參數(shù)資料
型號: AD7147WPACPZ-500R7
廠商: Analog Devices Inc
文件頁數(shù): 18/73頁
文件大小: 0K
描述: IC CAP-TO-DGTL CONV PROG 24LFCSP
標準包裝: 500
系列: CapTouch™
類型: 電容數(shù)字轉換器
分辨率(位): 16 b
采樣率(每秒): 250k
數(shù)據(jù)接口: 串行,SPI?
電壓電源: 單電源
電源電壓: 2.6 V ~ 3.6 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 24-VFQFN 裸露焊盤,CSP
供應商設備封裝: 24-LFCSP-VQ(4x4)
包裝: 帶卷 (TR)
AD7147
Data Sheet
Rev. D | Page 24 of 72
ENVIRONMENTAL CALIBRATION
CD
C
O
U
T
P
UT
CO
DE
S
t
STAGEx_LOW_THRESHOLD
STAGEx_HIGH_THRESHOLD
CDC AMBIENT VALUE
CHANGING ENVIRONMENTAL CONDITIONS
SENSOR 1 INT
ASSERTED
SENSOR 2 INT
ASSERTED
06
66
3-
03
2
The AD7147 provides on-chip capacitance sensor calibration to
automatically adjust for environmental conditions that have an
effect on the ambient levels of the capacitance sensor. The output
levels of the capacitance sensor are sensitive to temperature,
humidity, and, in some cases, dirt.
The AD7147 achieves optimal and reliable sensor performance
by continuously monitoring the CDC ambient levels and compen-
sating for any environmental changes by adjusting the values of
the STAGEx_HIGH_THRESHOLD register and the STAGEx_
LOW_THRESHOLD registers as described in the Threshold
Equations section. The CDC ambient level is defined as the
output level of the capacitance sensor during periods when the
user is not approaching or in contact with the sensor.
Figure 35. Ideal Sensor Behavior with a Constant Ambient Level
CAPACITANCE SENSOR BEHAVIOR WITHOUT
CALIBRATION
After the AD7147 is configured, the compensation logic runs
automatically with each conversion when the AD7147 is not
being touched. This allows the AD7147 to compensate for
rapidly changing environmental conditions.
Figure 36 shows the typical behavior of a capacitance sensor
when calibration is not applied. This figure shows ambient
levels drifting over time as environmental conditions change. As
a result of the initial threshold levels remaining constant while
the ambient levels drift upward, Sensor 2 fails to detect a user
contact in this example.
The ambient compensation control registers provide the host
with access to general setup and controls for the compensation
algorithm. On-chip RAM stores the compensation data for each
conversion stage, as well as setup information specific for each stage.
describes how the AD7147 adaptive calibration algorithm
prevents such errors from occurring.
Figure 35 shows an example of the ideal behavior of a capaci-
tance sensor, where the CDC ambient level remains constant
regardless of the environmental conditions. The CDC output
shown is for a pair of differential button sensors, where one
sensor caused an increase and the other caused a decrease in
measured capacitance when activated. The positive and negative
sensor threshold levels are calculated as a percentage of the
STAGEx_OFFSET_HIGH and STAGEx_OFFSET_LOW values
and are based on the threshold sensitivity settings and the
ambient value. These values are sufficient to detect a sensor
contact and result in the AD7147 asserting the INT output
when the threshold levels are exceeded.
CDC
O
UT
P
UT
CO
DE
S
t
CDC AMBIENT
VALUE DRIFTING
CHANGING ENVIRONMENTAL CONDITIONS
STAGEx_HIGH_THRESHOLD
STAGEx_LOW_THRESHOLD
SENSOR 1 INT
ASSERTED
SENSOR 2 INT
NOT ASSERTED
0666
3-
033
Figure 36. Typical Sensor Behavior Without Calibration
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