Product category:
Analogue and Mixed Signal ICs
News Release from: Analog Devices | Subject: IDCs and CDCs
Edited by the Electronicstalk Editorial
Team on 08 March 2005
Capacitance and impedance convert to
digital
New high-precision fully integrated convertors address the complex and difficult signal processing challenges of direct capacitance-to-digital and impedance-to-digital conversion.
Analog Devices has developed the world's first high-precision, fully integrated convertors that address the complex and difficult signal processing challenges of direct capacitance-to-digital and impedance-to-digital conversion Combining advanced signal processing techniques with high levels of integration, ADI's capacitance-to-digital convertor (CDC) and impedance-to-digital convertor (IDC) devices attain a level of precision previously only possible with conventional analogue voltage-to-digital convertors aided by a significant number of discrete components
This article was originally published on Electronicstalk on 2 Jul 2008 at 8.00am (UK)
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ADI's devices provide designers significant advantages over existing discrete solutions for capacitance- and impedance-sensing applications that have historically lacked precision and proven difficult and expensive to design.
The devices are ideal for a wide range of high-performance instrumentation and sensing applications, from blood pressure monitors and glucose analysers to position sensors for automobiles and industrial corrosion analysis systems.
ADI's new convertors include the world's first single-chip high-precision capacitance-to-digital convertor (CDC).
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The AD7745 CDC integrates all stages of capacitance-to-digital conversion on one chip reducing costs associated with traditional multichip solutions by 65%.
With 24bit resolution, the AD7745 is the industry's highest-precision solution for interfacing with capacitive sensors.
Ideal for industrial and medical instrumentation and automotive sensing applications.
The AD5933 impedance-to-digital convertor (IDC) combines direct digital synthesis (DDS), analogue-to-digital conversion and digital signal processing techniques to provide a compact, integrated solution for precision impedance measurement, and is ideal for consumer medical, biomedical and industrial instrumentation applications.
"Designers of instrumentation equipment have long recognised the benefits of using capacitive and impedance techniques for applications requiring highly accurate measurements, but up until now they were constrained by complexities in implementation and by the significant design cost involved", said Mike Britchfield, Product Line Director, Precision Convertors, Analog Devices.
"Our advanced CDC and IDC technologies solve these design challenges by delivering the optimal performance levels within an easy-to-use, fully integrated one-chip solution significantly reducing time to market".
Capacitive sensors, which are used to enable high-precision measurements in space-constrained and power-sensitive applications - such as pressure monitoring and position sensing - are extremely robust, accurate and sensitive, but can be costly and difficult to implement.
Traditional capacitance sensor signal processing solutions are either limited to power accuracy applications or require an expensive, multichip capacitance-to-voltage front-end.
ADI's CDCs eliminate these constraints by enabling higher accuracy (24bit resolution) and delivering complete on-chip analogue functionality, while reducing design effort and external component costs.
Because changes in the physical environment can change sensor parameters, the AD7745 is software configurable, eliminating the need for multiple customer product models and expensive hardware reconfiguration, and easing qualification and inventory management.
The software programmable output datarate can be varied from 5 to 90Hz.
At 16.6Hz simultaneous rejection of 50 and 60Hz signals is achieved.
The first three devices in ADI's CDC family - the AD7745, AD7746 and AD7747 - leverage ADI's expertise in high-precision sigma-delta technology and system integration by combining 24bit resolution, low noise of 5aF/(rt)Hz, and low power (1mA maximum) with a complete range of on-chip analogue functions.
These functions include: high-performance, 24bit, sigma-delta analogue-to-digital convertor (ADC); precision low-noise, low-drift voltage reference; temperature sensor; clock; multiplexer; calibration registers; and a two-wire (I2C compatible) serial interface.
This combination of features is well-suited to industrial process control, automotive electronics, and medical applications that demand high precision using the least amount of power and board space.
Impedance measurement is a complex and difficult signal processing challenge, traditionally accomplished using discrete solutions.
The AD5933 and AD5934 combine state-of-the-art digital and analogue signal processing techniques to provide a compact integrated solution for impedance measurement.
Using a direct digital synthesiser (DDS) to provide a fine-frequency sweep capability combined with an analogue-to-digital convertor and sophisticated digital signal processing these devices allow an external complex impedance (range 100ohm to 10Mohm) to be excited with a known frequency of up to approximately 100kHz.
The response signal from the impedance is sampled by the onboard ADC and discrete Fourier transform (DFT) processed by an onboard DSP engine.
The DFT algorithm returns a real and imaginary (I) data word at each frequency point (in the case of a sweep) allowing impedance to be conveniently calculated based on an initial calibration.
All devices are currently sampling with production quantities of the CDCs (AD7745 and AD7746) and the IDCs (AD5933: 12bit, 1Msample/s; and AD5934: 12bit, 250Ksample/s) available in May 2005.
The AD7747 CDC is currently sampling with production quantities available in August 2005.
The devices are available in small 16-lead TSSOPs (thin shrink small outline packages) and 16-lead SSOPs (shrink outline packages) with prices ranging from $4.60 to $4.95 (CDC) and $4.35 to $6.65 (IDC) per unit in 1000-piece quantities.
Higher volume quotes are available on request.
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