AD7846 데이터 시트보기 (PDF) - Analog Devices

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AD7846

LC2MOS 16-Bit Voltage Output DAC

Analog Devices 

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 VREF+ input, the inverting input to the compara-

tor is positive, and if it is in phase with VREF−, the output is nega-

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.

AD7846

ASIN ω t

LVDT x ASIN ω t

–(1–x) ASIN ω t

7 VREF+ VOUT 5

RIN 6

AD7846*

8 VREF–

DGND 20

DB15 DB0

10

3

SIGNAL

GROUND

PROCESSOR DATA BUS

R1

100kΩ

C1

1µF

9

16

10 AD630*

13

*ADDITIONAL PINS OMITTED FOR CLARITY

TO

PROCESSOR PORT

Figure 25. AD7846 in Position Measurement Application

Rev. G | Page 15 of 24

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