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參數資料
| 型號： | AD8571 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
| 中文描述： | 零漂移，單電源，軌到軌輸入/輸出運算放大器 |
| 文件頁數： | 12/19頁 |
| 文件大小： | 247K |
| 代理商： | AD8571 |
AD8571/AD8572/AD8574
–12–
REV. 0
V
OUT
V
IN
AD8572
V
OUT
V
IN
AD8572
V
OUT
V
IN
AD8572
Figure 46. Guard Ring Layout and Connections to Reduce
PC Board Leakage Currents
V
2
V+
V
REF
V
IN1
V
IN2
GUARD
RING
R
2
R
2
R
1
R
1
AD8572
V
REF
GUARD
RING
Figure 47. Top View of AD8572 SOIC Layout with
Guard Rings
Other potential sources of offset error are thermoelectric voltages
on the circuit board. This voltage, also called Seebeck voltage,
occurs at the junction of two dissimilar metals and is proportional
to the temperature of the junction. The most common metallic
junctions on a circuit board are solder-to-board trace and solder-
to-component lead. Figure 48 shows a cross-section diagram view
of the thermal voltage error sources. If the temperature of the PC
board at one end of the component (T
A1
) is different from the
temperature at the other end (T
A2
), the Seebeck voltages will not
be equal, resulting in a thermal voltage error.
This thermocouple error can be reduced by using dummy com-
ponents to match the thermoelectric error source. Placing the
dummy component as close as possible to its partner will ensure
both Seebeck voltages are equal, thus canceling the thermo-
couple error. Maintaining a constant ambient temperature on
the circuit board will further reduce this error. The use of a
ground plane will help distribute heat throughout the board and
will also reduce EMI noise pickup.
SURFACE MOUNT
COMPONENT
COMPONENT
LEAD
SOLDER
PC BOARD
COPPER
TRACE
V
SC2
2
+
+
2
V
TS2
T
A2
T
A1
V
SC1
2
+
+
2
V
TS1
IF T
A1
=
T
A2
, THEN
V
TS1
+ V
SC1
=
V
TS2
+ V
SC2
Figure 48. Mismatch in Seebeck Voltages Causes a
Thermoelectric Voltage Error
V
OUT
V
IN
AD857x
A
V
= 1 + (R
F
/R
1
)
R
1
R
F
R
S
= R
1
NOTE: R
SHOULD BE PLACED IN CLOSE PROXIMITY AND
ALIGNMENT TO R
1
TO BALANCE SEEBECK VOLTAGES
Figure 49. Using Dummy Components to Cancel
Thermoelectric Voltage Errors
1/f Noise Characteristics
Another advantage of autozero amplifiers is their ability to cancel
flicker noise. Flicker noise, also known as 1/f noise, is noise inher-
ent in the physics of semiconductor devices and increases 3 dB
for every octave decrease in frequency. The 1/f corner frequency
of an amplifier is the frequency at which the flicker noise is equal
to the broadband noise of the amplifier. At lower frequencies,
flicker noise dominates, causing higher degrees of error for sub-
Hertz frequencies or dc precision applications.
Because the AD857x amplifiers are self-correcting op amps,
they do not have increasing flicker noise at lower frequencies.
In essence, low frequency noise is treated as a slowly varying
offset error and is greatly reduced as a result of autocorrection.
The correction becomes more effective as the noise frequency
approaches dc, offsetting the tendency of the noise to increase
exponentially as frequency decreases. This allows the AD857x
to have lower noise near dc than standard low-noise amplifiers
that are susceptible to 1/f noise.
Random Autozero Correction Eliminates Intermodulation
Distortion
The AD857x can be used as a conventional op amp for gains up
to 1 MHz. The autozero correction frequency of the device
continuously varies, based on a pseudo-random generator with a
uniform distribution from 2 kHz to 4 kHz. The randomization
of the autocorrection clock creates a continuous randomization
of intermodulation distortion (IMD) products, which show up
as simple broadband noise at the output of the amplifier. This
noise naturally combines with the amplifier’s voltage noise in a
root-squared-sum fashion, resulting in an output free of IMD.
Figure 50a shows the spectral output of an AD8572 with the
amplifier configured for unity gain and the input grounded. Figure
50b shows the spectral output with the amplifier configured for a
gain of 60 dB.
相關PDF資料 |
PDF描述 |
|---|---|
| AD8572 | Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
| AD8572AR | Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
| AD8572ARU | Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
| AD8574 | Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
| AD8574AR | Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD8571_06 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
| AD8571_07 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
| AD8571AR | 制造商:Analog Devices 功能描述:SP Amp Chopper Stabilization Single R-R I/O 5V 8-Pin SOIC N Tube 制造商:Rochester Electronics LLC 功能描述:SINGLE PRECISION RAIL-RAIL CHOPPER OPAMP - Bulk 制造商:Analog Devices 功能描述:OP AMP Z-DRIFT RRI/O 8571 SOIC8 |
| AD8571AR | 制造商:Analog Devices 功能描述:IC SM OP-AMP Z-DRIFT RRI/O ((NW)) |
| AD8571ARM | 制造商:AD 制造商全稱:Analog Devices 功能描述:Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifiers |
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