2
AD7714
REV. C
–35–
CLOCK
GENERATION
AUTO-ZEROED
MODULATOR
CHARGE BALANCING A/D
CONVERTER
DIGITAL
FILTER
AVDD
1 A
BUFFER
AVDD
SERIAL INTERFACE
REGISTER BANK
STANDBY
SYNC
MCLK IN
MCLK OUT
1 A
REF IN (+)
REF IN (–)
AGND
DGND
BUFFER
DOUT
DIN
CS
SCLK
POL
DRDY
RESET
DVDD
AD7714
DVDD
GND
+5V
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
C
VOUT
AD780
THERMOCOUPLE
JUNCTION
+5V
+VIN
A = 1–128
AGND
R
SWITCHING
MATRIX
PGA
Figure 13. Thermocouple Measurement Using the AD7714
Temperature Measurement
Another application area for the AD7714 is in temperature
measurement. Figure 13 outlines a connection from a thermo-
couple to the AD7714. In this application, the AD7714 is oper-
ated in its buffered mode to allow large decoupling capacitors
on the front end to eliminate any noise pickup which there may
have been in the thermocouple leads. When the AD7714 is
operated in buffered mode, it has a reduced common-mode
range. In order to place the differential voltage from the thermo-
couple on a suitable common-mode voltage, the AIN2 input of
the AD7714 is biased up at the reference voltage, +2.5 V.