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參數(shù)資料
| 型號(hào)： | AB-103 |
| 英文描述： | AB-103 - NOISE ANALYSIS FOR HIGH SPEED OP AMPS |
| 中文描述： | 抗體- 103 -噪聲分析高速運(yùn)算放大器 |
| 文件頁(yè)數(shù)： | 6/6頁(yè) |
| 文件大?。?/td> | 69K |
| 代理商： | AB-103 |
6
This calculation is greatly simplified, but the filter time
constant of 1ms causes the 4.5mV error to settle very slowly,
while the conversion of the selected channel usually should
begin after 100
μ
s or less. For this reason, the error that arises
in the conversion is described as crosstalk. In addition to the
50pF, the external capacitances from the conductors and the
input capacitance of the succeeding amplifier also contribute
to the error. The resulting total error exceeds the LSB
threshold of a 12-bit converter. In the worst scenario, the
preceding channel has –10V while its successor has +10V,
in which case the deviation is already doubled.
These errors can be avoided by either a large C
1
or a low-
pass filter with a very short time constant. As already
mentioned, a short time constant of a few microseconds will
not always be able to produce the desired filter effect. An
amplifier in front of the MUX input decouples the input
filter and drives the multiplexer in low-impedance mode.
This solution eliminates both dynamic overload of the am-
plifier after the MUX and error from the charge transmis-
sion. In addition, the amplifiers can also raise the signal
amplitude and can be configured as active filters.
SUMMARY
Fault currents in the input of the amplifier can be large
enough to generate significant errors. Filters at the input of
a data acquisition multiplexer are practically unavoidable,
yet they can also become a significant source of error. Great
stress is thus placed on the parameters of the sense amplifi-
ers succeeding the multiplexer, especially in high-resolution
systems. The protection circuitry described here with two
FETs is especially recommended for programmable gain
amplifiers (PGAs) since the circuitry of these amplifiers
often produces large overload input currents that can only be
limited externally.
For large signals, amplifiers with FET inputs allow easy
error reduction. Modern FET op amps and INAs now offer
very good DC stability and low voltage noise, making them
preferable to bipolar amplifiers in many applications.
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