Datasheet

HIGH-PERFORMANCE DAC WIDEBAND VIDEO MULTIPLEXING
1
2 R Cp
F F
=
GBP
4 R Cp
F D
(1)
f =
-3dB
GBP
2 R Cp
F D
(2)
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OPA2889
C
D1
C
D2
I
O
-I
O
50W
50W
1/2
OPA2889
1/2
OPA2889
146W
2kW
82.5W
75 CableW
75 LoadW
RG-59
82.5W
75W
402W340W
Video1
+5V
+5V
-5V
146W
2kW
75W
402W340W
Video2
-5V
+5V
V
DIS
DISA
DISB
1/2
OPA2889
1/2
OPA2889
OPA2889
SBOS373B – JUNE 2007 – REVISED AUGUST 2008 ....................................................................................................................................................... www.ti.com
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 their SFDR performance into real-world loads. video inputs to source onto a single line. This simple
Figure 54 shows a single-ended output drive wired-OR video multiplexer can be easily
implementation. The diagram shows the signal output implemented using the OP2889IDGS (MSOP-10
current(s) connected into the virtual ground summing package only), as shown in Figure 55 .
junction(s) of the OPA2889, 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 OPA2889. The dc gain for
this circuit is equal to R
F
. At high frequencies, the
DAC output capacitance (C
D
in Figure 54 ) produces a
zero in the noise gain for the OPA2889 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:
which gives a cutoff frequency f
– 3dB
of approximately:
Figure 54. DAC Transimpedance Amplifier
Figure 55. 2-Channel Video Multiplexer (SO-14 package only)
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Product Folder Link(s): OPA2889