THS6007 Datasheet, PDF (32/36 Pages) Texas Instruments – DUAL DIFFERENTIAL LINE DRIVERS AND LOW-POWER RECEIVERS

THS6007
DUAL DIFFERENTIAL LINE DRIVERS AND LOW-POWER RECEIVERS
SLOS334– DECEMBER 2000
APPLICATION INFORMATION
general configurations
A common error for the first-time CFB user is to create a unity gain buffer amplifier by shorting the output directly
to the inverting input. A CFB amplifier in this configuration is now commonly referred to as an oscillator. The
THS6007 drivers, like all CFB amplifiers, must have a feedback resistor for stable operation. Additionally,
placing capacitors directly from the output to the inverting input is not recommended. This is because, at high
frequencies, a capacitor has a very low impedance. This results in an unstable amplifier and should not be
considered when using a current-feedback amplifier. Because of this, integrators and simple low-pass filters,
which are easily implemented on a VFB amplifier, have to be designed slightly differently. If filtering is required,
ǒ Ǔǒ Ǔ ^{simply place an RC-filter at the noninverting terminal of the operational-amplifier (see Figure 88).}
RG
RF
+ ) ₎ ^VO
VI
1
RF
RG
1
1
sR1C1
VI
R1
–
+
C1
VO
+ f–3dB
1
2pR1C1
Figure 88. Single-Pole Low-Pass Filter
If a multiple pole filter is required, 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 89.
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 89. 2-Pole Low-Pass Sallen-Key Filter
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