THS6022_16 Datasheet, PDF (33/44 Pages) Texas Instruments – 250-mA DUAL DIFFERENTIAL LINE DRIVER

THS6022
www.ti.com
SLOS225D – SEPTEMBER 1998 – REVISED JULY 2007
If a multiple-pole filter is required, the use of a Sallen-Key filter can work very well with CFB amplifiers. This is
because the filtering elements are not in the negative feedback loop and stability is not compromised. Because
of their high slew-rates and high bandwidths, CFB amplifiers can create very accurate signals and help minimize
distortion. An example is shown in Figure 63
C1
V_I
+
R1
R2
_
C2
R1 = R2 = R
C1 = C2 = C
Q = Peaking Factor
(Butterworth Q = 0.707)
f_-3dB
=
1
2pRC
R_F
R_G
R_G
=
R_F
æ
çè ²
-
1
Q
ö
÷ø
Figure 62. Two-Pole Low-Pass Sallen-Key Filter
S0288-01
There are two simple ways to create an integrator with a CFB amplifier. The first one, shown in Figure 64, adds
a resistor in series with the capacitor. This is acceptable because at high frequencies, the resistor is dominant
and the feedback impedance never drops below the resistor value. The second one, shown in Figure 65, uses
positive feedback to create the integration. Caution is advised because oscillations can occur because of the
positive feedback.
R_G
V_I
R_F
C1
–
V_O
+
THS6022
V_O
V_I
=
æ
ççè
R_F
R_G
ö
÷÷ø
æ
ç
ç
ç
ç
S
+
1ö
÷
R_FC1 _÷
S÷
÷
è
ø
Figure 63. Inverting CFB Integrator
S0289-01
R_G
R_F
For Stable Operation:
–
THS6022
+
R2 _³ R_F
V_O
R1|| R_A R_G
R1
V_I
R_A
R2
C1
æ
ç
1
+
R_F
ö
÷
V_O
@
V_I
ç
ç
ç
R_G
sR1C1
÷
÷
÷
è
ø
Figure 64. Noninverting CFB Integrator
S0290-01
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