THS4120 Datasheet, PDF (17/23 Pages) Texas Instruments – HIGH-SPEED FULLY DIFFERENTIAL I/O AMPLIFIERS

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PRINCIPLES OF OPERATION (continued)
THS4120
THS4121
SLOS319D – FEBRUARY 2001 – REVISED OCTOBER 2004
3.3 V
PD
10 kW
+
THS4120
V_IN
_
V_OCM
Figure 28.
Due to the similarity of the standard inverting amplifier configuration, the output impedance appears to be low
while in the power-down state. This is because the feedback resistor (R_f) and the gain resistor (R_(g)) are still
connected to the circuit. Therefore, a current path is allowed between the input of the amplifier and the output of
the amplifier. An example of the closed-loop output impedance is shown in Figure 29.
10000
THS4120
SINGLE-ENDED OUTPUT IMPEDANCE
(IN POWER DOWN)
vs
FREQUENCY
V_CC = 3.3 V
1000
100
10
100 k
1M
10 M
100 M
1G
f − Frequency − Hz
Figure 29.
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