Datasheet

1
2 R Cp
F F
=
GBP
4 R Cp
F D
f =
-3dB
GBP
2 R Cp
F D
1/2
OPA2890
1/2
OPA2890
High-Speed
DAC
V =I R
O O F
- -V = I R
O O F
R
F1
R
F2
C
F1
C
F2
GBP GainBandwidth®
Product(Hz)fortheOPA2890
C
D1
C
D2
I
O
-I
O
50W
50W
305W
2kW
82.5W
75 CableW
75 LoadW
RG-59
82.5W
75W
750W634W
Video1
+5V
+5V
-5V
1/2
OPA2890
1/2
OPA2890
305W
2kW
75W
750W634W
Video2
-5V
+5V
V
DIS
DISA
DISB
OPA2890
SBOS364C –DECEMBER 2007–REVISED DECEMBER 2009 www.ti.com
HIGH-PERFORMANCE DAC WIDEBAND VIDEO MULTIPLEXING
TRANSIMPEDANCE AMPLIFIER
One common application for video speed amplifiers
High-frequency DDS digital-to-analog converters that include a disable pin is to wire multiple amplifier
(DACs) require a low distortion output amplifier to outputs together, then select one of several possible
retain SFDR performance into real-world loads. video inputs to source onto a single line. This simple
Figure 53 shows a single-ended output drive wired-OR video multiplexer can be easily
implementation. The diagram shows the signal output implemented using the OP2890IDGS (MSOP-10
current(s) connected into the virtual ground summing package only), as shown in Figure 54.
junction(s) of the OPA2890, 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 OPA2890. The dc gain for
this circuit is equal to R
F
. At high frequencies, the
DAC output capacitance (C
D
in Figure 53) produces a
zero in the noise gain for the OPA2890 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, the pole in each
feedback network should be set to:
(1)
which gives a cutoff frequency f
–3dB
of approximately:
(2)
Figure 53. DAC Transimpedance Amplifier
Figure 54. 2-Channel Video Multiplexer (MSOP-10 package only)
18 Submit Documentation Feedback Copyright © 2007–2009, Texas Instruments Incorporated
Product Folder Link(s): OPA2890