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MV95308
3
CIRCUIT DESCRIPTION
As illustrated in the function block diagram, Fig. 2, the
MV95308 contains an 8-bit D-to-A converter, input registers,
a loop amplifier and a voltage reference.
On the falling edge of each clock cycle, as shown in Fig. 3,
eight data bits are latched into the device and passed to the
8-bit D-to-A converter. Also latched on the falling edge of the
clock signal, the SYNC and BLANK inputs add the
necessary weighted currents to the analog outputs to
produce the required output levels for use in video
applications. Table 1 details how the SYNC, BLANK,
REFWHITE and OVERBRT inputs modify the DAC output
levels.
To obtain a high data throughput rate, the decoding logic of
the MV95308 is fully pipelined. This introduces a one clock
cycle delay between the latching of the input data and the
resultant DAC output.
It also ensures synchronisation of the internal data and a
minimal output glitch energy.
The DAC employed by the MV95308 eliminates the need
for precision component ratios by using segmented architecture
in which equal weight bit currents are either routed to I
I
OUT
. The use of identical current sources and current steering
their outputs means that monotonicity is guaranteed.
The MV95308 eliminates the need for an external voltage
reference by providing a nominally 1.0V reference on chip. An
on-chip loop amplifier also provides stability of the full scale
output current against power supply and temperature
variations. The full scale output current is set by an external
resistor R
SET
. By adjustment of this value it is possible to
implement RS-343A or RS-170 video levels as explained in the
application notes.
OUT
or
Table 1: Video output truth table
Fig.3 Timing diagram
Description
STRDAC
SYNC
BLANK
REFWHITE
OVERBRT
OUTPUT
DATA
I
OUT
(LSB)
REFWHITE + 10%
1
1
1
0
0
X
414
REFWHITE
1
1
1
0
1
X
387
FULL WHITE
1
1
1
1
1
$FF
387
OVERBRIGHT
1
1
1
1
0
DATA
DATA +
132 + 27
FULL BLACK
1
1
1
1
1
$00
132
BLANK
1
1
0
X
X
X
111
DATA-SYNC
1
0
1
1
1
DATA
DATA + 21
SYNC
1
0
0
X
X
X
0
STRDAC MODE
0
X
1
1
X
DATA
DATA