THS4021_16 Datasheet, PDF (12/29 Pages) Texas Instruments – 350-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS

THS4021
THS4022
SLOS265C – SEPTEMBER 1999 – REVISED JULY 2007
www.ti.com
Driving a Capacitive Load
Driving capacitive loads with high-performance amplifiers is not a problem as long as certain precautions are
taken. The first is to realize that the THS402x has been internally compensated to maximize its bandwidth and
slew-rate performance. When the amplifier is compensated in this manner, capacitive loading directly on the
output decreases the device phase margin, leading to high-frequency ringing or oscillations. Therefore, for
capacitive loads of greater than 10 pF, it is recommended that a resistor be placed in series with the output of
the amplifier, as shown in Figure 33. A minimum value of 20 Ω should work well for most applications. For
example, in 75-Ω transmission systems, setting the series resistor value to 75 Ω both isolates any capacitance
loading and provides the proper line impedance matching at the source end.
1 kW
Input
50 W
_
THS402x
+
20 W
Output
C_LOAD
Figure 33. Driving a Capacitive Load
S0278-01
Offset Nulling
The THS402x has very low input offset voltage for a high-speed amplifier. However, if additional correction is
required, an offset nulling function has been provided on the THS4021. The input offset can be adjusted by
placing a potentiometer between terminals 1 and 8 of the device and tying the wiper to the negative supply. This
is shown in Figure 34.
V_CC+
+
THS402x
_
10 kW
0.1 mF
0.1 mF
V_CC–
S0279-01
Figure 34. Offset Nulling Schematic
12
Submit Documentation Feedback
Copyright © 1999–2007, Texas Instruments Incorporated
Product Folder Link(s): THS4021 THS4022