Datasheet

OPA695
20
SBOS293G
www.ti.com
FIGURE 11. High-Resolution RGB Driver Using DAC Complementary Output Current.
bandwidth of 600MHz, which will then support up to 1.26GHz
pixel rates. Figure 10 shows an example where three
OPA695s provide an auxiliary monitor output for a high-
resolution RGB RAMDAC.
An alternative circuit that will take advantage of the higher
inverting slew rate of the OPA695 (4300V/µs) takes the
complementary current output from the RAMDAC and con-
verts it to positive video to give a very high, full-power
bandwidth RGB line driver. This will give sharper pixel edges
than the circuit of Figure 10. Most high-speed DACs are
current-steering designs where there is both an output
current signal that is used for the video, and a complemen-
OPA695
75Ω
R
F
500Ω
R
G
536Ω
R
T
86.6Ω
+5V
Power supply decoupling not shown.
–5V
RAMDAC
768Ω
4.22kΩ
0.77V
20Ω
0.1µF
DIS
I
O
tary output that is typically discarded into a matching resistor.
The complementary current output can be used as an aux-
iliary output if it is inverted, as shown in Figure 11.
In the circuit of Figure 11, the complementary current output
is terminated by an equivalent 75Ω impedance (the parallel
combination of R
T
and R
G
) that also provides a current
division to reduce the signal current through the feedback
resistor, R
F
. This allows R
F
to be increased to a value which
will hold a flat frequency response. Since the complementary
current output is essentially an inverted video signal, this
circuit sets up a white video level at the output of the OPA695
for zero DAC output current (using the 0.77V DC bias on the
FIGURE 10. Gain of +2, High-Resolution RGB Monitor Output.
OPA695
75Ω
75Ω
511Ω
R
F
511Ω
20Ω
+5V
Blue
–5V
75Ω
Green
RAMDAC
75Ω
Red
Addtional
OPA695
Stages
DIS
Power supply decoupling not shown.