THS3201-EP_14 Datasheet, PDF (18/34 Pages) Texas Instruments – 1.8-GHz LOW-DISTORTION CURRENT-FEEDBACK AMPLIFIER

THS3201-EP
SGLS283B – APRIL 2005 – REVISED JANUARY 2009 ..................................................................................................................................................... www.ti.com
APPLICATION INFORMATION
Wideband Noninverting Operation
The THS3201 is a unity gain stable 1.8-GHz
current-feedback operational amplifier, designed to
operate from a ±3.3-V to ±7.5-V power supply.
Figure 56 shows the THS3201 in a noninverting gain
of 2-V/V configuration typically used to generate the
performance curves. Most of the curves are
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 56 matches the
source impedance of the test generator.
7.5 V _+VS
50 Ω Source
V_I
49.9 Ω
768 Ω
100 pF
0.1 µF
+
6.8 µF
+
THS3201
_
R_F
49.9 Ω
50 Ω
768 Ω
R_G
0.1 µF 6.8 µF
100 pF
+
-7.5 V ^-VS
Figure 56. 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.
Table 1. Recommended Resistor Values for
Optimum Frequency Response
Gain
(V/V)
1
2
5
10
–1
–2
–5
–10
THS3201 R_F for AC When R_load = 100 Ω
Supply Voltage
R_G
R_F
(V)
(Ω)
(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 57 shows the THS3201 is a typical inverting
gain configuration, where the input and output
impedances and signal gain from Figure 56 are
retained in an inverting circuit configuration.
7.5 V _+VS
50 Ω Source _RG
V_I
287 Ω
R_M
60.4 Ω
100 pF
0.1 µF
+
6.8 µF
+
THS3201
_
49.9 Ω
50 Ω
R_F
576 Ω
0.1 µF 6.8 µF
100 pF
+
-7.5 V ^-VS
Figure 57. Wideband Inverting Gain Configuration
18
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