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Texas Instruments inductance to digital converter (LDC): Necessity breeds invention

-September 16, 2013

Texas Instruments designers have developed an entirely new data converter with the LDC1000 inductance-to-digital converter (LDC) designed specifically for inductive sensing applications.

The LDC uniquely combines all of the external circuitry on chip that is normally required to simultaneously measure the impedance and resonant frequency of an LC resonator. It then regulates the oscillation amplitude in a closed loop to a constant level, while it monitors the dissipated energy of the resonator. This leads the accurate measurement of inductance of the front-end LC circuit, which enables precise measurement of linear/angular position, displacement, motion, compression, vibration, metal composition and new applications which will be conceived by designers. All of this can be done in the presence of oil, dust, dirt and moisture unlike most other solutions.

What this means to designers is that the applications, beyond the obvious ones mentioned below, are still to be developed as creative minds will find uses for this device in areas that might not be evident right now.

Yes, necessity breeds invention, so new design needs will find that this unique device can be used in ways in which  no other device is capable. Existing sensor technologies shortfalls can be eliminated with the front-end capabilities, compactness, low cost, low power and sheer flexibility of this LDC.  It may well have you rethink your use of currently popular Hall-effect, pressure, ohmic, capacitive, optical and ultrasonic sensors.

I have been in the electronics industry for 41 years. I remember back in the 70s when analog-to-digital converters (ADCs) were on PC cards - the sample-and-hold amplifier, reference and the A/D converter all constructed in hybrid form on ceramic substrates. The 80s brought about ADCs in big rectangular metal cans, still with a hybrid technology on a ceramic substrate. Then came the 90s with monolithic die ADCs with and without sample-and-hold amplifier in ceramic and then plastic packages.

As time went on, ADCs attained better performance in accuracy, dynamic range, speed and other areas. Then came the delta sigma ADC in which we could overcome the Brownian motion noise floor that was a part of physics that seemingly limited dynamic range. That is, until designers got the clever idea of pushing the noise up in frequency out of the band of interest - the delta sigma ADC was born.

Many variations and higher integration designs like analog front ends (AFEs) were done with ADCs, but really no great new innovation had come about in recent years. Until today.

An entirely new data converter category that I think is exciting and innovative is on the scene as of today with the industry’s first inductance-to-digital converter, the Texas Instruments LDC1000.

Inductive sensing
Inductive sensors can detect metal objects without touching them. They are sometimes used as a proximity detector or position sensor in factory automation and other areas. The operating principle is the use of a coil and an oscillator to create a magnetic field surrounding the sensing surface. The metallic object or “actuator” causes a dampening of the amplitude of the oscillation which can be used and detected in various ways to manage, position and control a process.

Figure 1: The LDC, brings to position and motion sensing, better performance, reliability and flexibility while lowering system cost and power

Applications
The new device is only limited by the designer’s imagination and creativity. There are a myriad of uses in industrial, automotive, consumer, medical, computing & mobile devices and communications, just to name a few.

There is a great need in the market today for sensing devices to operate in harsh environments and be immune to contaminants. Green solutions are expected, no demanded, by the market. Sensors are expected to reduce costs and R&D and new sensing capabilities are needed.

Existing sensing technologies
Some of the top sensing technologies on the market today and their applications can be found right here. All sensors have their strengths and weaknesses. The following Figure 2 shows some drawbacks in existing sensor technologies.

Figure 2: Various sensors and their challenges


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