LMH6722MA National Semiconductor, LMH6722MA Datasheet - Page 11

• Manufacturer Part Number: LMH6722MA
• Description: Operational Amplifier (Op-Amp) IC
• Manufacturer: National Semiconductor

Specifications of LMH6722MA

• No. Of Pins: 14
• Peak Reflow Compatible (260 C): No
• Supply Voltage Max: 12 V
• Leaded Process Compatible: No
• Package / Case: 14-NSOIC
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Section
WIDE BAND DIGITAL PROGRAMMABLE GAIN AMPLIFIER (LMH6720 ONLY)
As shown in Figure 6 and Figure 7 the LMH6720 can be
used to construct a digitally controlled programmable gain
amplifier. Each amplifier is configured to provide a digitally
selectable gain. To provide for accurate gain settings, 1% or
better tolerance is recommended on the feedback and gain
resistors. The gain provided by each digital code is arbitrary
through selection of the feedback and gain resistor values.
AMPLITUDE EQUALIZATION
Sending signals over coaxial cable greater than 50 meters in
length will attenuate high frequency signal components
much more than lower frequency components. An equalizer
can be made to pre emphasize the higher frequency com-
ponents so that the final signal has less distortion. This
process can be done at either end of the cable. The circuit in
Figure 8 shows a receiver with some additional components
FIGURE 6. Wideband Digitally Controlled Programmable Gain Amplifier
(Continued)
FIGURE 7. PGA Output
Channel Switching
11
in the feedback loop to equalize the incoming signal. The RC
networks peak the signal at higher frequencies. This peaking
is a piecewise linear approximation of the inverse of the
frequency response of the coaxial cable. Figure 9 shows the
effect of this equalization on a digital signal that has passed
through 150 meters of coaxial cable. Figure 10 shows a
Bode plot of the frequency response of the circuit in Figure 8
along with equations needed to design the pole and zero
frequencies. Figure 11 shows a network analyzer plot of an
LMH6714/6720/6722 with the following component values:
R
R1 = 450Ω
C1 = 470pF
R2 = 91Ω
C2 = 68pF
G
= 309Ω
20056520
20056519
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