Position Sensing

The circuit shown in Figure 1 is a complete high performance resolver-to-digital (RDC) circuit that accurately measures angular position and velocity in automotive, avionics, and critical industrial applications where high reliability is required over a wide temperature range.

The circuit has an innovative resolver rotor driver circuit that has two modes of operation: high performance and low power. In the high performance state, the system operates on a single 12 V supply and can supply 6.4 V rms (18 V p-p) to the resolver. In the low power state, the system operates on a single 6 V supply and can supply 3.2 V rms (9.2 V p-p) to the resolver, with less than 100 mA of current consumption. Active filtering is provided in both the driver and receiver to minimize the effects of quantization noise.

The maximum tracking rate of the RDC is 3125 rps in the 10-bit mode (resolution = 21 arc min) and 156.25 rps in the 16-bit mode (resolution = 19.8 arc sec).

The circuit shown in Figure 1 is a high performance, resolver-to-digital converter (RDC) circuit that accurately measures angular position and velocity in automotive, avionics, and critical industrial applications where high reliability is required over a wide temperature range. The AD8397 high current driver can supply 310 mA into a 32 Ω load and eliminates the requirement for discrete push-pull buffer solutions.

Common applications of RDCs are in automotive and industrial markets to provide motor shaft position and/or velocity feedback. 

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.

The circuit shown in Figure 1 is a complete adjustment-free linear variable differential transformer (LVDT) signal conditioning circuit. This circuit can accurately measure linear displacement (position).

The LVDT is a highly reliable sensor because the magnetic core can move without friction and does not touch the inside of the tube. Therefore, LVDTs are suitable for flight control feedback systems, position feedback in servomechanisms, automated measurement in machine tools, and many other industrial and scientific electromechanical applications where long term reliability is important.

This circuit uses the AD598 LVDT signal conditioner that contains a sine wave oscillator and a power amplifier to generate the excitation signals that drive the primary side of the LVDT. The AD598 also converts the secondary output into a dc voltage. The AD8615 rail-to-rail amplifier buffers the output of the AD598 and drives a low power 12-bit successive approximation analog-to-digital converter (ADC). The system has a dynamic range of 82 dB and a system bandwidth of 250 Hz, making it ideal for precision industrial position and gauging applications.

The signal conditioning circuitry of the system consumes only 15 mA of current from the ±15 V supply and 3 mA from the +5 V supply, making this ideal for remote applications. The circuit can operate a remote LVDT from up to 300 feet away, and the output can drive up to 1000 feet.

This circuit note discusses basic LVDT theory of operation and the design steps used to optimize the circuit shown in Figure 1 for a chosen bandwidth, including noise analysis and component selection considerations.

The compact two-chip circuit shown in Figure 1 provides a contactless anisotropic magnetoresistive (AMR) measurement solution ideal for either angle or linear position measurements. The two-chip system is capable of providing better than 0.2° angular accuracy over 180°, and linear accuracy of 2 mil (0.002 inch) over a 0.5 inch range, depending on the size of the magnet used.

The circuit is ideal for applications where high speed, accurate, noncontact angle and length measurements are critical, such as machine tool speed control, crane angle control, brushless dc motors, and other industrial or automotive applications.

The AD2S1210 is a complete 10-bit to 16-bit resolution tracking resolver-to-digital converter, integrating an on-board programmable sinusoidal oscillator that provides sine wave excitation for resolvers.

The converter accepts 3.15 V p-p ± 27% input signals, in the range of 2 kHz to 20 kHz on the sine and cosine inputs. A Type II servo loop is employed to track the inputs and convert the input sine and cosine information into a digital representation of the input angle and velocity. The maximum tracking rate is 3125 rps.

The AD2S1210WDSTZ and the AD2S1210WDSTZRL7 models have been approved by an independent accredited body for use in Automotive Safety Integrity Level B rated applications according to ISO 26262. Contact your local Analog Devices, Inc., sales office to obtain a copy of the safety manual and ASIL B safety assessment certificate.

PRODUCT HIGHLIGHTS

1. Ratiometric tracking conversion. The Type II tracking loop provides continuous output position data without conversion delay. It also provides noise immunity and tolerance of harmonic distortion on the reference and input signals.
2. System fault detection. A fault detection circuit can sense loss of resolver signals, out-of-range input signals, input signal mismatch, or loss of position tracking. The fault detection threshold levels can be individually programmed by the user for optimization within a particular application.
3. Input signal range. The sine and cosine inputs can accept differential input voltages of 3.15 V p-p ± 27%.
4. Programmable excitation frequency. Excitation frequency is easily programmable to a number of standard frequencies between 2 kHz and 20 kHz.
5. Triple format position data. Absolute 10-bit to 16-bit angular position data is accessed via either a 16-bit parallel port or a 4-wire serial interface. Incremental encoder emulation is in standard A-quad-B format with direction output available.
6. Digital velocity output. 10-bit to 16-bit signed digital velocity accessed via either a 16-bit parallel port or a 4-wire serial interface.

