THS3062DGNR Datasheet, PDF (13/33 Pages) Texas Instruments – LOW-DISTORTION, HIGH SLEW RATE, CURRENT-FEEDBACK AMPLIFIERS

THS3061
THS3062
www.ti.com
SLOS394B – JULY 2002 – REVISED NOVEMBER 2009
APPLICATION INFORMATION
INTRODUCTION
The THS306x is a high-speed operational amplifier
configured in a current-feedback architecture. The
device is built using Texas Instruments' BiCOM-I
process, a 30-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.
MAXIMUM SLEW RATE FOR REPETITIVE
SIGNALS
The THS3061 and THS3062 are recommended for
high slew rate, pulsed applications where the internal
nodes of the amplifier have time to stabilize between
pulses.It is recommended to have at least a 20-ns
delay between pulses.
The THS3061 and THS3062 are not recommended
for applications with repetitive signals (sine, square,
sawtooth, or other types) that exceed 900 V/μs. Using
this device in these types of applications results in an
excessive current draw from the power supply and
possible device damage. For applications with a high
slew rate and repetitive signals, the THS3091 and
THS3095 (singles) or the THS3092 and THS3096
(duals) are recommended instead.
RECOMMENDED FEEDBACK AND GAIN
RESISTOR VALUES
As with all current-feedback amplifiers, the bandwidth
of the THS306x is an inversely proportional function
of the value of the feedback resistor. The
recommended resistors for 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.
As shown in Table 1, to maintain the highest
bandwidth with increasing gain, the feedback resistor
is reduced. The advantage of dropping the feedback
resistance (and the gain-resistor value) is that the
noise of the system is also reduced compared to no
reduction of these resistor values (see NOISE
CALCULATIONS). 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.
Table 1. Recommended Resistor Values for
Optimum Frequency Response
GAIN
1
2, –1
5
10
R_F for V_CC = ±15 V
750 Ω
560 Ω
357 Ω
200 Ω
R_F for V_CC = ±5 V
750 Ω
560 Ω
383 Ω
200 Ω
Care must be taken to not set these values too low.
The amplifier's output must drive the feedback
resistance (and gain resistance), and this 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. The
designer must carefully manage the amplifier
bandwidth and the associated loading effects for
optimum performance.
The THS3061/62 amplifiers exhibit very good
distortion performance and bandwidth, and can use
power supplies up to 15 V. The excellent
current-drive capability of up to 145 mA into a 50-Ω
load allows many versatile applications. One
application is driving a twisted pair line (that is, a
telephone line). Figure 48 shows a simple circuit for
driving a twisted pair differentially.
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Product Folder Link(s): THS3061 THS3062
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