- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄375234 > AD625 (Analog Devices, Inc.) Programmable Gain Instrumentation Amplifier(儀器用放大器) PDF資料下載
參數(shù)資料
| 型號(hào)： | AD625 |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | 運(yùn)動(dòng)控制電子 |
| 英文描述： | Programmable Gain Instrumentation Amplifier(儀器用放大器) |
| 中文描述： | 可編程增益儀表放大器（儀器用放大器） |
| 文件頁數(shù)： | 7/14頁 |
| 文件大?。?/td> | 549K |
| 代理商： | AD625 |
AD625
REV. B
–7–
Theory of Operation
The AD625 is a monolithic instrumentation amplifier based on
a modification of the classic three-op-amp approach. Mono-
lithic construction and laser-wafer-trimming allow the tight
matching and tracking of circuit components. This insures the
high level of performance inherent in this circuit architecture.
A preamp section (Q1–Q4) provides additional gain to A1 and
A2. Feedback from the outputs of A1 and A2 forces the collec-
tor currents of Q1–Q4 to be constant, thereby, impressing the
input voltage across R
G
. This creates a differential voltage at the
outputs of A1 and A2 which is given by the gain (2R
F
/R
G
+ 1)
times the differential portion of the input voltage. The unity
gain subtracter, A3, removes any common-mode signal from
the output voltage yielding a single ended output, V
OUT
, referred
to the potential at the reference pin.
The value of R
G
is the determining factor of the transconduc-
tance of the input preamp stage. As R
G
is reduced for larger
gains the transconductance increases. This has three important
advantages. First, this approach allows the circuit to achieve a
very high open-loop gain of (3
×
10
8
at programmed gains
≥
500)
thus reducing gain related errors. Second, the gain-bandwidth
product, which is determined by C3, C4, and the input trans-
conductance, increases with gain, thereby, optimizing frequency
response. Third, the input voltage noise is reduced to a value
determined by the collector current of the input transistors
(4 nV/
√
Hz
).
INPUT PROTECTION
Differential input amplifiers frequently encounter input voltages
outside of their linear range of operation. There are two consid-
erations when applying input protection for the AD625; 1) that
continuous input current must be limited to less than 10 mA
and 2) that input voltages must not exceed either supply by
more than one diode drop (approximately 0.6 V @ 25
°
C).
Under differential overload conditions there is (R
G
+ 100)
in
series with two diode drops (approximately 1.2 V) between the
plus and minus inputs, in either direction. With no external pro-
tection and R
G
very small (i.e., 40
), the maximum overload
voltage the AD625 can withstand, continuously, is approximately
±
2.5 V. Figure 26a shows the external components necessary to
protect the AD625 under all overload conditions at any gain.
Figure 25. Simplified Circuit of the AD625
The diodes to the supplies are only necessary if input voltages
outside of the range of the supplies are encountered. In higher
gain applications where differential voltages are small, back-to-
back Zener diodes and smaller resistors, as shown in Figure
26b, provides adequate protection. Figure 26c shows low cost
FETs with a maximum ON resistance of 300
configured to
offer input protection with minimal degradation to noise, (5.2
nV/
√
Hz
compared to normal noise performance of 4 nV/
√
Hz
).
During differential overload conditions, excess current will flow
through the gain sense lines (Pins 2 and 15). This will have no
effect in fixed gain applications. However, if the AD625 is being
used in an SPGA application with a CMOS multiplexer, this
current should be taken into consideration. The current capa-
bilities of the multiplexer may be the limiting factor in allowable
overflow current. The ON resistance of the switch should be in-
cluded as part of R
G
when calculating the necessary input pro-
tection resistance.
Figure 26a. Input Protection Circuit
Figure 26b. Input Protection Circuit for G>5
Figure 26c. Input Protection Circuit
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AD628ARMZ | High Common-Mode Voltage, Programmable Gain Difference Amplifier |
| AD628ARMZ-R7 | High Common-Mode Voltage, Programmable Gain Difference Amplifier |
| AD628ARMZ-RL | High Common-Mode Voltage, Programmable Gain Difference Amplifier |
| AD628ARZ | High Common-Mode Voltage, Programmable Gain Difference Amplifier |
| AD628ARZ-R7 | High Common-Mode Voltage, Programmable Gain Difference Amplifier |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD62501P | 制造商:TOSHIBA 制造商全稱:Toshiba Semiconductor 功能描述:7 SINGLE DRIVER |
| AD62550A | 制造商:ESMT 制造商全稱:Elite Semiconductor Memory Technology Inc. 功能描述:Class-D Audio Power Amplifier with USB / I2S Interface |
| AD62551A | 制造商:ESMT 制造商全稱:Elite Semiconductor Memory Technology Inc. 功能描述:USB controller with external Amplifier and Recording function |
| AD6255A | 制造商:ESMT 制造商全稱:Elite Semiconductor Memory Technology Inc. 功能描述:Class-D Audio Power Amplifier with USB / I2S Interface and Recording function |
| AD625A | 制造商:AD 制造商全稱:Analog Devices 功能描述:Programmable Gain Instrumentation Amplifier |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。