THS3201 Datasheet, PDF (15/29 Pages) Texas Instruments – 1.8-GHz, LOW DISTORTION, CURRENT FEEDBACK AMPLIFIER

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SINGLE SUPPLY OPERATION
The THS3201 has the capability to operate from a single
supply voltage ranging from 6.6V to 15V. When operating
from a single power supply, care must be taken to ensure
the input signal and amplifier is biased appropriately to
allow for the maximum output voltage swing. The circuits
shown in Figure 52 demonstrate methods to configure an
amplifier in a manner conducive for single supply
operation
+VS
50 Ω Source
VI
RT 49.9 Ω
+
THS3201
_
+VS
2
RF
RG
768 Ω
768 Ω
+VS
2
50 Ω Source
RG
VI
287 Ω
60.4 Ω RT
+VS
+VS
2
2
RF
576 Ω
VS
_
THS3201
+
49.9 Ω
50 Ω
49.9 Ω
50 Ω
Figure 52. DC-Coupled Single Supply Operation
VIDEO AND HDTV DRIVERS
The exceptional bandwidth and slew rate of the THS3201
matches the demands for professional video and HDTV.
Most commercial HDTV standards requires a video
passband of 30-MHz. To ensure high signal quality with
minimal degradation of performance, a 0.1-dB gain
flatness should be at least 7x the passband frequency to
minimize group delay variations—requiring 210-MHz
0.1-dB frequency flatness from the amplifier. High slew
rates ensures there is minimal distortion of the video
signal. Component video and RGB video signals require
fast transition times and fast settling times to keep a high
signal quality. The THS8135, for example, is a 240 MSPS
video DAC and has a transition time approaching 4-ns.
The THS3201 is a perfect candidate for interfacing the
output of such high-performance video components.
THS3201
SLOS416A − JUNE 2003 − REVISED JANUARY 2004
768 Ω
768 Ω
±7.5 V
VI
THS3201
−
+
75-Ω Transmission Line
75 Ω
VO(1)
±7.5 V
75 Ω
n Lines
75 Ω
75 Ω
VO(n)
75 Ω
Figure 53. Video Distribution Amplifier
Application
ADC DRIVER APPLICATION
The THS3201 can be used as a high-performance ADC
driver in applications like radio receiver IF stages, and test
and measurement devices. All high-performance ADCs
have differential inputs. The THS3201 can be used in
conjunction with a transformer as a drive amplifier in these
applications. Figure 54 and Figure 55 show two different
approaches.
In Figure 54, a transformer is used after the amplifier to
convert the signal to differential. The advantage of this
approach is fewer components are required. R_OUT and R_T
are required for impedance matching the transformer.
VS+
0.1 µF
RG
RF
THS3201
ROUT 1:n
24.9 Ω
VIN
RT 47pF
ADC
24.9 Ω
VS−
CM
47pF
0.1 µF
0.1 µF
Figure 54. Differential ADC Driver Circuit 1
In Figure 55, a transformer is used before two amplifiers to
convert the signal to differential. The two amplifiers then
amplify the differential signal. The advantage to this
approach is each amplifier is required to drive half the
voltage as before. R_T is used to impedance match the
transformer.
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