication
I2C-bus controlled economy PAL/NTSC
and NTSC TV-processors
TDA837x family
FUNCTIONAL DESCRIPTION
Vision IF amplier
The IF amplifier contains 3 AC-coupled control stages with
a total gain control range which is higher than 66 dB.
The sensitivity of the circuit is comparable with that of
modern IF-ICs.
The video signal is demodulated by a PLL carrier
regenerator. This circuit contains a frequency detector and
a phase detector. During acquisition the frequency
detector will tune the VCO to the correct frequency.
The initial adjustment of the oscillator is realized via the
I2C-bus.
The switching, between SECAM L and L’, can also be
realized via the I2C-bus. After lock-in the phase detector
controls the VCO so that a stable phase relationship
between the VCO and the input signal is achieved.
The VCO operates at twice the IF frequency.
The reference signal for the demodulator is obtained by
using a frequency divider circuit.
The AFC output is obtained by using the VCO control
voltage of the PLL and can be read via the I2C-bus.
For fast search tuning systems the window of the AFC can
be increased by a factor of 3. The setting is realized with
the AFW bit.
Depending on the device type the AGC detector operates
on top-sync level (single standard versions) or on top-sync
and top-white level (multistandard versions).
The demodulation polarity is switched via the I2C-bus.
The AGC detector time constant capacitor is connected
externally. This is mainly because of the flexibility of the
application. The time constant of the AGC system during
positive modulation is rather long, this is to avoid visible
variations of the signal amplitude. To improve the speed of
the AGC system, a circuit has been included which detects
whether the AGC detector is activated every frame period.
When, during 3 frame periods, no action is detected the
speed of the system is increased. For signals without
peak-white information the system switches automatically
to a gated black level AGC. Because a black level clamp
pulse is required for this method of operation the circuit will
only switch to black level AGC in the internal mode.
The circuits contain a second fast video identification
circuit which is independent of the synchronization
identification circuit. Consequently, search tuning is also
possible when the display section of the receiver is used
as a monitor. However, this identification circuit cannot be
made as sensitive as the slower sync identification circuit
(SL) and it is recommended to use both identification
outputs to obtain a reliable search system.
The identification output is applied to the tuning system via
the I2C-bus.
The input of the identification circuit is connected to pin 13,
the internal CVBS input (see Fig.1). This has the
advantage that the identification circuit can also be made
operative when a scrambled signal is received
[descrambler connected between the IF video output
(pin 6) and pin 13]. A second advantage is that the
identification circuit can be used when the IF amplifier is
not used (e.g. with built-in satellite tuners).
The video identification circuit can also be used to identify
the selected CBVS or Y/C signal. The switching between
the two modes can be realized with bit VIM.
Video switches
The circuit has two CVBS inputs (CVBSint and CVBSext)
and a Y/C input. When the Y/C input is not required pin 11
can be used as the third CVBS input. The switch
configuration is illustrated in Fig.7. The selection of the
various sources is made via the I2C-bus.
The output signal of the CVBS switch is externally
available and can be used to drive the teletext decoder, the
SECAM add-on decoder and a comb filter.
In applications with comb filters a Y/C input is only possible
when additional switches are added. In applications
without comb filters the Y/C input signal can be switched
to the CVBS output.
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