1

10

100

6

7

8

9

10

11

12

13

14

FREQUENCY (MHz)

GAIN

PHASE

-180

-135

-90

-45

0

45

90

135

180

LMH6723, LMH6724

SNOSA83I – AUGUST 2003 – REVISED AUGUST 2014

www.ti.com

Inverting Input Parasitic Capacitance (continued)

are inside the feedback loop they have no effect on the gain of the circuit. The circuit shown in Figure 37 has a

gain of 5. The frequency response of this circuit is shown in Figure 38.

Figure 38. Composite Amplifier Frequency Response

7.8 Layout Considerations

Whenever questions about layout arise, use the evaluation board as a guide. Evaluation boards are shipped with

sample requests.

To reduce parasitic capacitances ground and power planes should be removed near the input and output pins.

Components in the feedback loop should be placed as close to the device as possible. For long signal paths

controlled impedance lines should be used, along with impedance matching at both ends.

Bypass capacitors should be placed as close to the device as possible. Bypass capacitors from each rail to

ground are applied in pairs. The larger electrolytic bypass capacitors can be located anywhere on the board;

however, the smaller ceramic capacitors should be placed as close to the device as possible.

7.9 Video Performance

The LMH6723/LMH6724 has been designed to provide good performance with both PAL and NTSC composite

video signals. The LMH6723/LMH6724 is specified for PAL signals. Typically, NTSC performance is marginally

better due to the lower frequency content of the signal. Performance degrades as the loading is increased;

therefore, best performance will be obtained with back terminated loads. The back termination reduces

reflections from the transmission line and effectively masks transmission line and other parasitic capacitances

from the amplifier output stage. Figure 34 shows a typical configuration for driving a 75

Ω cable. The amplifier is

7.10 Single 5-V Supply Video

With a 5V supply the LMH6723/LMH6724 is able to handle a composite NTSC video signal, provided that the

7.10.1 Application Curves

See Figure 31 through Figure 33 and Figure 38.

18

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