THS4011 Datasheet, PDF (19/30 Pages) Texas Instruments – 290-MHz LOW-DISTORTION HIGH-SPEED AMPLIFIERS

THS4011, THS4012
290-MHz LOW-DISTORTION HIGH-SPEED AMPLIFIERS
APPLICATION INFORMATION
SLOS216B – JUNE 1999 – FEBRUARY 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 amplifer
(see Figure 31).
RG
RF
–
VI
+
VO
R1
C1
ǒ Ǔǒ Ǔ ^{+ f–3dB}
1
2pR1C1
+ ) ₎ ^VO
VI
1
RF
RG
1
1
sR1C1
Figure 31. 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 32. 2-Pole Low-Pass Sallen-Key Filter
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