LMH6601Q NSC [National Semiconductor], LMH6601Q Datasheet - Page 22

• Manufacturer Part Number: LMH6601Q
• Description: 250 MHz, 2.4V CMOS Operational Amplifier with Shutdown
• Manufacturer: NSC [National Semiconductor]

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If a stage has a 3 V
a given node, as shown in Figure 11, the maximum allowable
amplitude for an arbitrary waveform is ½ of 3V or 1.5 V
is due to the shift in the average value of the waveform as the
duty cycle varies. Figure 11 shows what would happen if a
2 V
as the one in Figure 11B, would have high positive excur-
sions. At low enough duty cycles, the waveform could get
clipped on the top, as shown, or a more subtle loss of linearity
could occur prior to full-blown clipping. The converse of this
occurs with high duty cycle waveforms and negative clipping,
as depicted in Figure 11C.
TV_NTSC
Standard
PP
Video
SVGA
SXGA
UXGA
VGA
XGA
signal were applied. A low duty cycle waveform, such
1280x1024
1600x1200
TABLE 2. Rise Time, −3 dB BW, and Slew Rate Requirements for Various Video Line Rates
Line Rate
1024x768
451x483
640x480
800x600
(HxV)
PP
unclipped swing capability available at
FIGURE 11. Headroom Considerations with AC Coupled Amplifiers
Refresh Rate
(Hz)
30
75
75
75
75
75
Active (KH%)
Horizontal
PP
84
80
76
77
75
74
. This
22
Active (KV%)
HOW TO PICK THE RIGHT VIDEO AMPLIFIER
Apart from output current drive and voltage swing, the op amp
used for a video amplifier/cable driver should also possess
the minimum requirement for speed and slew rate. For video
type loads, it is best to consider Large Signal Bandwidth (or
LSBW in the National Semiconductor data sheet tables) as
video signals could be as large as 2 V
commonly used gain of +2 configuration. Because of this rel-
atively large swing, the op amp Slew Rate (SR) limitation
should also be considered. Table 2 shows these require-
ments for various video line rates calculated using a rudimen-
tary technique and intended as a first order estimate only.
Vertical
92
95
96
95
96
96
Pixel Time
118.3
33.0
20.3
12.4
(ns)
7.3
4.9
Rise Time
39.4
11.0
(ns)
6.8
4.1
2.4
1.6
PP
when applied to the
LSBW
(MHz)
20136452
143
213
32
52
85
9
(V/μs)
146
237
387
655
973
SR
41