THS4051 Datasheet, PDF (19/30 Pages) Texas Instruments – 70-MHz HIGH-SPEED AMPLIFIERS

THS4051, THS4052
70-MHz HIGH-SPEED AMPLIFIERS
APPLICATION INFORMATION
SLOS238C– MAY 1999 – REVISED MAY 2000
general configurations
When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is often
required. The simplest way to accomplish this is to place an RC filter at the noninverting terminal of the amplifier
(see Figure 49).
RG
RF
VI
R1
–
+
VO
C1
+ f–3dB
1
2pR1C1
ǒ Ǔǒ Ǔ + ) ₎ ^VO
VI
1
RF
RG
1
1
sR1C1
Figure 49. Single-Pole Low-Pass Filter
If even more attenuation is needed, a multiple pole filter is required. The Sallen-Key filter can be used for this
task. For best results, the amplifier should have a bandwidth that is 8 to 10 times the filter frequency bandwidth.
Failure to do this can result in phase shift of the amplifier.
C1
VI
R1
+
R2
_
C2
RF
RG
R1 = R2 = R
C1 = C2 = C
Q = Peaking Factor
(Butterworth Q = 0.707)
+ f–3dB
1
2pRC
( ) ^{RG =}
RF
1
2– _Q
Figure 50. 2-Pole Low-Pass Sallen-Key Filter
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