Datasheet

OPA653
V
OUT
V
IN-
V
IN+
160 W
49.9 W
160 W
72.3 W
49.9 W
0.1 Fm 10 Fm
0.1 Fm 10 Fm
+6V
-6V
50-W
Load
50-W
Source
V
S+
V
S-
OPA653
V
OUT
V
IN-
V
IN+
160 W
49.9 W
160 W
49.9 W
0.1 Fm 10 Fm
0.1 Fm 10 Fm
+6V
-6V
50-W
Load
50-W
Source
V
S+
V
S-
OPA653
www.ti.com SBOS348A –DECEMBER 2008–REVISED NOVEMBER 2009
APPLICATION INFORMATION
Figure 22 shows the OPA653 in an inverting gain of
Wideband, Noninverting, and Inverting
–1 V/V configuration in a 50-Ω test environment as
Operation
was used for testing the Typical Characteristics. The
circuit operation is essentially the same as Figure 21
The OPA653 is a very broadband, voltage-feedback
except that a 72.3-Ω termination resistor is now used
amplifier with internal gain-setting resistors that set a
between the V
IN–
input and ground, so that together
fixed gain of +2 V/V or -1 V/V and a high-impedance
with the gain-setting resistor (R
G
= 160 Ω), the input
JFET-input stage. Its very high bandwidth of 500 MHz
impedance is approximately 50 Ω. The V
IN+
input is
can be used to either deliver high signal bandwidths
terminated to ground using a 49.9-Ω resistor as a
at a gain of +2 V/V or, if driven from a low-impedance
precaution to avoid single transistor oscillations at the
source, a gain of –1 V/V . The OPA653 is designed to
input; the value is not critical, but attention should be
provide very low noise and accurate pulse response
paid to avoid large values because of the noise
with low overshoot and ringing. To achieve the full
contribution as noted below.
performance of the OPA653, careful attention to
printed circuit board (PCB) layout and component
selection is required as discussed in the remaining
sections of this data sheet.
Figure 21 shows the noninverting gain of +2-V/V
circuit that is used as the basis for the Typical
Characteristics. Most of the curves were
characterized using signal sources with 50-Ω driving
impedance, and with measurement equipment that
presents a 50-Ω load impedance. In Figure 21, the
49.9-Ω shunt resistor to ground at the V
IN+
input is
used to match the source impedance of the test
generator and cable, while the 49.9-Ω series output
resistor V
OUT
provides matching impedance for the
measurement equipment load and cable. Data sheet
voltage swing specifications are taken at the
Figure 22. Inverting Gain of –1 V/V in 50-Ω Test
noninverting input pin, V
IN+
, or the output pin, V
OUT
,
Environment
unless otherwise noted.
Note that the 72.3-Ω input termination resistor and
the 50-Ω source impedance of the test equipment
modify the noise gain to +1.84 V/V and the amplifier
is compensated for optimal performance with a noise
gain of +2 V/V. This compensation reduces the phase
margin and results in more peaking in the frequency
response and more overshoot/ringing in the pulse
response. This effect can be seen by comparing the
inverting and noninverting frequency and pulse
response graphs in the characteristic data. The
amplifier phase margin can be restored in an
application that uses an inverting configuration if it is
driven from a very low impedance source such as an
op amp.
Figure 21. Noninverting Gain of +2 V/V in 50-Ω
Test Environment
space
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