ADV7121KN30 AD [Analog Devices], ADV7121KN30 Datasheet - Page 7

• Manufacturer Part Number: ADV7121KN30
• Description: CMOS 80 MHz, Triple 10-Bit Video DACs
• Manufacturer: AD [Analog Devices]

TERMINOLOGY
Blanking Level
The level separating the SYNC portion from the video portion
of the waveform. Usually referred to as the front porch or back
porch. At 0 IRE units, it is the level which will shut off the pic-
ture tube, resulting in the blackest possible picture.
Color Video (RGB)
This usually refers to the technique of combining the three pri-
mary colors of red, green and blue to produce color pictures
within the usual spectrum. In RGB monitors, three DACs are
required, one for each color.
Sync Signal (SYNC)
The position of the composite video signal which synchronizes
the scanning process.
Gray Scale
The discrete levels of video signal between reference black and
reference white levels. A 10-bit DAC contains 1024 different
levels, while an 8-bit DAC contains 256.
Raster Scan
The most basic method of sweeping a CRT one line at a time to
generate and display images.
Reference Black Level
The maximum negative polarity amplitude of the video signal.
Reference White Level
The maximum positive polarity amplitude of the video signal.
Sync Level
The peak level of the SYNC signal.
Video Signal
That portion of the composite video signal which varies in gray
scale levels between reference white and reference black. Also
referred to as the picture signal, this is the portion which may be
visually observed.
CIRCUIT DESCRIPTION & OPERATION
The ADV7121/ADV7122 contains three 10-bit D/A converters,
with three input channels, each containing a 10-bit register.
Also integrated on board the part is a reference amplifier. CRT
control functions BLANK and SYNC are integrated on board
the ADV7122.
REV. B
(R0–R9, G0–G9, B0–B9;
ANALOG OUTPUTS
DIGITAL INPUTS
SYNC, BLANK)
(IOR, IOG, IOB)
CLOCK
Figure 2. Video Data Input/Output
–7–
Digital Inputs
Thirty bits of pixel data (color information) R0–R9, G0–G9 and
B0–B9 are latched into the device on the rising edge of each
clock cycle. This data is presented to the three 10-bit DACs and
is then converted to three analog (RGB) output waveforms. See
Figure 2.
The ADV7122 has two additional control signals, which are
latched to the analog video outputs in a similar fashion. BLANK
and SYNC are each latched on the rising edge of CLOCK to
maintain synchronization with the pixel data stream.
The BLANK and SYNC functions allow for the encoding of
these video synchronization signals onto the RGB video output.
This is done by adding appropriately weighted current sources
to the analog outputs, as determined by the logic levels on the
BLANK and SYNC digital inputs. Figure 3 shows the analog
output, RGB video waveform of the ADV7121/ADV7122. The
influence of SYNC and BLANK on the analog video waveform
is illustrated.
Table I details the resultant effect on the analog outputs of
BLANK and SYNC.
All these digital inputs are specified to accept TTL logic levels.
Clock Input
The CLOCK input of the ADV7121/ADV7122 is typically the
pixel clock rate of the system. It is also known as the dot rate.
The dot rate, and hence the required CLOCK frequency, will be
determined by the on-screen resolution, according to the follow-
ing equation:
Dot Rate = (Horiz Res)
Horiz Res
Vert Res
Refresh Rate
Retrace Factor
DATA
(Retrace Factor)
= Number of Pixels/Line.
= Number of Lines/Frame.
= Horizontal Scan Rate. This is the rate at
= Total Blank Time Factor. This takes into
which the screen must be refreshed, typ-
ically 60 Hz for a noninterlaced system or
30 Hz for an interlaced system.
account that the display is blanked for a
certain fraction of the total duration of
each frame (e.g., 0.8).
(Vert Res)
ADV7121/ADV7122
(Refresh Rate)/