Datasheet

50W
OPA4872
R
R
R
R
2R
2R
2R
To50 LoadW
523W
523W
IN0
IN1
IN2
IN3
V
IN
A0
A1
SD
EN
V
OUT
Logic
R =69W
O
OPA4872
To75 LoadW
Logic
R = 69W
O
OPA4872
Logic
523W
523W
523W
523W
EN
SD
EN
SD
R =Z ||( +R +R )
O F GO O
R
1+ =2
R
F
R
G
75W
+5V
-5V
OPA4872
To75 LoadW
Logic
R
2
R
1
R
3
R
4
RedOut
A0 A1
523W
523W
EN
SD
R +R =1046
R =R
W
F G
F G
OPA4872
SBOS346C –JUNE 2007–REVISED MARCH 2011 www.ti.com
2-BIT, HIGH-SPEED ATTENUATOR 8-TO-1 VIDEO MULTIPLEXER
In contrast to the PGA, a two-bit high-speed Two OPA4872s can be used together to form an
attenuator can be implemented by using an R-2R 8-input video multiplexer. The multiplexer is shown in
ladder together with the OPA4872. Figure 29 shows Figure 31.
such an implementation.
Channel 0 sees the full input signal amplitude, where
as channel 1 sees 1/2 V
IN
, channel 2 see 1/4 V
IN
and
channel 3 sees 1/8 V
IN
.
Figure 29. 2-Bit, High-Speed Attenuator,
500MHz Channel Bandwidth
4-INPUT RGB ROUTER
Three OPA4872s can be used together to form a
four-input RGB router. The router for the red
component is shown in Figure 30. Identical stages
would be used for the green and blue channels.
Figure 31. 8-to-1 Video Multiplexer
When connecting OPA4872 outputs together,
maintain a gain of +1V/V at the load. The OPA4872
configuration shown is a gain of +6dB; thus, the
matching resistance must be selected to
achieve –6dB.
The set of equations to solve are shown in
Equation 1 and Equation 2. Here, the impedance of
interest is 75Ω.
(1)
Figure 30. 4-Input RGB Router
(2)
(Red Channel Shown)
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