OPA4872-EP Datasheet, PDF (13/24 Pages) Texas Instruments – 4:1 HIGH-SPEED MULTIPLEXER

OPA4872-EP
www.ti.com........................................................................................................................................................................................... SBOS444 – DECEMBER 2008
2-BIT, HIGH-SPEED ATTENUATOR
In contrast to the PGA, a two-bit high-speed
attenuator can be implemented by using an R-2R
ladder together with the OPA4872. Figure 29 shows
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.
8-TO-1 VIDEO MULTIPLEXER
Two OPA4872s can be used together to form an
8-input video multiplexer. The multiplexer is shown in
Figure 31.
OPA4872
EN
SD
V_IN
2R
2R
2R
R
IN0
R
IN1
R
IN2
R
IN3
OPA4872
SD
EN
50W
V_OUT
523W
To 50W Load
523W
Logic
R_O = 69W
523W
523W
To 75W Load
Logic
A0 A1
Figure 29. 2-Bit, High-Speed Attenuator,
500MHz Channel Bandwidth
OPA4872
EN
SD
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.
+5V
OPA4872
EN
R₁
SD
R₂
75W
Red Out
R₃
523W _{To 75W Load}
523W
R₄
Logic
A0 A1
-5V
Figure 30. 4-Input RGB Router
(Red Channel Shown)
R_O = 69W
523W
523W
Logic
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 +6 dB; thus, the
matching resistance must be selected to achieve
–6 dB.
The set of equations to solve is shown in Equation 1
and Equation 2. Here, the impedance of interest is
75 Ω.
R_O = Z_O || (R_O + R_F + R_G)
1 + ^RF = 2
R_G
(1)
R_F + R_G = 1046W
R_F = R_G
(2)
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): OPA4872-EP
Submit Documentation Feedback
13