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参数资料
| 型号： | AD648J |
| 厂商： | Analog Devices, Inc. |
| 英文描述： | Dual Precision, Low Power BiFET Op Amp |
| 中文描述： | 双路精密低功耗运算放大器BiFET |
| 文件页数： | 10/12页 |
| 文件大小： | 335K |
| 代理商： | AD648J |
AD648
REV. C
–10–
LOG RAT IO AMPLIFIE R
Log ratio amplifiers are useful for a variety of signal condition-
ing applications, such as linearizing exponential transducer out-
puts and compressing analog signals having a wide dynamic
range. T he AD648’s picoamp level input current and low input
offset voltage make it a good choice for the front-end amplifier
of the log ratio circuit shown in Figure 30. T his circuit produces
an output voltage equal to the log base 10 of the ratio of the in-
put currents I
1
and I
2
. Resistive inputs R1 and R2 are provided
for voltage inputs.
Input currents I
1
and I
2
set the collector currents of Q1 and Q2,
a matched pair of logging transistors. Voltages at points A and B
are developed according to the following familiar diode equation:
V
BE
=
(
kT/q
)
ln
(
I
C
/
I
ES
)
In this equation, k is Boltzmann’s constant, T is absolute tem-
perature, q is an electron charge, and I
ES
is the reverse satura-
tion current of the logging transistors. T he difference of these
two voltages is taken by the subtractor section and scaled by a
factor of approximately 16 by resistors R9, R10 and R8. T em-
perature compensation is provided by resistors R8 and R15,
which have a positive 3500 ppm/
°
C temperature coefficient.
T he transfer function for the output voltage is:
V
OUT
=
1
V log
10
(I
2
/I
1
)
Frequency compensation is provided by R11, R12, C1, and C2.
Small signal bandwidth is approximately 300 kHz at input cur-
rents above 100
μ
A and will proportionally decrease with lower
signal levels. D1, D2, R13, and R14 compensate for the effects
of the two logging transistors’ ohmic emitter resistance.
T o trim this circuit, set the two input currents to 10
μ
A and ad-
just V
OUT
to zero by adjusting the potentiometer on A3. T hen
set I
2
to 1
μ
A and adjust the scale factor such that the output
voltage is 1 V by trimming potentiometer R10. Offset adjust-
ment for A1 and A2 is provided to increase the accuracy of the
voltage inputs.
T his circuit ensures a 1% log conformance error over an input
current range of 300 pA to l mA, with low level accuracy limited
by the AD648’s input current. T he low level input voltage accu-
racy of this circuit is limited by the input offset voltage and drift
of the AD648.
Figure 30. Precision Log Ratio Amplifier
相关PDF资料 |
PDF描述 |
|---|---|
| AD648K | Dual Precision, Low Power BiFET Op Amp |
| AD648KN | Dual Precision, Low Power BiFET Op Amp |
| AD648KR | Dual Precision, Low Power BiFET Op Amp |
| AD648S | Dual Precision, Low Power BiFET Op Amp |
| AD648SQ | Dual Precision, Low Power BiFET Op Amp |
相关代理商/技术参数 |
参数描述 |
|---|---|
| AD648JCHIPS | 制造商:AD 制造商全称:Analog Devices 功能描述:Dual Precision, Low Power BiFET Op Amp |
| AD648JN | 制造商:Rochester Electronics LLC 功能描述:LOW POWER DUAL OP AMP IC - Bulk 制造商:Analog Devices 功能描述:IC OP AMP DUAL BIFET DIP8 648 |
| AD648JNZ | 功能描述:IC OPAMP BIFET 1MHZ DUAL LP 8DIP RoHS:是 类别:集成电路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 产品培训模块:Differential Circuit Design Techniques for Communication Applications 标准包装:1 系列:- 放大器类型:RF/IF 差分 电路数:1 输出类型:差分 转换速率:9800 V/µs 增益带宽积:- -3db带宽:2.9GHz 电流 - 输入偏压:3µA 电压 - 输入偏移:- 电流 - 电源:40mA 电流 - 输出 / 通道:- 电压 - 电源，单路/双路(±):3 V ~ 3.6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:16-VQFN 裸露焊盘，CSP 供应商设备封装:16-LFCSP-VQ 包装:剪切带 (CT) 产品目录页面:551 (CN2011-ZH PDF) 其它名称:ADL5561ACPZ-R7CT |
| AD648JNZKL1 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Analog Devices 功能描述: |
| AD648JR | 制造商:Analog Devices 功能描述:OP Amp Dual GP ±18V 8-Pin SOIC N 制造商:Rochester Electronics LLC 功能描述:LOW POWER DUAL OP AMP IC - Bulk 制造商:Analog Devices 功能描述:IC OP-AMP DUAL BIFET |
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