LMH6733 Datasheet, PDF (15/25 Pages) Texas Instruments – Single Supply, 1.0 GHz, Triple Operational Amplifier

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LMH6733
SNOSAW0D – JANUARY 2007 – REVISED MAY 2013
HD
Component
Video Input
(Y, Pr, Pb)
LMH6733
VIDEO
VIDEO
RECEIVER EQUALIZER
CAT5 CABLE
LMH6733
LMH6733
VIDEO
RT
TRANSMITTER
RL
Figure 39. CAT5 High Definition Video Transmission
R₁
5 k:
+5V
C₂
0.1 PF
C₃
100 PF
V_IN
R_T
75:
(OPTIONAL)
C₁
10 PF
-+
C_IN
47 PF
R₂
5 k:
R₃
10 k:
+
LMH6733
- ^U1
R₄
680:
+5V
R_G
680:
R_F
340:
C₀
R₀
1000 PF 75:
C₃
1 PF
V_LOAD
R_L
75:
Figure 40. AC Coupled Single Supply Video Amplifier
AC-Coupled Video
The LMH6733 can be used as an AC-coupled single supply video amplifier for driving 75Ω coax with a gain of 2.
The input signal is nominally 0.7V or 1.0V for component YP_RP_B and RGB, depending on the presence of a sync.
R₁, R₂, and R₃ simply set the input to the center of the input linear range while C_IN AC couples the video onto the
op amp’s input.
As can be seen in , Figure 40 amplifier U1 is used in a positive gain configuration set for a closed loop gain of 2.
The feedback resistor R_F is 340Ω. The gain resistor is created from the parallel combination of R_G and R₄, giving
a Thevenin equivalent of 340Ω connected to 2.5V.
The 75Ω back termination resistor R_O divides the signal such that V_OUT equals a buffered version of V_IN. The
back termination will eliminate any reflection of the signal that comes from the load. The input termination
resistor, R_T, is optional – it is used only if matching of the incoming line is necessary. In some applications, it is
recommended that a small valued ceramic capacitor be used in parallel with C_O which is itself electrolytic
because of its rather large value. The ceramic cap will tend to shunt the inductive behavior of this electrolytic
cap, C_O, at higher frequencies for an improved overall, low-impedance output.
Inverting Input Parasitic Capacitance
Parasitic capacitance is any capacitance in a circuit that was not intentionally added. It comes about from
electrical interaction between conductors. Parasitic capacitance can be reduced but never entirely eliminated.
Most parasitic capacitances that cause problems are related to board layout or lack of termination on
transmission lines. Please see the section on Layout Considerations for hints on reducing problems due to
parasitic capacitances on board traces. Transmission lines should be terminated in their characteristic
impedance at both ends.
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