AD7148 Analog Devices, AD7148 Datasheet - Page 27

• Manufacturer Part Number: AD7148
• Manufacturer: Analog Devices

Specifications of AD7148

• Resolution (bits): 16bit
• # Chan: 8
• Sample Rate: 250kSPS
• Interface: I²C/Ser 2-Wire,Ser
• Analog Input Type: SE-Uni
• Ain Range: ± 8 pF (Delta C)
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

AC
The AD7148 measures capacitance between CINx and ground.
Any capacitance to ground on the signal path between the CINx
pins and the sensor is included in the conversion result.
To eliminate the stray capacitance to ground, the AC
should be used to shield the connection between the sensor and
CINx, as shown in Figure 37. The plane around the sensors
should also be connected to AC
SHIELD
OUTPUT
SHIELD
.
SHIELD
signal
Rev. A | Page 27 of 56
Figure 37. AC
SHIELD
The AC
tion signal on CINx. Therefore, there is no ac current between
CINx and AC
does not affect the CINx charge transfer.
Using AC
means that the AD7148 can be placed up to 60 cm away from
the sensors. This allows the AD7148 to be placed on a separate
PCB from the sensors, provided that the connections between
the sensors and the CINx inputs are correctly shielded, using
AC
SHIELD
SHIELD
.
CIN0
CIN1
CIN2
CIN3
SHIELD
output is the same signal waveform as the excita-
SHIELD
AC
AD7148
eliminates capacitance-to-ground pick-up, which
SHIELD
, and any capacitance between these pins
AD7148