Orchid redesigns precision LCR instrument

Orchid Technologies Engineering and Consulting has recently completed the redesign of its precision LCR instrument.

Chief among the technical improvements and costs reductions were: reduce circuit board count from two to one board; simplify external connection method; simplify complex shielding methods; remove requirement for SRAM battery backup with FRAM; replace floppy drive with USB stick; replace obsolete TMS320C31 DSP with new TMS320C6713 and port firmware accordingly; replace obsolete 32 bit DDS circuitry with new 48 bit DDS circuitry; replace obsolete Burr Brown ADC with SAR converters; reduce most digital logic to a single Altera Cyclone FPGA; and replace through hole components with SMT parts.

Orchid said that the new instrument achieves improved accuracy to 0.01 per cent with a 3x increase in measurement speed.

The original LCR instrument circuit board set required separate analogue 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.

All circuitry (analogue and digital both) is now on a single board, Altera FPGA devices integrate digital functions and system shielding has been simplified.

Orchid said that 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 TMS320C31 DSP from Texas Instruments performed high-speed sine wave correlation functions.

Twenty years ago, these DSP processors used a 32-bit method to represent floating point numbers.

Today, modern DSP processors such as the 200MHz TMS320C6713 can represent floating point numbers with 64-bit precision using industry standard IEEE floating point methods.

Updating the DSP processor required porting the old DSP source code to the new floating point DSP processor.

The benefit was increased mathematical precision together with increased DSP execution speed.

These two factors served to improve instrument precision from 0.05 per cent to 0.01 per cent accuracy.

Taking care to energise digital busses only when required, the design greatly reduces digital signal noise in the precision analogue circuitry.

Modern FPGA technology allows us to replace an entire circuit board with a single high density component.

Back to top