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参数资料
| 型号： | AD8225 |
| 厂商： | Analog Devices, Inc. |
| 元件分类： | 运动控制电子 |
| 英文描述： | Precision Gain of 5 Instrumentation Amplifier |
| 中文描述： | 5精密增益仪表放大器 |
| 文件页数： | 12/16页 |
| 文件大小： | 372K |
| 代理商： | AD8225 |
REV. A
–12–
AD8225
Driving a High Resolution ADC
Most high precision ADCs feature differential analog inputs.
Differential inputs offer an inherent 6 dB improvement in S/N
ratio and resultant bit resolution. These advantages are easy to
realize using a pair of AD8225s.
AD8225s can be configured to drive an ADC with differential
inputs by using either single-ended or differential inputs to the
AD8225s. Figure 7 shows the circuit connections for a differen-
tial input. A single-ended input may be configured by connecting
the negative input terminal to ground.
2
3
2
3
6
6
5
5
AD8225
AD8225
OP177
1.25V
4.99k
4.99k
2.7nF
2.7nF
75
75
AD7675
100kSPS
5V
1
AD780
2.5V
RERERENCE
+IN
–IN
ALTERNATE
CONNECTION
FOR SE SOURCE
Figure 7. Driver for Differential ADC
The AD7675 ADC illustrated in Figure 7 is a SAR type converter.
When the input is sampled, the internal sample-and-hold capacitor
is charged to the input voltage level. Since the output of the
AD8225 cannot track the instantaneous current surge, a voltage
glitch develops. To source the momentary current surge, a
capacitor is connected from the A/D input terminal to ground.
Since the AD8225 cannot tolerate greater than approximately
100 pF of capacitance at its output, a 75
series resistor is
required at each in amp output to prevent oscillation.
Using the Reference Input
Note in the example in Figure 7 that Pin 5, the reference input, is
driven by a voltage source. This is because the reference pin is
internally connected to a 15 k
resistor, which is carefully trimmed
to optimize common-mode rejection. Any additional resistance
connected to this node will unbalance the bridge network formed
by the two 3 k
and two 15 k
resistors, resulting in an error
voltage generated by common-mode voltages at the input pins.
AD8225 Used as an EKG Front End
The topology of the instrumentation amplifier has made it the
circuit configuration of choice for designers of EKG and other
low level biomedical amplifiers. CMRR and common-mode
voltage advantages of the instrumentation amplifier are tailor
made to meet the challenges of detecting minuscule cardiac
generated voltage levels in the presence of overwhelming levels
of noise and dc offset voltage. The subtracter circuit of the in
amp will extract and amplify low level signals that are virtually
obscured by the presence of high common-mode dc and ac
potentials.
A typical circuit block diagram of an EKG amplifier is shown in
Figure 8. Using discrete op amps in the in amp and gain stages,
the signal chain usually includes several filters, high voltage
protection, lead-select circuitry, patient lead buffering, and an
ADC. Designers who roll their own instrumentation amplifiers
must provide precision custom trimmed resistor networks and
well matched op amps.
The AD8225 instrumentation amplifier not only replaces all the
components shown in the highlighted block in Figure 8, but also
provides a solution to many of the difficult design problems
encountered in EKG front ends. Among these are patient gener-
ated errors from ac noise sources and errors generated by unequal
electrode potentials. Alone, these error voltages can exceed the
desired QRS complex by orders of magnitude.
INSTRUMENTATION AMPLIFIER
G = 3 TO 10
LEAD
SELECT,
HV
PROTECTION,
FILTERING
GAIN AND ADC
TOTAL G = 1000
PATIENT
ISOLATION
BARRIER
DIGITAL DATA
TO SYSTEM
MAINFRAME
A1
A2
A3
Figure 8. Block Diagram, EKG Monitor Front End Using Discrete Components
相关PDF资料 |
PDF描述 |
|---|---|
| AD8225-EVAL | Precision Gain of 5 Instrumentation Amplifier |
| AD8225AR | Precision Gain of 5 Instrumentation Amplifier |
| AD8225AR-REEL7 | Precision Gain of 5 Instrumentation Amplifier |
| AD823AN | Dual, 16 MHz, Rail-to-Rail FET Input Amplifier |
| AD823AR | Dual, 16 MHz, Rail-to-Rail FET Input Amplifier |
相关代理商/技术参数 |
参数描述 |
|---|---|
| AD8225AR | 制造商:Analog Devices 功能描述:SP Amp INSTR Amp Single 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Analog Devices 功能描述:INSTRUMENT AMPLIFIER IC NUMBER OF CIRCUI |
| AD8225AR-REEL | 制造商:Analog Devices 功能描述:SP Amp INSTR Amp Single ±18V/36V 8-Pin SOIC N T/R |
| AD8225AR-REEL7 | 制造商:Analog Devices 功能描述:SP Amp INSTR Amp Single |
| AD8225ARZ | 功能描述:IC AMP INST PREC LP LDRIFT 8SOIC RoHS:是 类别:集成电路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 标准包装:2,500 系列:- 放大器类型:通用 电路数:4 输出类型:- 转换速率:0.6 V/µs 增益带宽积:1MHz -3db带宽:- 电流 - 输入偏压:45nA 电压 - 输入偏移:2000µV 电流 - 电源:1.4mA 电流 - 输出 / 通道:40mA 电压 - 电源，单路/双路(±):3 V ~ 32 V，±1.5 V ~ 16 V 工作温度:0°C ~ 70°C 安装类型:表面贴装 封装/外壳:14-TSSOP（0.173"，4.40mm 宽） 供应商设备封装:14-TSSOP 包装:带卷 (TR) 其它名称:LM324ADTBR2G-NDLM324ADTBR2GOSTR |
| AD8225ARZ-R7 | 功能描述:IC AMP INST PREC LP LDRIFT 8SOIC RoHS:是 类别:集成电路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 标准包装:73 系列:Over-The-Top® 放大器类型:通用 电路数:4 输出类型:满摆幅 转换速率:0.07 V/µs 增益带宽积:200kHz -3db带宽:- 电流 - 输入偏压:1nA 电压 - 输入偏移:285µV 电流 - 电源:50µA 电流 - 输出 / 通道:25mA 电压 - 电源，单路/双路(±):2 V ~ 44 V，±1 V ~ 22 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:16-WFDFN 裸露焊盘 供应商设备封装:16-DFN-EP（5x3） 包装:管件 |
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