THS6022 Datasheet, PDF (34/38 Pages) Texas Instruments – 250-mA DUAL DIFFERENTIAL LINE DRIVER

THS6022
250-mA DUAL DIFFERENTIAL LINE DRIVER
SLOS225C – SEPTEMBER 1998 – REVISED JANUARY 2000
APPLICATION INFORMATION
general configurations (continued)
RG
RF
–
ǒ Ǔǒ Ǔ + ) ₎ ^VO
VI
1
RF
RG
1
1
sR1C1
VI
R1
+
C1
VO
+ f–3dB
1
2pR1C1
Figure 61. Single-Pole Low-Pass Filter
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
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 62. 2-Pole Low-Pass Sallen-Key Filter
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.
RG
VI
RF
C1
–
+
VO
THS6022
ǒ Ǔ_{ȧȡ ȧȣ} + ^{) VO}
RF
S
1
RFC1
Ȣ Ȥ ^VI
RG
S
Figure 63. Inverting CFB Integrator
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