THS4031 Datasheet, PDF (27/38 Pages) Texas Instruments – 100-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS

THS4031, THS4032
100-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS
APPLICATION INFORMATION
SLOS224C – JULY 1999 – REVISED APRIL 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 52).
RG
RF
–
VI
+
VO
R1
C1
ǒ Ǔǒ Ǔ ^{+ f–3dB}
1
2pR1C1
+ ) ₎ ^VO
VI
1
RF
RG
1
1
sR1C1
Figure 52. 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.
Otherwise, phase shift of the amplifier can occur.
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 53. 2-Pole Low-Pass Sallen-Key Filter
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