Adc Circuit Information; Overview - Analog Devices AD7194 Manual

ADC CIRCUIT INFORMATION

OVERVIEW

The AD7194 is an ultralow noise ADC that incorporates a
sigma-delta (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 21 shows the basic connections
required to operate the part.
Analog Inputs
The device can be configured to have four differential or eight
pseudo differential analog inputs. The analog inputs can be
buffered or unbuffered. The AD7194 uses flexible multiplexing,
thus any analog input pin can be selected as a positive input
and any analog input pin can be selected as a negative input.
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 AD7194 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 AGND
DD
AIN1/P3
AIN2/P2
AIN3/P1/REFIN2(+)
AIN4/P0/REFIN2(–)
AIN5
MUX
AIN16
AINCOM
AGND
TEMP
SENSOR
Figure 21. Basic Connection Diagram
DV DGND REFIN1(+) REFIN1(–)
DD
AD7194
V
DD
Σ-Δ
PGA
ADC
Σ-Δ ADC and Filter
The AD7194 contains a fourth-order Σ-Δ modulator followed
by a digital filter.
The device has several filter options:
•
4
Sinc
•
3
Sinc
•
Chop enabled/disabled
•
Fast settling
•
Zero latency
Serial Interface
The AD7194 has a 4-wire SPI. The on-chip registers are
accessed via the serial interface.
Clock
The AD7194 has an internal 4.92 MHz clock. Either this clock
or an external clock can be used as the clock source to the AD7194.
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.
Digital Outputs
The AD7194 has four general-purpose digital outputs. These
can be used for driving external circuitry. For example, an
external multiplexer can be controlled by these outputs.
Calibration
Both internal and system calibration are included on chip;
therefore, the user has the option of removing offset/gain errors
internal to the AD7194 only, or removing the offset/gain errors
of the complete end system.
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REFERENCE
DETECT
DOUT/RDY
SERIAL
INTERFACE
DIN
AND
CONTROL
SCLK
LOGIC
CS
CLOCK
CIRCUITRY
MCLK1 MCLK2
AD7194