AD7846 Analog Devices, AD7846 Datasheet - Page 15

• Manufacturer Part Number: AD7846
• Description: 16-Bit Voltage Output CMOS DAC
• Manufacturer: Analog Devices

Specifications of AD7846

• Resolution (bits): 16bit
• Dac Update Rate: 143kSPS
• Dac Settling Time: 7µs
• Max Pos Supply (v): +15.75V
• Single-supply: No
• Dac Type: Voltage Out
• Dac Input Format: Par

POSITION MEASUREMENT APPLICATION
Figure 25 shows the AD7846 in a position measurement applica-
tion using an linear variable displacement transducer (LVDT),
an AD630 synchronous demodulator and a comparator to make
a 16-bit LVDT-to-digital converter. The LVDT is excited with a
fixed frequency and fixed amplitude sine wave (usually 2.5 kHz,
2 V p-p). The outputs of the secondary coil are in antiphase and
their relative amplitudes depend on the position of the core in the
LVDT. The AD7846 output interpolates between these two inputs
in response to the DAC input code. The AD630 is set up so that
it rectifies the DAC output signal. Thus, if the output of the DAC is
in phase with the V
tor is positive, and if it is in phase with V
tive. By turning on each bit of the DAC in succession starting
with the MSB and deciding to leave it on or turn it off based on
the comparator output, a 16-bit measurement of the core position
is obtained.
REF+
input, the inverting input to the compara-
REF−
, the output is nega-
Rev. G | Page 15 of 24
*ADDITIONAL PINS OMITTED FOR CLARITY
ASIN ω t
Figure 25. AD7846 in Position Measurement Application
LVDT
–(1–x) ASIN ω t
x ASIN ω t
100kΩ
C1
1µF
R1
7
8
10
13
9
DB15
V
V
AD7846*
10
REF+
REF–
AD630*
PROCESSOR DATA BUS
DGND
V
TO
PROCESSOR PORT
DB0
OUT
R
3
16
IN
20
5
6
SIGNAL
GROUND
AD7846