LMH6601_14 Datasheet, PDF (21/37 Pages) National Semiconductor (TI) – LMH6601/LMH6601Q 250 MHz, 2.4V CMOS Operational Amplifier with Shutdown

LMH6601, LMH6601-Q1
www.ti.com
SNOSAK9E – JUNE 2006 – REVISED MARCH 2013
SINGLE SUPPLY VIDEO APPLICATION
The LMH6601’s high speed and fast slew rate make it an ideal choice for video amplifier and buffering
applications. There are cost benefits in having a single operating supply. Single supply video systems can take
advantage of the LMH6601’s low supply voltage operation along with its ability to operate with input common
mode voltages at or slightly below the V^− rail. Additional cost savings can be achieved by eliminating or reducing
the value of the input and output AC coupling capacitors commonly employed in single supply video applications.
This APPLICATION INFORMATION shows some circuit techniques used to help in doing just that.
DC COUPLED, SINGLE SUPPLY BASEBAND VIDEO AMPLIFIER/DRIVER
The LMH6601 output can swing very close to either rail to maximize the output dynamic range which is of
particular interest when operating in a low voltage single supply environment. Under light output load conditions,
the output can swing as close as a few milli-volts of either rail. This also allows a video amplifier to preserve the
video black level for excellent video integrity. In the example shown below in Figure 52, the baseband video
output is amplified and buffered by the LMH6601 which then drives the 75Ω back terminated video cable for an
overall gain of +1 delivered to the 75Ω load. The input video would normally have a level between 0V to
approximately 0.75V.
VIDEO IN (0-0.75V) ^{VS = 2.7V}
+
LMH6601
R_T
-
75:
75: CABLE
V_LOAD
R_S
75:
R_L
75:
R_G
620:
R_F
620:
Figure 52. Single Supply Video Driver Capable of Maintaining Accurate Video Black Level
With the LMH6601 input common mode range including the V^− (ground) rail, there will be no need for AC
coupling or level shifting and the input can directly drive the non-inverting input which has the additional
advantage of high amplifier input impedance. With LMH6601’s wide rail-to-rail output swing, as stated earlier, the
video black level of 0V is maintained at the load with minimal circuit complexity and using no AC coupling
capacitors. Without true rail-to-rail output swing of the LMH6601, and more importantly without the LMH6601’s
ability of exceedingly close swing to V^−, the circuit would not operate properly as shown at the expense of more
complexity. This circuit will also work for higher input voltages. The only significant requirement is that there is at
least 1.8V from the maximum input voltage to the positive supply (V⁺).
The Composite Video Output of some low cost consumer video equipment consists of a current source which
develops the video waveform across a load resistor (usually 75Ω), as shown in Figure 53 below. With these
applications, the same circuit configuration just described and shown in Figure 53 will be able to buffer and drive
the Composite Video waveform which includes sync and video combined. However, with this arrangement, the
LMH6601 supply voltage needs to be at least 3.3V or higher in order to allow proper input common mode voltage
headroom because the input can be as high as 1V peak.
Copyright © 2006–2013, Texas Instruments Incorporated
Submit Documentation Feedback
21
Product Folder Links: LMH6601 LMH6601-Q1