MV95308 Datasheet, PDF (5/9 Pages) Zarlink Semiconductor Inc – 30MHz 8-BIT CMOS VIDEO DAC

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.
MV95308
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_OUT or
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.
Fig.3 Timing diagram
Description
REFWHITE + 10%
REFWHITE
FULL WHITE
OVERBRIGHT
FULL BLACK
BLANK
DATA-SYNC
SYNC
STRDAC MODE
STRDAC
1
1
1
1
1
1
1
1
0
SYNC
1
1
1
1
BLANK
1
1
1
1
REFWHITE OVERBRT
0
0
0
1
1
1
1
0
OUTPUT
DATA
X
X
$FF
DATA
1
1
1
1
1
0
X
X
0
1
1
1
0
0
X
X
X
1
1
X
Table 1: Video output truth table
$00
X
DATA
X
DATA
I_OUT
(LSB)
414
387
387
DATA +
132 + 27
132
111
DATA + 21
0
DATA
3