STV0056A STMicroelectronics, STV0056A Datasheet - Page 9

• Manufacturer Part Number: STV0056A
• Description: Video ICs Analog Sound/Video
• Manufacturer: STMicroelectronics
• Type: Audio DSPr

Specifications of STV0056A

• Maximum Operating Temperature: + 70 C
• Package / Case: PDIP-56
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

CIRCUIT DESCRIPTION
Video Section
The composite video is first set to a standard level
by means of a 64 step gain controlled amplifier. In
the case that the modulation is negative,an inverter
can be switched in.
One of two different external video de-emphasis
networks (for instance PAL and NTSC) is select-
able by an integrated bus controlled switch.
Then energy dispersal is removed by a sync tip
clamping circuit, which is used on all inputs to a
video switching matrix, thus making sure that no
DC steps occur when switching video sources.
The matrix can be used to feed video to and from
decoders, VCR’s and TV’s.
A bus controlled black level adjustment circuit is
provided on the decoder output allowing a direct
connection to an on-board Videocrypt decoder.
Additionaly all the video outputs are tristate type
(high impedance mode is supported), allowing a
simple parallel connections to the scarts (Twin
tuner applications).
Audio Section
The two audio channels are totally independent
except for the possibility given to output on both
channels only one of the selected input audio chan-
nels.
To allow a very cost effective application, each
channel uses PLL demodulation. Neither external
complex filter nor ceramic filters are needed.
The frequency of the demodulated subcarrier is
chosen by a frequency synthesizer which sets the
frequency of the internal local oscillator by com-
paring its phase with the internally generated
reference. When the frequency is reached, the
microprocessor switches in the PLL and the de-
modulationstarts. At any moment the microproces-
sor can read from the device (watchdog registers)
the actual frequency to which the PLL is locked. It
can alsoverify that a carrier is present at the wanted
frequency (by reading AMPLK status bit) thanks to
a synchronous amplitude detector, which is also
used for the audio input AGC.
In order to maintain constant amplitude of the
recovered audio regardless of variations between
satellites or subcarriers, the PLL loop gain may be
programmed from 56 values.
Any frequency deviation can be accomodated
(from 30kHz till 400kHz).
Two different networks can be permanently con-
nected for either 75 s or J17 de-emphasis. If 50 s
de-emphasisis required, this can be inserted by an
internal switch, thus allowing a worldwide applica-
tion.
The STV0056A is intended to be compatible with
Wegener Panda System.
Two types of audio outputs are provided : one is a
fixed 1V
2V
to -26.75dBwith 1.25dB steps. This output can also
be muted.
A matrix is implemented to feed audio to and from
decoders VCR’s and TV’s.
Noise reduction system and de-emphasis can be
inserted or by-passed through bus control.
Also all the audio outputs are tristate-type (high
impedance mode is supported), allowing a simple
parallel connections to the scarts (Twin tuner appli-
cations).
Others
A 22kHz tone is generated for LNB control.
It is selectable by bus control and available on one
of the two pins connected to the external video
de-emphasis networks. One general purpose I/O
is also available on the STV0056A.
By means of the I
drive the ICs into a low power consumption mode
with active audio and video matrixes. Inde-
pendantly from the main power mode, each indi-
vidual audio and video output can be driven to high
impedance mode.
RMS
max. The control range being from +12dB
RMS
and the other is a gain controlled
2
C bus there is the possibility to
STV0056A
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