Oct 07, 2008
"Our first step was to study the existing design," says Paul Nickelsberg, President and Senior Engineer with Orchid Technologies. "We worked to put ourselves into the minds of the original designers." "Through a process of study and review we identified a redesign approach." "We generated a detailed development plan proposing significant technical improvements and cost reductions." "Then we set to work."
Chief among the technical improvements and costs reductions were i) reduce circuit board count from two to one board, ii) simplify external connection method, iii) simplify complex shielding methods, iv) remove requirement for SRAM battery backup with FRAM, v) replace floppy drive with USB stick, vi) replace obsolete TMS320C31 DSP with new TMS320C6713 and port firmware accordingly, vii) replace obsolete Analog Devices 32 bit DDS circuitry with new 48 bit DDS circuitry improving sine wave spectral purity thereby, viii) replace obsolete Burr Brown (TI) Analog to Digital Converters with new Analog Devices SAR converters, ix) reduce most digital logic to a single Altera Cyclone FPGA, x) replace through hole components with SMT parts. Our new instrument is form, fit, and function compatible with the old, while achieving improved accuracy to 0.01% with a 3x increase in measurement speed.
The original LCR instrument circuit board set required separate analog and digital circuit boards to perform its functions. These circuit boards were shielded with a complex jumble of sheet metal, spacers, and screws. Additionally, expensive coax cables were installed to make the DUT connection. Orchid's new design is elegantly simple. All circuitry (analog and digital both) is now on a single board, Altera FPGA devices integrate digital functions and system shielding has been simplified. The result is a lower cost, easier to build easier to service assembly that has another five to seven years product life.
An obsolete 33MHz Texas Instruments TMS320C31 DSP performed high speed sine wave correlation functions. Twenty years ago, TI's DSP processors used a TI-proprietary 32 bit method to represent floating point numbers. Today modern TI DSP processors such as the 200MHz TMS320C6713 can represent floating point number with 64 bit precision using industry standard IEEE floating point methods. Updating the DSP processor required that we port the old DSP source code to the new floating point DSP processor. The benefit was greatly increased mathematical precision together with vastly increased DSP execution speed. These two factors alone served to improve instrument precision from 0.05% to 0.01% accuracy.
Integration of digital circuitry onto a single Altera FPGA both saves space and reduces overall digital system signal noise. Taking care to energize digital busses only when required, the new design greatly reduces digital signal noise in the precision analog circuitry. Modern FPGA technology allows us to replace an entire circuit board with a single high density component.
"Re-design of this precision LCR instrument was one of the more challenging re-design efforts we at Orchid Technologies have undertaken," explained Nickelsberg. "It required a multidisciplinary approach involving mechanical packaging, shielding, precision analog design, integrated digital design, firmware and software development talent." "Our ability to put all those pieces into play has resulting in the successful redesign of this product giving our client another profitable decade of production."
For more information on redesign, contact Paul Nickelsberg, President and Senior Engineer with Orchid Technologies Engineering & Consulting at 978-461-2000 X111 or email at info@orchid-tech.com.
