September 1, 1997

Corrections and updates

We provided an incorrect Web address for Arthur D Little in "Web site helps inventors bring creations to market" (EDN, June 19, 1997, pg 20). The correct address is www.adlenterprises.com.

Dither monitors radiation

The "dither" technique that Ken Hatch mentioned in Signals & Noise (EDN, June 5, 1997, pg 45) is similar to a technique used in a radiation-monitoring device (Model 452 alpha continuous air monitor) that SAIC/RaDeCo (San Diego, CA) manufactures. The radiation monitor minimizes the effects of differential nonlinearity in the ADC by spreading repeated measurements of the same input value over several ADC channels. This method smoothes the spectrum and allows better detection but causes a small conversion-range loss.

In the SAIC design, the added error signal is uniformly distributed; Hatch does not specify the distribution of the error signal in his comment. I think this method may be patented, at least in regard to its use in radiation-measuring equipment.

Phil Spray
via the Internet

Simpler is better

I was very interested in "Simplicity pays off in circuit design" (EDN, July 17, 1997, pg 119). At my company, we have a number of applications that require H-bridge drives. Previously, to avoid using expensive P-channel devices, designers employed a high-side driver IC. I replaced that IC with a circuit from the 1920s (updated to use discrete semiconductors). This circuit is now used exclusively across all product lines because it is simpler, cheaper, and because it does not have duty-cycle constraints.

Also, we were using ICs to drive our stepper motors. These ICs were expensive and complicated to implement. They also burned out whenever a firmware crash kept them turned on. When I finally got assigned to a stepper-motor drive, I simply trashed the old design in favor of a discrete power FET bridge, using the trusty high-side booster from the 1920s. Logic was supplied by an FPGA, as it was with the ICs. The beefy 15A FETs never burned out; a device we called a "resistor" provided the current limiting. The resistor lowered the Q of the motor drive, improving transient response.

Dave Wolze
via the Internet

Sound off

Send your letters to Signals and Noise Editor, EDN, 275 Washington St, Newton, MA 02158 or e-mail us at bmorrison@edn.cahners.com. Our fax is 1-617-558-4470. EDN reserves the right to edit letters for clarity and length.

| EDN Access | Feedback | Table of Contents |