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AD698:  Universal LVDT Signal Conditioner

Product Details

The AD698 is a complete, monolithic Linear Variable Differential Transformer (LVDT) signal conditioning subsystem. It is used in conjunction with LVDTs to convert transducer mechanical position to a unipolar or bipolar dc voltage with a high degree of accuracy and repeatability. All circuit functions are included on the chip. With the addition of a few external passive components to set frequency and gain, the AD698 converts the raw LVDT output to a scaled dc signal. The device will operate with half-bridge LVDTs, LVDTs connected in the series opposed configuration (4-wire), and RVDTs.

The AD698 contains a low distortion sine wave oscillator to drive the LVDT primary. Two synchronous demodulation channels of the AD698 are used to detect primary and secondary amplitude. The part divides the output of the secondary by the amplitude of the primary and multiplies by a scale factor. This eliminates scale factor errors due to drift in the amplitude of the primary drive, improving temperature performance and stability.

The AD698 uses a unique ratiometric architecture to eliminate several of the disadvantages associated with traditional approaches to LVDT interfacing. The benefits of this new circuit are: no adjustments are necessary; temperature stability is improved; and transducer interchangeability is improved.


  • Single Chip Solution, Contains Internal Oscillator and Voltage Reference
  • No Adjustments Required
  • Interfaces to Half-Bridge, 4-Wire LVDT
  • DC Output Proportional to Position
  • 20 Hz to 20 kHz Frequency Range
  • Unipolar or Bipolar Output
  • Will Also Decode AC Bridge Signals
  • Outstanding Performance
    Linearity: 0.05%
    Output Voltage: ±11 V
    Gain Drift: 20 ppm/°C (typ)
    Offset Drift: 5 ppm/°C (typ)

Functional Block Diagram for AD698

AD698 Diagram
Functional Block Diagram for AD698


Title Content Type File Type
AD698: Universal LVDT Signal Conditioner Data Sheet (Rev B, 07/1995) (pdf, 230 kB) Data Sheets PDF
CN-0301: Universal LVDT Signal Conditioning Circuit  (pdf, 313 kB) Circuit Note PDF
RAQs index Rarely Asked Questions HTML
Glossary of EE Terms Glossary HTML

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Price, packaging, availability

AD698 Model Options
Model Package Pins Temp.
Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
AD698AP Status: Production 28 ld PLCC 28 Ind Tube, 39 $24.22 $20.99 N  Material Info PCN Purchase
AD698APZ Status: Production 28 ld PLCC 28 Ind Tube, 39 $20.98 $18.17 Y  Material Info Notify Me Purchase
AD698SQ Status: Production 24 ld CerDIP(600 Mil) 24 Mil Tube, 15 $64.22 - N  Material Info PCN Purchase
Price Table Help

The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.

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