TechBlog

In industrial applications, a digital-to-analog (D-to-A) interface may be rather straightforward but the analog-to-digital (A-to-D) converter (ADC) can be a challenge. The capacitive input stage of both delta-sigma and successive approximation register (SAR) interfaces used for the ADC requires signal capture within a limited time frame. An improper signal chain can cause ringing and oscillation and result in inaccurate readings. However, this is just one of many factors to consider when selecting an ADC.

Signal Chain

High-performance ADCs convert the output of an analog sensor to a digital format for a microcontroller or digital signal processor. The selection of the ADC must be part of a systems approach. “When somebody starts a design, you start with the sensor, you see what kind of output impedance it has and you choose an amplifier and resistors around the amplifier and you choose that configuration based on your sensor,” says Chuck Sins, applications engineer, National Semiconductor. “Based on the accuracy of your sensor and what you are ultimately trying to achieve, then I choose the resolution of the ADC.”

Continue reading ‘Signal Conditioning Issues’ »

The National Institute of Standards and Technology (NIST) has issued its first reference standards for nanoscale particles targeted for the biomedical research community—literally “gold standards” for labs studying the biological effects of nanoparticles. The three new materials, gold spheres nominally 10, 30 and 60 nanometers in diameter, were developed in cooperation with the National Cancer Institute’s Nanotechnology Characterization Laboratory (NCL).

Nanosized particles are the subject of a great deal of biological research, in part because of concerns that in addition to having unique physical properties due to their size, they also may have unique biological properties. On the negative side, nanoparticles may have special toxicity issues. On the positive side, they also are being studied as vehicles for targeted drug delivery that have the potential to revolutionize cancer treatments. Research in the field has suffered from a lack of reliable nanoscale measurement standards, both to ensure consistency of data from one lab to the next and to verify the performance of measurement instruments and analytic techniques.

False color scanning electron micrograph (250,000 times magnification) showing the gold nanoparticles created by NIST and the National Cancer Institute’s Nanotechnology Characterization Laboratory for use as reference standards in biomedical research laboratories.The new NIST reference materials are citrate-stabilized nanosized gold particles in a colloidal suspension in water. They have been extensively analyzed by NIST scientists to assess particle size and size distribution by multiple techniques for dry-deposited, aerosol and liquid-borne forms of the material. Dimensions were measured using six independent methods—including atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential mobility analysis (DMA), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS). At the nanoscale in particular, different measurement techniques can and will produce different types of values for the same particles.

Continue reading ‘NIST Reference Materials Are ‘Gold Standard’ For Bio-Nanotech Research’ »