APPLICATIONS

• DC and ac servo motor control
• Encoder emulation
• Electric power steering
• Electric vehicles
• Integrated starter generators/alternators
• Automotive motion sensing and control

The AD7357 is a dual, 14-bit, high speed, low power, successive approximation ADC that operates from a single 2.5 V power supply and features throughput rates of up to 4.2 MSPS. The part contains two ADCs, each preceded by a low noise, wide bandwidth track-and-hold circuit that can handle input frequencies in excess of 110 MHz.

The conversion process and data acquisition use standard control inputs allowing for easy interfacing to microprocessors or DSPs. The input signal is sampled on the falling edge of CS; conversion is also initiated at this point. The conversion time is determined by the SCLK frequency.

The AD7357 uses advanced design techniques to achieve very low power dissipation at high throughput rates. With a 2.5 V supply and a 4.2 MSPS throughput rate, the device consumes 14 mA typically. The part also offers flexible power/throughput rate management when operating in normal mode as the quiescent current consumption is so low.

The analog input range for the device is the differential common mode ±V_REF/2. The AD7357 has an on-chip 2.048 V reference that can be overdriven when an external reference is preferred.

The AD7357 is available in a 16-lead thin shrink small outline package (TSSOP) and an 18-lead lead frame chip scale package (LFCSP).

PRODUCT HIGHLIGHTS

1. Two Complete ADC Functions.
   These functions allow simultaneous sampling and conversion of two channels. The conversion result of both channels is simultaneously available on separate data lines or in succession on one data line if only one serial port is available.
2. High Throughput with Low Power Consumption. 
   The AD7357 offers a 4.2 MSPS throughput rate with 36 mW power consumption.
3. Simultaneous Sampling.
   The part features two standard successive approximation ADCs with accurate control of the sampling instant via a CS input and once off conversion control.

APPLICATIONS

• Automotive radar
• Data acquisition systems
• Motion control
• I and Q demodulation
• RFID readers

The ADA4500-2 is a dual 10 MHz, 14.5 nV/√Hz, low power amplifier featuring rail-to-rail input and output swings while operating from a 2.7 V to 5.5 V single power supply. Compatible with industry-standard nominal voltages of +3.0 V, +3.3 V, +5.0 V, and ±2.5 V.

Employing a novel zero-crossover distortion circuit topology, this amplifier offers high linearity over the full, rail-to-rail input common-mode range, with excellent power supply rejection ratio (PSRR) and common-mode rejection ratio (CMRR) performance without the crossover distortion seen with the traditional complementary rail-to-rail input stage. The resulting op amp also has excellent precision, wide bandwidth, and very low bias current.

This combination of features makes the ADA4500-2 an ideal choice for precision sensor applications because it minimizes errors due to power supply variation and maintains high CMRR over the full input voltage range. The ADA4500-2 is also an excellent amplifier for driving analog-to-digital converters (ADCs) because the output does not distort with the common-mode voltage, which enables the ADC to use its full input voltage range, maximizing the dynamic range of the conversion subsystem.

Many applications such as sensors, handheld instrumentation, precision signal conditioning, and patient monitors can benefit from the features of the ADA4500-2.

The ADA4500-2 is specified for the extended industrial temperature range (−40°C to +125°C) and available in the standard 8-lead MSOP and 8-lead LFCSP packages.

Applications

• Pressure and position sensors
• Remote security 
• Medical monitors
• Process controls 
• Hazard detectors
• Photodiode applications

The AD598 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 AD598 converts the raw LVDT secondary output to a scaled dc signal. The device can also be used with RVDT transducers.

The AD598 contains a low distortion sine wave oscillator to drive the LVDT primary. The LVDT secondary output consists of two sine waves that drive the AD598 directly. The AD598 operates upon the two signals, dividing their difference by their sum, producing a scaled unipolar or bipolar dc output.

The AD598 uses a unique ratiometric architecture (patent pending) to eliminate several of the disadvantages associated with traditional approaches to LVDT interfacing. The benefits of this new circuit are: no adjustments are necessary, transformer null voltage and primary to secondary phase shift does not affect system accuracy, temperature stability is improved, and transducer interchangeability is improved.

