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Circuit Descriptions, Abbreviation List, and IC Data Sheets

EN 161

BJ2.4U/BJ2.5U LA

•

AGC at vision IF level to give fixed CVBS output level, and
AGC at RF level (tuner AGC) to limit output level of the
tuner.

•

AGC gating for bad reception conditions.

•

CVBS amplitude correction and mute.

•

Detections for AFC and video presence.

The video signal is demodulated by means of an alignment-
free PLL carrier regenerator with an internal VCO. This VCO is
calibrated by means of a digital control circuit, which uses an
external crystal frequency as reference. The frequency setting
for the various standards (33.4, 33.9, 38.0, 38.9, 45.75 and
58.75 MHz) is realized via the I

C bus.

The AFC output is generated by the digital control circuit of the
IF-PLL demodulator and can be read via the I

C bus.

The AGC-detector operates on "top sync" or "top white" level.
The MPIF IC has an integrated sound trap filter. The trap
frequencies can be switched via the I

C-bus.

Also, a group delay correction filter is integrated. The filter can
be switched between the PAL BG curve and a flat group delay
response characteristic. This has the advantage that in multi-
standard receivers the video SAW filter does not need to be
switchable (cost effective).

Analogue Sound IF Processing

Some specifications:
•

A switch to select QSS or inter-carrier mode.

•

Sound carrier frequency conversion at second IF sound
frequency (SSIF)

•

A switch to select internal or external SSIF.

•

AGC at sound IF level (for QSS (quasi-split-sound) mode)
and AGC at SSIF level (for inter-carrier and QSS modes).

•

Demodulation of AM modulated carrier (L and L'
standards).

The MPIF has a separate sound IF input to enable Quasi Split
Sound (QSS) applications. The sound IF amplifier is similar to
the vision IF amplifier and has a gain control range of about 55
dB.
The AGC detector measures the SIF carrier levels (average
level of AM or FM carriers) and ensures a constant signal
amplitude for the AM demodulator and QSS mixer.
For applications without SIF SAW filter, the IC can also be used
in intercarrier mode. In this mode, the composite video signal
from the VIF amplifier is fed to the QSS mixer and converted to
the intercarrier frequency. AM sound demodulation is realized
in the analog domain with the QSS mixer.

9.6.4

Source Selection

Below the main functions and features of the main blocks in the
MPIF for video and audio are explained.

Figure 9-16 MPIF analog source selection block

Video Selectors

The CVI switch (Composite Video Input, including RGB, YUV,
and YPbPr) is selecting the signal from one of the two CVI
inputs; the output is always a YUV signal.
The primary video selector is selecting a signal from the CVBS
and YC inputs; the video coding of the output signal equals to
the video coding of the input signal.
The primary video selector has an extra input (YC_COMB),
capable of selecting an Y/C signal from the comb filter. This
input cannot be downscaled to a CVBS signal and fed back to
the CVBS_A or CVBS_B output. It is also advisable not to
connect other sources to the YC_COMB input because it is
treated as an internal one that is not available for the outside
world.
Two video output selectors are responsible for the contents of
CVBS_A and CVBS_B video out.

Audio Selectors

The primary audio selector is selecting a signal from five
external stereo inputs and one stereo input that handles two
mono signals (AM internal and AM external). The AM internal
signal is demodulated in the IF part and is internally routed, so
not available as external input. Additionally, the AM internal
signal is available on the left channel whereas the AM external
signal is available on the right channel.
The secondary audio selector is selecting a signal from the
same range as the primary audio selector; the second audio
selector can work in stereo or mono mode. In case the stereo
mode is selected, it is alike the primary audio selector. In mono
mode, the input stereo signal L+R is transformed into a mono
signal (L+R)/2 and put on the left channel of the stereo output.
When the stereo input (handling two mono signals) is selected
and the selector works in mono mode, the AMint and AMext
can be swapped on the primary as well as on the secondary
audio channel. It is also possible to digitize the mono + AM on
the secondary audio channel.
Further it is possible to select the AM signal on the analog
audio outputs independently from the AM signal that is selected
for the secondary (digital) audio channel.
Three audio output selectors are responsible for the content of
the Line, SCART1, and SCART2 outputs. These selectors