Datasheet

1/2
OPA2690
1/2
OPA2690
High-Speed
DAC
V =I R
O O F
- -V = I
O O F
R
R
F1
R
F2
C
F1
C
F2
C
D1
C
D2
I
O
-I
O
50W
50W
1
2 R Cp
F F
=
GBP
4 R Cp
F D
f =
-3dB
GBP
2 R Cp
DF
146W
2kW
82.5W
75 CableW
75 LoadW
RG-59
82.5W
75W
402W340W
+5V
+5V
-5V
1/2
OPA2690
1/2
OPA2690
146W
2kW
75W
402W340W
-5V
+5V
V
DIS
DISA
DISB
Video1
Video2
OPA2690
SBOS238G –JUNE 2002–REVISED MARCH 2010 www.ti.com
HIGH-PERFORMANCE DAC
TRANSIMPEDANCE AMPLIFIER
High-frequency, direct digital synthesis (DDS)
digital-to-analog converters (DACs) require a low
distortion output amplifier to retain their SFDR
performance into real-world loads. Figure 40 shows a
single-ended output drive implementation. The
diagram shows the signal output current(s) connected
into the virtual ground summing junction(s) of the
OPA2690, which is set up as a transimpedance stage
or I-V converter. If the DAC requires that its outputs
terminate to a compliance voltage other than ground
for operation, the appropriate voltage level may be
applied to the noninverting input of the OPA2690.
The dc gain for this circuit is equal to R
F
. At high
frequencies, the DAC output capacitance (C
D
in
Figure 40) will produce a zero in the noise gain for
the OPA2690 that may cause peaking in the
closed-loop frequency response. C
F
is added across
R
F
to compensate for this noise gain peaking. To
achieve a flat transimpedance frequency response,
Figure 40. DAC Transimpedance Amplifier
the pole in each feedback network should be set to:
WIDEBAND VIDEO MULTIPLEXING
(1)
One common application for video speed amplifiers
which will give a cutoff frequency, f
−3dB
, of
that include a disable pin is to wire multiple amplifier
approximately:
outputs together, then select which one of several
possible video inputs to source onto a single line.
This simple wired-OR video multiplexer can be easily
implemented using the OP2690I-14D (SO-14
(2)
package only), as shown in Figure 6.
Where GBP = gain bandwidth product (Hz) for the
OPA2690.
Figure 41. Two-Channel Video Multiplexer (SO-14 package only)
16 Copyright © 2002–2010, Texas Instruments Incorporated
Product Folder Link(s): OPA2690