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.

The AD698 is available in two performance grades:

The ADA4571-2 is a 2-channel anisotropic magneto resistive (AMR) sensor with integrated signal conditioning amplifiers and ADC drivers. The device produces analog outputs that indicate the angular position of the surrounding magnetic field.

Each channel consists of two die within one package: an AMR sensor and a variable gain instrumentation amplifier. The ADA4571-2 delivers clean and amplified cosine and sine output signals per channel related to the angle of a rotating magnetic field. The output voltage range is ratiometric to the supply voltage.

Each sensing channel contains two separated wheatstone bridges at a relative angle of 45° to one another. A rotating magnetic field parallel to the plane of the IC package delivers two sinusoidal output signals, with the double frequency of the angle, α, between the sensor and the magnetic field direction. Within a homogeneous field parallel to the plane of the IC package, the output signals are independent of airgap between the sensor and the magnet.

The ADA4571-2 is available in a 16-lead SOIC package.

Product Highlights

1. Contactless angular measurement.
2. Measures magnetic field direction rather than field intensity.
3. Minimum sensitivity to air gap variations.
4. Large working distance.
5. Excellent accuracy, even for weak saturation fields.
6. Minimal thermal and lifetime drift.
7. Negligible hysteresis.
8. Single-chip solution.

Applications

• Permanent magnet synchronous motor (PMSM) control and positioning
• Contactless angular measurement and detection 
• Magnetic angular position sensing

The AD7380/AD7381 are a 16-bit and 14-bit pin-compatible family of dual simultaneous sampling, high speed, low power, successive approximation register (SAR) analog-to-digital converters (ADCs) that operate from a 3.0 V to 3.6 V power supply and feature throughput rates up to 4 MSPS. The analog input type is differential, accepts a wide common-mode input voltage, and is sampled and converted on the falling edge of CS.

An integrated on-chip oversampling block improves dynamic range and reduces noise at lower bandwidths. A buffered internal 2.5 V reference is included. Alternatively, an external reference up to 3.3 V can be used.

The conversion process and data acquisition use standard control inputs allowing simple interfacing to microprocessors or digital signal processors (DSPs). The device is compatible with 1.8 V, 2.5 V, and 3.3 V interfaces using the separate logic supply.

The AD7380/AD7381 are available in a 16-lead lead frame chip scale package (LFCSP) with operation specified from −40°C to +125°C.

Product highlights

1. Dual simultaneous sampling and conversion with two complete ADC functions.
2. Pin-compatible product family.
3. High 4 MSPS throughput rate.
4. Space saving 3 mm × 3 mm LFCSP.
5. An integrated oversampling block to increase dynamic range, reduce noise, and reduce SCLK speed requirements.
6. Differential analog inputs with wide common-mode range.
7. Small sampling capacitor reduces amplifier drive burden.

Applications

• Motor control position feedback
• Motor control current sense
• Sonar
• Power quality
• Data acquisition systems
• Erbium doped fiber amplifier (EDFA) applications
• I and Q demodulation

The AD7380/AD7381 are a 16-bit and 14-bit pin-compatible family of dual simultaneous sampling, high speed, low power, successive approximation register (SAR) analog-to-digital converters (ADCs) that operate from a 3.0 V to 3.6 V power supply and feature throughput rates up to 4 MSPS. The analog input type is differential, accepts a wide common-mode input voltage, and is sampled and converted on the falling edge of CS.

An integrated on-chip oversampling block improves dynamic range and reduces noise at lower bandwidths. A buffered internal 2.5 V reference is included. Alternatively, an external reference up to 3.3 V can be used.

The conversion process and data acquisition use standard control inputs allowing simple interfacing to microprocessors or digital signal processors (DSPs). The device is compatible with 1.8 V, 2.5 V, and 3.3 V interfaces using the separate logic supply.

The AD7380/AD7381 are available in a 16-lead lead frame chip scale package (LFCSP) with operation specified from −40°C to +125°C.

Product highlights

1. Dual simultaneous sampling and conversion with two complete ADC functions.
2. Pin-compatible product family.
3. High 4 MSPS throughput rate.
4. Space saving 3 mm × 3 mm LFCSP.
5. An integrated oversampling block to increase dynamic range, reduce noise, and reduce SCLK speed requirements.
6. Differential analog inputs with wide common-mode range.
7. Small sampling capacitor reduces amplifier drive burden.

Applications

• Motor control position feedback
• Motor control current sense
• Sonar
• Power quality
• Data acquisition systems
• Erbium doped fiber amplifier (EDFA) applications
• I and Q demodulation