THS3201 Datasheet, PDF (14/29 Pages) Texas Instruments – 1.8-GHz, LOW DISTORTION, CURRENT FEEDBACK AMPLIFIER

THS3201
SLOS416A − JUNE 2003 − REVISED JANUARY 2004
www.ti.com
APPLICATION INFORMATION
WIDEBAND, NONINVERTING OPERATION
Table 1. Recommended Resistor Values for
Optimum Frequency Response
The THS3201 is a unity gain stable 1.8-GHz
current-feedback operational amplifiers, designed to
operate from a ±3.3-V to ±7.5-V power supply.
Figure 50 shows the THS3201 in a noninverting gain of
2V/V configuration typically used to generate the
performance curves. Most of the curves were
characterized using signal sources with 50-Ω source
impedance, and with measurement equipment presenting
a 50-Ω load impedance. The 49.9-Ω shunt resistor at the
V_I terminal in Figure 50 matches the source impedance of
the test generator.
7.5 V _+VS
50 Ω Source
VI
49.9 Ω
768 Ω
100 pF
0.1 µF
+
6.8 µF
+
THS3201
_
RF
768 Ω
RG
100 pF
49.9 Ω
0.1 µF
50 Ω
6.8 µF
+
−7.5 V ^−VS
Gain
(V/V)
1
2
5
10
−1
−2
−5
−10
THS3201 RF for AC When Rload = 100 Ω
Supply Voltage
(V)
RG (Ω)
RF (Ω)
±7.5
—
1.2 k
±5
—
1.2 k
±7.5
768
768
±5
715
715
±7.5
154.9
619
±5
143
576
±7.5
54.9
487
±5
51.1
464
±7.5
619
619
±5
576
576
±7.5 and ±5
287
576
±7.5 and ±5
110
549
±7.5 and ±5
49.9
499
WIDEBAND, INVERTING GAIN OPERATION
Figure 51 shows the THS3201 is a typical inverting gain
configuration where the input and output impedances and
signal gain from Figure 50 are retained in an inverting
circuit configuration.
7.5 V _+VS
100 pF
0.1 µF
+
6.8 µF
Figure 50. Wideband, Noninverting Gain
Configuration
Unlike voltage-feedback amplifiers, current-feedback
amplifiers are highly dependent on the feedback resistor
R_F for maximum performance and stability. Table 1 shows
the optimal gain setting resistors R_F and R_G at different
gains to give maximum bandwidth with minimal peaking in
the frequency response. Higher bandwidths can be
achieved, at the expense of added peaking in the
frequency response, by using even lower values for R_F.
Conversely, increasing R_F decreases the bandwidth, but
stability is improved.
50 Ω Source _RG
VI
287 Ω
RM
60.4 Ω
+
THS3201
_
49.9 Ω
50 Ω
RF
576 Ω
100 pF
0.1 µF
6.8 µF
+
−7.5 V ^−VS
Figure 51. Wideband, Inverting Gain
Configuration
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