THS4031-EP Datasheet, PDF (25/37 Pages) Texas Instruments – 100-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS

THS4031-EP
THS4032-EP
www.ti.com........................................................................................................................................................................................... SLOS610 – NOVEMBER 2008
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 58).
R_G
R_F
V_I
R1
−
+
V_O
C1
f–3dB
+
1
2pR1C1
ǒ Ǔǒ Ǔ ^VO
VI
+
1
)
RF
RG
1
1 ) sR1C1
Figure 58. 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
V_I
R1
+
R2
_
C2
R_F
R_G
R1 = R2 = R
C1 = C2 = C
Q = Peaking Factor
(Butterworth Q = 0.707)
f–3dB
+
1
2pRC
( ) ^{RG =}
R_F
1
2– _Q
Figure 59. Two-Pole Low-Pass Sallen-Key Filter
Copyright © 2008, Texas Instruments Incorporated
Submit Documentation Feedback
25
Product Folder Link(s): THS4031-EP THS4032-EP