+VS +IN –IN –V
參數(shù)資料
型號: AD8222HACPZ-R7
廠商: Analog Devices Inc
文件頁數(shù): 7/24頁
文件大?。?/td> 0K
描述: IC AMP INST DUAL PREC LN 16LFCSP
標(biāo)準(zhǔn)包裝: 1
放大器類型: 儀表
電路數(shù): 2
轉(zhuǎn)換速率: 2 V/µs
-3db帶寬: 1.2MHz
電流 - 輸入偏壓: 500pA
電壓 - 輸入偏移: 120µV
電流 - 電源: 900µA
電流 - 輸出 / 通道: 18mA
電壓 - 電源,單路/雙路(±): 4.6 V ~ 36 V,±2.3 V ~ 18 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 16-VQFN,CSP
供應(yīng)商設(shè)備封裝: 16-LFCSP-VQ
包裝: 標(biāo)準(zhǔn)包裝
其它名稱: AD8222HACPZ-R7DKR
AD8222
Rev. A | Page 15 of 24
THEORY OF OPERATION
C1
C2
+VS
+IN
–IN
–VS
10k
400
10k
REF
OUTPUT
IB COMPENSATION
+VS
–VS
+VS
–VS
+VS
VB
II
R1 24.7k
24.7k
RG
Q1
R2
Q2
–VS
+VS
–VS
+VS
A2
A1
A3
05
94
7-
0
45
Figure 44. Simplified Schematic
AMPLIFIER ARCHITECTURE
The two instrumentation amplifiers of the AD8222 are based
on the classic 3-op-amp topology. Figure 44 shows a simplified
schematic of one of the amplifiers. The input transistors, Q1
and Q2, are biased at a fixed current. Any differential input
signal forces the output voltages of A1 and A2 to change so that
the differential voltage also appears across RG. The current that
flows through RG must also flow through R1 and R2, resulting
in a precisely amplified version of the differential input signal
between the outputs of A1 and A2. Topologically, Q1 + A1 + R1
and Q2 + A2 + R2 can be viewed as precision current feedback
amplifiers. The common-mode signal and the amplified differen-
tial signal are applied to a difference amplifier that rejects the
common-mode voltage. The difference amplifier employs innova-
tions that result in low output offset voltage as well as low output
offset voltage drift.
Because the input amplifiers employ a current feedback architec-
ture, the gain-bandwidth product of the AD8222 increases
with gain, resulting in a system that does not suffer from the
expected bandwidth loss of voltage feedback architectures at
higher gains.
The transfer function of the AD8222 is
VOUT = G(V+IN VIN) + VREF
where:
G
R
G
49.4
1
GAIN SELECTION
Placing a resistor across the RG terminals sets the gain of the
AD8222, which can be calculated by referring to Table 8 or by
using the following gain equation:
1
49.4
G
R
G
Table 8. Gains Achieved Using 1% Resistors
1% Standard Table Value of RG (Ω)
Calculated Gain
49.9 k
1.990
12.4 k
4.984
5.49 k
9.998
2.61 k
19.93
1.00 k
50.40
499
100.0
249
199.4
100
495.0
49.9
991.0
The AD8222 defaults to G = 1 when no gain resistor is used.
The tolerance and gain drift of the RG resistor should be added
to the AD8222’s specifications to determine the total gain
accuracy of the system. When the gain resistor is not used,
gain error and gain drift are kept to a minimum.
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