Datasheet

THS3061
THS3062
www.ti.com SLOS394B –JULY 2002–REVISED NOVEMBER 2009
APPLICATION INFORMATION
maintain frequency response characteristics. For
most applications, a feedback-resistor value of 750 Ω
INTRODUCTION
is recommended—a good compromise between
The THS306x is a high-speed operational amplifier
bandwidth and phase margin that yields a very stable
configured in a current-feedback architecture. The
amplifier.
device is built using Texas Instruments' BiCOM-I
As shown in Table 1, to maintain the highest
process, a 30-V, dielectrically isolated,
bandwidth with increasing gain, the feedback resistor
complementary bipolar process with NPN and PNP
is reduced. The advantage of dropping the feedback
transistors possessing f
T
s of several GHz. This
resistance (and the gain-resistor value) is that the
configuration implements an exceptionally
noise of the system is also reduced compared to no
high-performance amplifier that has a wide
reduction of these resistor values (see NOISE
bandwidth, high slew rate, fast settling time, and low
CALCULATIONS). Thus, keeping the bandwidth as
distortion.
high as possible maintains very good distortion
performance of the amplifier by keeping the excess
MAXIMUM SLEW RATE FOR REPETITIVE
loop gain as high as possible.
SIGNALS
The THS3061 and THS3062 are recommended for
Table 1. Recommended Resistor Values for
high slew rate, pulsed applications where the internal
Optimum Frequency Response
nodes of the amplifier have time to stabilize between
GAIN R
F
for V
CC
= ±15 V R
F
for V
CC
= ±5 V
pulses.It is recommended to have at least a 20-ns
1 750 Ω 750 Ω
delay between pulses.
2, –1 560 Ω 560 Ω
The THS3061 and THS3062 are not recommended
5 357 Ω 383 Ω
for applications with repetitive signals (sine, square,
10 200 Ω 200 Ω
sawtooth, or other types) that exceed 900 V/μs. Using
this device in these types of applications results in an
Care must be taken to not set these values too low.
excessive current draw from the power supply and
The amplifier's output must drive the feedback
possible device damage. For applications with a high
resistance (and gain resistance), and this may place
slew rate and repetitive signals, the THS3091 and
a burden on the amplifier. The end result is that
THS3095 (singles) or the THS3092 and THS3096
distortion may actually increase due to the
(duals) are recommended instead.
low-impedance load presented to the amplifier. The
designer must carefully manage the amplifier
RECOMMENDED FEEDBACK AND GAIN
bandwidth and the associated loading effects for
RESISTOR VALUES
optimum performance.
As with all current-feedback amplifiers, the bandwidth
The THS3061/62 amplifiers exhibit very good
of the THS306x is an inversely proportional function
distortion performance and bandwidth, and can use
of the value of the feedback resistor. The
power supplies up to 15 V. The excellent
recommended resistors for optimum frequency
current-drive capability of up to 145 mA into a 50-Ω
response are shown in Table 1. These should be
load allows many versatile applications. One
used as a starting point, and once optimum values
application is driving a twisted pair line (that is, a
are found, 1% tolerance resistors should be used to
telephone line). Figure 48 shows a simple circuit for
driving a twisted pair differentially.
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