San Francisco Cypress Semiconductor Corp. will announce this week an extension to its PSoC technology that will optimize the programmable system-on-chip device for capacitive sensing and control applications. Called CapSense, the firmware module equips Cypress' CY8C21x34 PSoC to perform capacitive measurements.
Touch-sensitive capacitive sensors are increasingly used in cell phones, laptops, digital still cameras, white goods and industrial controls, said George Saul, president of the Cypress Microsystems subsidiary that produces the PSoC. "The 'click wheel' control on the Apple iPod is what made capacitive sensing fashionable," Saul said.
A capacitive slider replaces the mechanical scroll wheels, touchpads or potentiometers used for variable control. In new-generation cell phones, the market potential can be as high as 560 million units, Saul believes, or 80 percent of the 700 million phones shipped annually.
The PSoC is essentially an 8-bit microcontroller with built-in analog front and back ends. The CY8C21x34 comes with 8 kbytes of flash for program storage and 512 bytes of SRAM for data, and clocks at 24 MHz. Its configurable analog blocks include A/D and D/A converters, programmable-gain amplifiers and comparators. With its graphical programming tools, the PSoC can implement filters, timers, pulse-width modulators and a variety of parallel and serial interface controllers.
With CapSense, the PSoC serves as a relaxation oscillator, putting a programmable current to the capacitive element. The frequency of the oscillator is altered where the pressure of a finger changes the thickness of the capacitor's dielectric (typically, 3 to 4 mm of ABS plastic). The oscillator works over a 60- to 200-kHz range, said Matt Basinger, product-marketing engineer. The sensitivity of the PSoC component is to within 10 cycles. Thus, the CapSense component can capture variations in frequency from 20 percent to as small as 0.1 percent.
By integrating functions on-chip, the PSoC can reduce the board size and bills of materials ordinarily required to implement capacitive sensing, Cypress said. Traditional control applications often use one sensor signal conditioner for every button on the front panel. The use of a PSoC on a hotel door's electronic key lock slashed the component count from 90 to 28, while an industrial battery charger went from more than 70 components to 23 with PSoC, said Basinger.
The CY8C21x34 PSoC starts at 99 cents in production quantities. A front-panel display demonstration kit (CY3220-FPD) is available for $75 through www.cypress.com/CapSense.