Delta-Sigma oversampled A/D converter principle

Delta-sigma oversampled systems, particularly A/D converters are very useful circuits. This is specially true now when the semiconductor line widths are decreasing significantly and purely analog converters are becoming hard to design and implement in VLSI technology. A delta - sigma converter is mostly digital with a small amount of analog circuitry. As fine line technology is well suited to digital implementation a delta - sigma converter can be very useful indeed. A brief paper on the delta-signal principle was released by Signal Processing Group Inc. and may be found under the free reports accessed by registering on the SPG website by interested readers. Please visit http://www.signalpro.biz.

MEMS cantilever beam and electrostic actuation

One of the very basic MEMS structures is the cantilever beam. This structure can be used in a variety of applications including RF switching, varactors, switches, capacitors, springs etc. Among the many ways to actuate the operation of a cantilever is electrostatics. In this case a voltage is applied across the movable arm of the beam and a baseplate or reference terminal that resides directly below the beam. To bend the beam and to make contact with the baseplate a pull in voltage is necessary. Once the applied voltage reaches the pull in voltage the beam bends and makes contact with the base plate. When the pull in voltage is removed the spring force of the beam restores it to its original state, as long the elastic limits of the beam are not exceeded. A brief whitepaper on this operation is available to interested parties in the engineering pages of Signal Processing Group Inc's website located at http://www.signalpro.biz.

A simple planar inductor

In Integrated Circuit design and MMIC design, integrated planar inductors are used frequently. These inductors have typically lower quality factors. However, in a variety of applications planar inductors can be used effectively. The simplest planar inductor is a length of high characteristic impedance microstrip line. A brief paper published by Signal Processing Group Inc.,provides design equations for this type of structure. Interested readers can view the paper at SPG's website, http://www.signalpro.biz on the engineering pages web page.

MEMS design tools

Its interesting how the MEMS design development is paralleling the IC design methodology of yesteryear. The process appears to be very similar,only the parameters seem to change. We also see UC Berkeley developing methodology and CAD tools. MIT is also an early entrant into the CAD Tool fray. Commercially available tools from Coventor are available ( for a significant cost) but may be the best deal for the design engineer interested in end results rather than the process. It remains to be seen how this whole industry pans out. However, already there are large numbers of MEMS devices working in commercial systems so the MEMS approach is beginning to make sense. Contact SPG at http://www.signalpro.biz for our experince with MEMS related issues.

Impedance matching: An example

Impedance matching is a key task in RF design and and also in lower frequency design where power transfer is an issue. A number of techniques exist to do this. Some are built-in scripts for advanced CAD programs while other techniques are manual. One of the techniques used quite commonly is the L - Section impedance matching technique. It is of interest to examine this technique. A recent technical memorandum released by the techteam at Signal Processing Group Inc. describes in some detail the matching of an antenna impedance and a resonant circuit associated with the antenna. It shows the detailed development of the matching circuit and checks that can be made to evaluate it. A PSPICE simulation is also shown along with the .cir file and plots. Interested readers are directed to the SPG website at http://www.signalpro.biz > "Engineer's Corner" for details.

The quarter wave matching transformer

In many high frequency applications matching a transmission line of known impedance to a known resistive load is an operation that is done over and over again. A simple way to do this is to use a quarter wave transformer. This concept is explained more fully in a paper released by Signal Processing Group Inc. recently. Interested readers may access this at the "engineer's corner" in the SPG website located at http://www.signalpro.biz.

Series to parallel conversion of LCR circuits

In a number of applications, specially in impedance matching LCR circuits may undergo series and parallel conversions. These conversions leave the performance of the circuit unchanged. They simply change the configurations to provide for a more appropriate architecture for the operation ( whatever that may be). A simple paper released by Signal Processing Group Inc. describes a method to do this. Interested parties may go to the website at http://www.signalpro.biz and access the paper from the "Engineer's Corner".