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參數(shù)資料
| 型號： | LTC1090M |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Single Chip 10-Bit Data Acquisition System |
| 中文描述： | 單芯片10位數(shù)據(jù)采集系統(tǒng) |
| 文件頁數(shù)： | 22/28頁 |
| 文件大小： | 344K |
| 代理商： | LTC1090M |
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22
LTC1090
1090fc
6. Reduced Reference Operation
The effective resolution of the LTC1090 can be increased
by reducing the input span of the converter. The LTC1090
exhibits good linearity and gain over a wide range of
reference voltages (see typical curves of Linearity and
Gain Error vs Reference Voltage). However, care must be
taken when operating at low values of V
REF
because of the
reduced LSB step size and the resulting higher accuracy
requirement placed on the converter. The following factors
must be considered when operating at low V
REF
values:
1. Conversion speed (ACLK frequency)
2. Offset
3. Noise
Conversion Speed with Reduced V
REF
With reduced reference voltages, the LSB step size is
reduced and the LTC1090 internal comparator overdrive is
reduced. With less overdrive, more time is required to
perform a conversion. Therefore, the maximum ACLK
frequency should be reduced when low values of V
REF
are
used. This is shown in the typical curve of Maximum
Conversion Clock Rate vs Reference Voltage.
Offset with Reduced V
REF
The offset of the LTC1090 has a larger effect on the output
code when the A/D is operated with reduced reference
voltage. The offset (which is typically a fixed voltage)
becomes a larger fraction of an LSB as the size of the LSB
is reduced. The typical curve of Unadjusted Offset Error vs
Reference Voltage shows how offset in LSBs is related to
reference voltage for a typical value of V
OS
. For example,
a V
OS
of 0.5mV which is 0.1LSB with a 5V reference
becomes 0.5LSB with a 1V reference and 2.5LSBs with a
0.2V reference. If this offset is unacceptable, it can be
corrected digitally by the receiving system or by offsetting
the “–” input to the LTC1090.
Noise with Reduced V
REF
The total input referred noise of the LTC1090 can be
reduced to approximately 200
μ
V peak-to-peak using a
ground plane, good bypassing, good layout techniques
and minimizing noise on the reference inputs. This noise
is insignificant with a 5V reference but will become a larger
fraction of an LSB as the size of the LSB is reduced. The
typical curve of Noise Error vs Reference Voltage shows
the LSB contribution of this 200
μ
V of noise.
For operation with a 5V reference, the 200
μ
V noise is only
0.04LSB peak-to-peak. In this case, the LTC1090 noise
will contribute virtually no uncertainty to the output code.
However, for reduced references, the noise may become
a significant fraction of an LSB and cause undesirable jitter
in the output code. For example, with a 1V reference, this
same 200
μ
V noise is 0.2LSB peak-to-peak. This will
reduce the range of input voltages over which a stable
output code can be achieved by 0.2LSB. If the reference is
further reduced to 200mV, the 200
μ
V noise becomes
equal to one LSB and a stable code may be difficult to
achieve. In this case averaging readings may be necessary.
This noise data was taken in a very clean setup. Any setup
induced noise (noise or ripple on V
CC
, V
REF
, V
IN
or V
–
) will
add to the internal noise. The lower the reference voltage
to be used, the more critical it becomes to have a clean,
noise-free setup.
Figure 16. Poor Reference Settling Can Cause A/D Errors
HORIZONTAL: 1
μ
s/DIV
V
APPLICATIOU
W
U
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PDF描述 |
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LTC1090MJ | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Single Chip 10-Bit Data Acquisition System |
| LTC1090MJ/883 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Single-Ended Data Acquisition System |
| LTC1091 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:1-, 2-, 6- and 8-Channel, 10-Bit Serial I/O Data Acquisition Systems |
| LTC1091AC | 制造商:LINER 制造商全稱:Linear Technology 功能描述:1-, 2-, 6- and 8-Channel, 10-Bit Serial I/O Data Acquisition Systems |
| LTC1091ACJ8 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Single-Ended Data Acquisition System |
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