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acquisitionZONE Products for the week of June 8, 2009
Microchip Technology Says…
Unveiling Inductive Touch Sensing Analog Front End (AFE)
Fully Integrated AFE Makes it Easier and More Cost Effective to Develop Inductive Touch Sensing User Interfaces
Microchip Technology Inc., a leading provider of microcontroller and analog semiconductors, announced from the Sensors Expo in Chicago the MCP2036 Analog Front End (AFE) for inductive touch-sensing applications. Complimenting the Company’s royalty-free mTouch Inductive Touch-Sensing Solutions, the fully-integrated MCP2036 AFE works with almost any 8-, 16- or 32-bit PIC microcontroller (MCU) or dsPIC Digital Signal Controller (DSC), making it even easier and more cost effective for designers to enhance user interfaces with inductive touch-sensing technology. This inductive-touch AFE includes a multiplexer, a frequency mixer, an amplifier, a driver, and a voltage reference, which drastically lowers component count, and reduces design size and cost. Additionally, the AFE can be easily configured for a variety of applications in the appliance, industrial and automotive markets, among others.
Inductive touch sensing’s fundamental operating principles enable it to work through a front panel, such as plastic, stainless steel or aluminum. The technology also works through thick gloves and on surfaces where liquids are present. These characteristics make inductive touch sensing suitable for applications in the appliance market because of the possibility of a stainless steel front panel; the industrial market because of the technology’s robustness; and the automotive market because of the technology’s sleek aesthetics and ability to reduce accidental-touch triggers.
“Microchip’s inductive-touch technology provides unique capabilities that complement our capacitive touch-sensing products,” said Steve Drehobl, vice president of Microchip’s Security, Microcontroller and Technology Development Division.
Drehobl continued, “With the MCP2036 AFE, we are continuing to make it easier and less expensive for engineers to make use of these unique features for applications requiring metal finishing and robust operation in wet environments.”
EN-Genius Says…
I don’t immediately think of inductive sensing as a practical technology and that is a mistake on my part. There is no reason why that third passive quantity should not be up there with both resistive and capacitive sensing and Microchip proves that to be truly the case.
The technology of inductive touch sensing allows for detection of changes through a variety of materials that would not be possible with other systems: through metals, plastics, thick fabrics (think work gloves), and the rate of change of an inductive touch also means that there will be an identifiable difference between a casual contact and a hard pressure one.
 The MCP2036 is an analog front-end for inductive sensing. It measures the inductive impedance of a sensor coil by exciting it with an on-chip pulse of dc and measuring the amplitude of the generated ac voltage. The drive current is derived from a triangular waveform formed from the PWM output of a microcontroller (the same PWM output also acts as clock for the front-end). The series combination of coils are driven by an external multiplexer/demultiplexer and the derived ac signals are ac coupled from a similar mux/demux. Suggested by Microchip for a 4-key system is the venerable dual 4-channel CD4052BC from Fairchild – a 1983 part with a street price of less than 20 cents in volume, and available in SOIC-16, SOP-16 and PDIP-16. Switching of the mux/demux is also controlled from the microprocessor.
The voltage difference between the sense coils and a reference coil are multiplexed into a synchronous detector (a clock-switched mixer [Switched rectifer, really], amplifier and filter), converting the coil voltages into a pulsed dc signal with a peak level directly proportional to the ac coil voltage. The gain setting resistors and the filter capacitors (in parallel) are external parts. The dc output from the IC will be taken to an ADC input on the microprocessor.
Supply rail for the MCP2036 can be between 2.7 V and 5.5 V with a maximum quiescent, at the higher rail voltage and with a 2 MHz clock, of typically 6.8 mA. The power-down current at that rail is a typical 25 nA.
The output amplifier/filter offers a dc open-loop gain of typically 110 dB with a PSRR of 86 dB and a CMMR of 76 dB. The output voltages are within 20 mV of the rails.
The idea and uses of inductor sensing are extremely attractive in industrial applications where the robustness and unique environment uses offer a substantial improvement over key systems that have to be otherwise protected from fluids and harsh conditions. In medical applications, too, the idea that the sensor can be buried under a fully cleanable surface also makes it attractive. Microchip has an extremely successful product on its hands, one that will sell in huge volumes. However, if it believes that many of the MCP2036 applications will involve the use of a mux/demux such as the CD4052BC it needs to get that functionality on its own IC: designers will grumble about increasing the IC cost by over 50% by having simple analog multiplexing functionality external.
The MCP2036 is in production in QFN-16, PDIP-14 and SOIC-14 with pricing starting at $0.33 in 10-k piece lots.
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