Circuit Note

CN-0371

Circuits from the Lab® reference designs are engineered and

tested for quick and easy system integration tohelp solve today’s

analog, mixed-signal, and RF design challenges. For more

information and/or support, visit www.analog.com/CN0371.

Devices Connected/Referenced

ADA2200

Synchronous Demodulator and

Configurable Analog Filter

AD7192

4.8 kHz, Ultralow Noise, 24-Bit

Sigma-Delta ADC with PGA

ADG794

Low Voltage, 300 MHz, Quad 2:1 Mux

Analog HDTV Audio/Video Switch

ADP151

Ultralow Noise, 200 mA, CMOS

Linear Regulator

Low Power LVDT Signal Conditioner with Synchronous Demodulation

EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Boards

CN-0371 Circuit Evaluation Board (EVAL-CN0371-SDPZ)

System Demonstration Platform (EVAL-SDP-CB1Z)

Design and Integration Files

Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTION AND BENEFITS

The circuit shown in Figure 1 is a complete linear variable

differential transformer (LVDT) signal conditioning circuit that

can accurately measure linear position or linear displacement from

a mechanical reference. Synchronous demodulation in the analog

domain is used to extract the position information and provides

immunity to external noise. A 24-bit, Σ-Δ analog-to-digital

converter (ADC) digitizes the position output for high accuracy.

LVDTs utilize electromagnetic coupling between the movable core

and the coil assembly. This contactless (and hence frictionless)

operation is a primary reason for why they are widely used in

aerospace, process controls, robotics, nuclear, chemical plants,

hydraulics, power turbines, and other applications where

operating environments can be hostile and long life and high

reliability are required.

The entire circuit, including the LVDT excitation signal, consumes

only 10 mW of power. The circuit excitation frequency and output

data rates are SPI programmable. The system has a programmable

bandwidth vs. dynamic range trade-off. It supports bandwidths

of over 1 kHz, and at a bandwidth of 20 Hz, the circuit has a

dynamic range of 100 dB, making it ideal for precision industrial

position and gauging applications.

Figure 1. LVDT Signal Conditioning Circuit (Simplified Schematic: All Connections and Decoupling Not Shown)

0.1µF

0.1µF

0.01µF

0.01µF

0.01µF

100Ω

2.2kΩ

2.2kΩ

100Ω

3.3V

0.1µF

0.1µF

5.0V

3.3V

3.3V

3.3V

5.0V

E-100 SERIES LVDT

4.8kHz

4.92kHz

R33

R4

C4

C24

R34

INP

VOCM

INN

OUTN

OUTP

AIN1

DOUT

DIN

SCLK

CS

AVDD

DVDD

AIN2

MCLK2 AGND DGND

REFIN1(+)

REFIN1(–)

RCLK

GND

CLKIN

VDD

R35

C25

ADG794

ADA2200

AD7192

ADP151

Rev. 0

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