Datasheet

APPLICATION INFORMATION
Wideband, Noninverting Operation
OPA659
R
OUT
0.1 Fm 10 Fm
0.1 Fm 10 Fm
50 LoadW
50 SourceW
R
T
R
G
V
IN
V
OUT
R
F
+6V
-6V
OPA659
R
OUT
0.1 Fm 10 Fm
0.1 Fm 10 Fm
50 LoadW
50 SourceW
R
T
V
IN
V
OUT
+6V
-6V
OPA659
SBOS342B – DECEMBER 2008 – REVISED AUGUST 2009 ............................................................................................................................................ www.ti.com
Voltage-feedback op amps can use a wide range of
resistor values to set the gain. To retain a controlled
The OPA659 is a very broadband, unity-gain stable,
frequency response for the noninverting voltage
voltage-feedback amplifier with a high impedance
amplifier of Figure 35 , the parallel combination of R
F
JFET-input stage. Its very high gain bandwidth
|| R
G
should always be less than 200 Ω . In the
product (GBP) of 350MHz can be used to either
noninverting configuration, the parallel combination of
deliver high signal bandwidths for low-gain buffers, or
R
F
|| R
G
forms a pole with the parasitic input and
to deliver broadband, low-noise, transimpedance
board layout capacitance at the inverting input of the
bandwidth to photodiode-detector applications. The
OPA659. For best performance, this pole should be
OPA659 is designed to to provide very low distortion
at a frequency greater than the closed-loop
and accurate pulse response with low overshoot and
bandwidth for the OPA659. For this reason, a direct
ringing. To achieve the full performance of the
short from the output to the inverting input is
OPA659, careful attention to printed circuit board
recommended for the unity-gain follower application.
(PCB) layout and component selection are required,
Table 1 lists several recommended resistor values for
as discussed in the remaining sections of this data
noninverting gains with a 50 Ω input/output match.
sheet.
Figure 34 shows the noninverting gain of +1 circuit;
Figure 35 shows the more general circuit used for
other noninverting gains. These circuits are used as
the basis for most of the noninverting gain Typical
Characteristics graphs. Most of the graphs were
characterized using signal sources with 50 Ω driving
impedance, and with measurement equipment
presenting a 50 Ω load impedance. In Figure 34 , the
shunt resistor R
T
at V
IN
should be set to 50 Ω to
match the source impedance of the test generator
and cable, while the series output resistor, R
OUT
, at
V
OUT
should also be set to 50 Ω to provide matching
impedance for the measurement equipment load and
cable. Generally, data sheet voltage swing
Figure 35. General Noninverting Test Circuit
specifications are measured at the output pin, V
OUT
,
in Figure 34 and Figure 35 .
Table 1. Resistor Values for Noninverting Gains
with 50 Ω Input/Output Match
NONINVERTING
GAIN R
F
R
G
R
T
R
OUT
+1 0 Open 49.9 49.9
+2 249 249 49.9 49.9
+5 249 61.9 49.9 49.9
+10 249 27.4 49.9 49.9
Figure 34. Noninverting Gain of +1 Test Circuit
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