THS3202_16 Datasheet, PDF (17/37 Pages) Texas Instruments – 2-GHz, LOW DISTORTION, DUAL CURRENT-FEEDBACK AMPLIFIERS

THS3202
www.ti.com
SLOS242F – SEPTEMBER 2002 – REVISED JANUARY 2010
APPLICATION INFORMATION
INTRODUCTION
The THS3202 is a high-speed, operational amplifier configured in a current-feedback architecture. The device is
built using Texas Instruments BiCOM-II process, a 15-V, dielectrically isolated, complementary bipolar process
with NPN and PNP transistors possessing f_Ts of several GHz. This configuration implements an exceptionally
high-performance amplifier that has a wide bandwidth, high slew rate, fast settling time, and low distortion.
RECOMMENDED FEEDBACK AND GAIN RESISTOR VALUES
As with all current-feedback amplifiers, the bandwidth of the THS3202 is an inversely proportional function of the
value of the feedback resistor. The recommended resistors for the optimum frequency response are shown in
Table 1. These should be used as a starting point and once optimum values are found, 1% tolerance resistors
should be used to maintain frequency response characteristics. For most applications, a feedback resistor value
of 750 Ω is recommended—a good compromise between bandwidth and phase margin that yields a very stable
amplifier.
Table 1. Recommended Resistor Values for Optimum Frequency Response
GAIN
1
2
5
10
–1
THS3202 R_F FOR AC WHEN R_LOAD = 100 Ω
V_SUP
PEAKING
15
Optimum
±5
Optimum
15
Optimum
±5
Optimum
15
Optimum
±5
Optimum
15
Optimum
±5
Optimum
15
Optimum
±5
Optimum
R_F VALUE
619
619
536
536
402
402
200
200
450
450
As shown in Table 1, to maintain the highest bandwidth with an increasing gain, the feedback resistor is reduced.
The advantage of dropping the feedback resistor (and the gain resistor) is that the noise of the system is also
reduced compared to no reduction of these resistor values (see the Noise Calculations section). Thus, keeping
the bandwidth as high as possible maintains very good distortion performance of the amplifier by keeping the
excess loop gain as high as possible.
Care must be taken to not drop these values too low. The amplifier output must drive the feedback resistance
(and gain resistance) and may place a burden on the amplifier. The end result is that distortion may actually
increase due to the low impedance load presented to the amplifier. Careful management of the amplifier
bandwidth and the associated loading effects must be examined by the designer for optimum performance.
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