Adc Circuit Information; Overview - Analog Devices AD7195 Manual

ADC CIRCUIT INFORMATION

OVERVIEW

The AD7195 is an ultralow noise ADC that incorporates a Σ-Δ
modulator, a buffer, PGA, and on-chip digital filtering intended
for the measurement of wide dynamic range signals, such as
those in pressure transducers, weigh scales, and strain gage
applications. Figure 18 shows the block diagram for the part.
Analog Inputs
The device can be configured to have two differential or four
pseudo differential analog inputs. The analog inputs can be
buffered or unbuffered.
Multiplexer
The on-chip multiplexer increases the channel count of the
device. Because the multiplexer is included on chip, any
channel changes are synchronized with the conversion process.
PGA
The analog input signal can be amplified using the PGA. The
PGA allows gains of 1, 8, 16, 32, 64, and 128.
Reference Detect
The AD7195 is capable of monitoring the external reference. If
the reference is not present, a flag is set in the status register of
the device.
Burnout Currents
Two 500 nA burnout currents are included on-chip to detect
the presence of the external sensor.
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AV DV
AGND
DD
AV
DD
AIN1
AIN2
AIN3
AIN4
MUX
AINCOM
BPDSW
AGND
TEMP
SENSOR
AD7195
ACX1
DGND REFIN(+) REFIN(–)
DD
REFERENCE
INTERFACE
Σ-Δ
PGA
ADC
AC
EXCITATION
CLOCK
ACX1 ACX2 ACX2
Figure 18. Block Diagram
Σ-Δ ADC and Filter
The AD7195 contains a fourth-order Σ-Δ modulator followed
by a digital filter. The device offers the following filter options:
•
4
Sinc
•
3
Sinc
•
Chop enabled/disabled
•
Zero latency
AC Excitation
The AD7195 supports ac excitation of load cells. It provides the
four logic outputs needed to control the transistors in an ac
excited load cell design.
Serial Interface
The AD7195 has a 4-wire SPI. The on-chip registers are
accessed via the serial interface.
Clock
The AD7195 has an internal 4.92 MHz clock. Either this clock
or an external clock can be used as the clock source to the
AD7195. The internal clock can also be made available on a
pin if a clock source is required for external circuitry.
Temperature Sensor
The on-chip temperature sensor monitors the die temperature.
Calibration
Both internal and system calibration are included on chip; thus,
the user has the option of removing offset/gain errors internal
to the AD7195 only, or removing the offset/gain errors of the
complete end system.
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DETECT
DOUT/RDY
SERIAL
DIN
AND
CONTROL
SCLK
LOGIC
CS
SYNC
CLOCK
CIRCUITRY
MCLK1 MCLK2
AD7195