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参数资料
| 型号： | AN-242 |
| 厂商： | National Semiconductor Corporation |
| 英文描述： | LJT 18C 18#20 SKT RECP |
| 中文描述： | 应用新的精密运算放大器 |
| 文件页数： | 10/16页 |
| 文件大小： | 267K |
| 代理商： | AN-242 |
Bias current compensation is not used because low-range
accuracy is limited by the leakage currents of Q2 and Q3.
As it is, these parts must be selected for low leakage. This
should not be difficult because the leakage specified is de-
termined by test equipment rather than device characteris-
tics. It should be noted in making substitutions that Q2 was
selected for low pinch-off voltage and that Q3 may have to
dissipate 300 mW on the high-current range. Heating Q3 on
the high range could increase leakage to where the circuit
will not function for a while when switched to the low range.
logarithmic converter
A logarithmic amplifier that can operate over an eight-dec-
ade range is shown in Figure 17. Naturally, bias current
compensation must be used to pick up the low end of this
range. Leakage of the logging transistors is not a problem
as long as Q1A is operated at zero collector-base voltage.
In the worst case, this may require balancing the offset volt-
age of A1. Non-standard frequency compensation is used
on A1 to obtain fairly uniform response time, at least at the
high end of the range. The low end might be improved by
optimizing C1. Otherwise, the circuit is standard.
light meter
This logging circuit is adapted to a battery-powered light
meter in Figure 18. An LM10, combined op amp and refer-
ence, is used for the second amplifier and to provide the
regulated voltage for offsetting the logging circuit and pow-
ering the bias current compensation. Since a meter is the
output indicator, there is no need to optimize frequency
compensation. Low-cost single transistors are used for log-
ging since the temperature range is limited. The meter is
protected from overloads by clamp diodes D2 and D3.
Silicon photodiodes are more sensitive to infrared than visi-
ble light, so an appropriate filter must be used for photogra-
phy. Alternately, gallium-arsenide-phosphide diodes with
suppressed IR response are becoming available.
differential amplifiers
Many instrumentation applications require the measure-
ments of low-level signals in the presence of considerable
ground noise. This can be accomplished with a differential
amplifier because it responds to the voltage between the
inputs and rejects signals between the inputs and ground.
330 ppm/
§
C. Type Q209
available from Tel Labs, Inc.,
Manchester, N.H.
a. set R11 for V
OUT
e
0 at I
IN
e
100 nA
b. set R8 for V
OUT
e
3V at I
IN
e
100
m
A
c. set R3 for V
OUT
e
4V at I
IN
e
10 pA
TL/H/7479–19
Figure 17. Unusual frequency compensation gives this logarithmic converter a 100
m
s time constant from 1 mA down
to 100 nA, increasing from 200
m
s to 200 ms from 10 nA to 10 pA. Optional bias current compensation can
give 10 pA resolution from
b
55
§
C to
a
100
§
C. Scale factor is 1V/decade and temperature compensated.
10
相关PDF资料 |
PDF描述 |
|---|---|
| AN-40 | Application Note 40 |
| AN-5002 | LJT 18C 18#20 SKT WALL RECP |
| AN-5025 | Applications Using the GTLP10B320 |
| AN-5026 | Circular Connector; No. of Contacts:19; Series:MS27656; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:15; Circular Contact Gender:Pin; Circular Shell Style:Wall Mount Receptacle; Insert Arrangement:15-19 RoHS Compliant: No |
| AN-5031 | GTLP Power Configuration |
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