Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF Download HTML

OPA2690 Datasheet(PDF) 19 Page - Burr-Brown (TI)

[Old version datasheet] Texas Instruments acquired Burr-Brown Corporation. Click here to check the latest version.
Part No. OPA2690
Description  Dual, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable
Download  30 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  BURR-BROWN [Burr-Brown (TI)]
Homepage  http://www.burr-brown.com
Logo 

OPA2690 Datasheet(HTML) 19 Page - Burr-Brown (TI)

Zoom Inzoom in Zoom Outzoom out
 19 / 30 page
background image
OPA2690
SBOS238D − JUNE 2002 − REVISED DECEMBER 2004
www.ti.com
19
MACROMODELS
Computer simulation of circuit performance using SPICE
is often useful when analyzing the performance of analog
circuits and systems. This is particularly true for video and
RF amplifier circuits where parasitic capacitance and
inductance can have a major effect on circuit performance.
A SPICE model for the OPA2690 (use two OPA690 SPICE
models) is available through the Texas Instruments web
page (http://www.ti.com). These models do a good job of
predicting small-signal AC and transient performance
under a wide variety of operating conditions. They do not
do as well in predicting the harmonic distortion or dG/dP
characteristics.
These
models
do
not
attempt
to
distinguish
between
the
package
types
in
their
small-signal AC performance.
OPERATING SUGGESTIONS
OPTIMIZING RESISTOR VALUES
As the OPA2690 is a unity-gain stable, voltage-feedback
op amp, a wide range of resistor values may be used for
the feedback and gain setting resistors. The primary limits
on these values are set by dynamic range (noise and
distortion) and parasitic capacitance considerations. For a
noninverting unity-gain follower application, the feedback
connection should be made with a 25
Ω resistor, not a
direct
short.
This
will
isolate
the
inverting
input
capacitance from the output pin and improve the
frequency response flatness. Usually, the feedback
resistor value should be between 200
Ω and 1.5kΩ. Below
200
Ω, the feedback network will present additional output
loading which can degrade the harmonic distortion
performance of the OPA2690. Above 1.5k
Ω, the typical
parasitic capacitance (approximately 0.2pF) across the
feedback resistor can cause unintentional band-limiting in
the amplifier response.
A good rule of thumb is to target the parallel combination
of RF and RG (see Figure 1) to be less than approximately
300
Ω. The combined impedance RF RG interacts with
the inverting input capacitance, placing an additional pole
in the feedback network and thus, a zero in the forward
response. Assuming a 2pF total parasitic on the inverting
node, holding RF RG < 300Ω will keep this pole above
250MHz. By itself, this constraint implies that the feedback
resistor RF can increase to several kΩ at high gains. This
is acceptable as long as the pole formed by RF and any
parasitic capacitance appearing in parallel is kept out of
the frequency range of interest.
BANDWIDTH vs GAIN: NONINVERTING
OPERATION
Voltage-feedback op amps exhibit decreasing closed-loop
bandwidth as the signal gain is increased. In theory, this
relationship is described by the Gain Bandwidth Product
(GBP) shown in the Electrical Characteristics. Ideally,
dividing GBP by the noninverting signal gain (also called
the Noise Gain, or NG) will predict the closed-loop
bandwidth. In practice, this only holds true when the phase
margin approaches 90
°, as it does in high gain
configurations. At low gains (increased feedback factors),
most amplifiers will exhibit a more complex response with
lower phase margin. The OPA2690 is compensated to
give a slightly peaked response in a noninverting gain of
2 (see Figure 1). This results in a typical gain of +2
bandwidth of 220MHz, far exceeding that predicted by
dividing the 300MHz GBP by 2. Increasing the gain will
cause the phase margin to approach 90
° and the
bandwidth to more closely approach the predicted value of
(GBP/NG). At a gain of +10, the 30MHz bandwidth shown
in the Electrical Characteristics agrees with that predicted
using the simple formula and the typical GBP of 300MHz.
The frequency response in a gain of +2 may be modified
to achieve exceptional flatness simply by increasing the
noise gain to 2.5. One way to do this, without affecting the
+2 signal gain, is to add an 804
Ω resistor across the two
inputs in the circuit of Figure 1. A similar technique may be
used to reduce peaking in unity-gain (voltage follower)
applications. For example, by using a 402
Ω feedback
resistor along with a 402
Ω resistor across the two op amp
inputs, the voltage follower response will be similar to the
gain of +2 response of Figure 2. Reducing the value of the
resistor across the op amp inputs will further limit the
frequency response due to increased noise gain.
The OPA2690 exhibits minimal bandwidth reduction going
to single-supply (+5V) operation as compared with
±5V.
This is because the internal bias control circuitry retains
nearly constant quiescent current as the total supply
voltage between the supply pins is changed.
INVERTING AMPLIFIER OPERATION
Since the OPA2690 is a general-purpose, wideband
voltage-feedback op amp, all of the familiar op amp
application circuits are available to the designer. Inverting
operation is one of the more common requirements and
offers several performance benefits. See Figure 12 for a
typical inverting configuration where the I/O impedances
and signal gain from Figure 1 are retained in an inverting
circuit configuration.
In
the
inverting
configuration,
three
key
design
considerations must be noted. The first is that the gain
resistor (RG) becomes part of the signal channel input
impedance. If input impedance matching is desired (which
is beneficial whenever the signal is coupled through a
cable, twisted-pair, long PC board trace, or other
transmission line conductor), RG may be set equal to the
required termination value and RF adjusted to give the
desired gain. This is the simplest approach and results in
optimum bandwidth and noise performance. However, at
low inverting gains, the resultant feedback resistor value
can present a significant load to the amplifier output. For
an inverting gain of −2, setting RG to 50Ω for input
matching eliminates the need for RM but requires a 100Ω


Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30 


Datasheet Download




Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Alldatasheet API   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn