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參數資料
| 型號： | OPA686 |
| 元件分類： | 運動控制電子 |
| 英文描述： | Wideband, Low Noise, Voltage Feedback OPERATIONAL AMPLIFIER |
| 中文描述： | 寬帶，低噪聲，電壓反饋運算放大器 |
| 文件頁數： | 11/15頁 |
| 文件大?。?/td> | 158K |
| 代理商： | OPA686 |
11
OPA686
the primary through to the secondary as a 200
source
impedance and likewise, the 200
R
G
resistor is reflected
through to the transformer primary as a 50
input match-
ing impedance. The noise gain (NG) to the amplifier
output is then 1+ 1000/400 = 3.5V/V. Taking the op amp’s
1.3nV/
√
Hz input voltage noise times this noise gain to the
output, then reflecting this noise term to the input side of
the R
G
resistor, divides it by 5. This gives a net gain of 0.7
for the non-inverting input voltage noise when reflected to
the input point for the op amp circuit. This is further
reduced when referred back to the transformer primary.
The 14dB gain to the matched load for the circuit of Figure
6 is precisely controlled (
±
0.2dB) and gives a 6dB noise
figure at the input of the transformer. The DC noise gain for
this circuit (3.5) is below the specified minimum stable gain.
This will improve the distortion performance at frequencies
below 20MHz from those shown in the Typical Performance
Curves. Adding the inverting compensation capacitors holds
this configuration stable as described in the previous section.
Measured results show 140MHz small-signal bandwidth for
the circuit of Figure 6 with
±
0.1dB flatness through 50MHz.
The OPA686 will easily deliver a 2Vp-p ADC full-scale
input at the matched 50
load. Two-tone testing at 20MHz
for the circuit of Figure 6 (1Vp-p for each test tone) shows
that the two-tone intermodulation intercept has improved to
40dBm versus the 35dBm shown in the Typical Perfor-
mance Curves, giving a 72dBc SFDR for the two 4dBm test
tones at the load .
DESIGN-IN TOOLS
DEMONSTRATION BOARDS
Two PC boards are available to assist in the initial evaluation
of circuit performance using the OPA686 in its two package
styles. Both of these are available free as an unpopulated PC
board delivered with descriptive documentation. The sum-
mary information for these boards is shown in the table
below.
BOARD
PART
NUMBER
LITERATURE
REQUEST
NUMBER
PRODUCT
PACKAGE
OPA686U
OPA686N
8-Pin SO-8
5-Lead SOT23-5
DEM-OPA68xU
DEM-OPA6xxN
MKT-351
MKT-348
Contact the Burr-Brown applications support line to request
any of these boards.
MACROMODELS AND APPLICATIONS SUPPORT
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 induc-
tance can have a major effect on circuit performance. A
SPICE model for the OPA686 is available through either the
Burr-Brown Internet web page (http://www.burr-brown.com)
or as one model on a disk from the Burr-Brown Applications
department (1-800-548-6132). The Applications department
is also available for design assistance at this number. 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 har-
monic distortion characteristics. These models do not at-
tempt to distinguish between the package types in their
small-signal AC performance.
OPERATING SUGGESTIONS
SETTING RESISTOR VALUES TO MINIMIZE NOISE
The OPA686 provides a very low input noise voltage while
requiring a low 12mA quiescent current. To take full advan-
tage of this low input noise, careful attention to the other
possible noise contributors is required. Figure 7 shows the
op amp noise analysis model with all the noise terms
included. In this model, all the noise terms are taken to be
noise voltage or current density terms in either nV/
√
Hz or
pA/
√
Hz.
The total output spot noise voltage can be computed as the
square root of the squared contributing terms to the output
noise voltage. This computation adds all the contributing
noise powers at the output by superposition, then takes the
square root to get back to a spot noise voltage. Equation 1
shows the general form for this output noise voltage using
the terms shown in Figure 7.
Equation 1
(
Dividing this expression by the noise gain (NG = 1+R
F
/R
G
)
will give the equivalent input-referred spot noise voltage at
the non-inverting input as shown in Equation 2.
Equation 2
4kT
R
G
R
G
R
F
R
S
OPA686
I
BI
E
O
I
BN
4kT = 1.6E –20J
at 290°K
E
RS
E
NI
4kTR
S
√
4kTR
F
√
E
O
=
E
NI
2
+
I
BN
R
S
(
)
2
+ 4
kTR
S
)
NG
2
+
I
BI
R
F
(
)
2
+ 4
kTR
F
NG
E
N
=
E
NI
2
+
I
BN
R
S
(
)
2
+ 4
kTR
S
+
I
BI
R
F
NG
2
+4
kTR
F
NG
FIGURE 7. Op Amp Noise Analysis Model.
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| OPA687N | Wideband, Ultra-Low Noise, Voltage Feedback OPERATIONAL AMPLIFIER With Power Down |
| OPA687U | Wideband, Ultra-Low Noise, Voltage Feedback OPERATIONAL AMPLIFIER With Power Down |
| OPA687 | Wideband, Ultra-Low Noise, Voltage Feedback OPERATIONAL AMPLIFIER With Power Down |
| OPA688U | Unity Gain Stable, Wideband VOLTAGE LIMITING AMPLIFIER |
| OPA688P | ECONOLINE: RB & RA - Dual Output from a Single Input Rail- Power Sharing on Output- Industry Standard Pinout- 1kVDC & 2kVDC Isolation- Custom Solutions Available- UL94V-0 Package Material- Efficiency to 85% |
相關代理商/技術參數 |
參數描述 |
|---|---|
| OPA686N | 制造商:BB 制造商全稱:BB 功能描述:Wideband, Low Noise, Voltage Feedback OPERATIONAL AMPLIFIER |
| OPA686N/250 | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Texas Instruments 功能描述: |
| OPA686N/3K | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Texas Instruments 功能描述: |
| OPA686U | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Texas Instruments 功能描述: |
| OPA686U/2K5 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-Feedback Operational Amplifier |
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