Metastability in Flip Flops and logic circuits

Many faults in digital circuit design, specially those using flip flops can be traced to the phenomenon of metastability. It is something that for a long time was not even recognized as an error source. However, a number of design engineers including the author of this article have personally experienced the tragedy of logic failure owing to metastability. In most instances the failure is hard to spot and can take its toll on the engineer trying to debug a malfunctioning logic circuit. Sometimes the problem is made even more catastrophic because the circuit may function quite well under certain conditions and fail under others. It can literally drive the design engineer up the wall! In analog and mixed signal design, whether it is a lower frequency circuit or a higher frequency circuit the causes and effects of metastability remain about the same. For those readers who may have experienced this and wish to investigate further, please review the paper on metastability in the “Engineer’s Corner” in the Signal Processing Group Inc., website located at

Quadrature detection for FM signals

Quadrature detection of FM signals is a well known technique that has been used for a number of years. It uses phase shifting and multiplication of signals to detect FM modulation. A recent whitepaper by the techteam at Signal Processing Group Inc., describes this type of detection and presents an analysis for the more technically minded. The paper can be accessed at the “Engineer’s Corner”, in the SPG website located at

The ISM band: A review of the essentials

In 1985 the Federal Communications Commission issued rules permitting “ intentional radiators” to use the “ Industrial, Scientific and Medical (ISM) Bands ( 902-928, 2400-2483.5, 5725-5850 Mhz) at power levels of up to one Watt without end-user licenses. Originally these bands had been reserved for unwanted, but unavoidable emissions from industrial and other processes, but they also supported a few ( often military) communications users. The new rules led to the development of a large number of consumer and professional products and is considered to be an important step towards the development of wireless computing or multimedia applications. Applications in the ISM band include, wireless LANs, short range links for advanced traveller systems ( electronic toll collection), garage door openers, home audio distribution, cordless phones, private point to point links, remote control, wireless telemetric systems ( e.g electrical power consumption monitoring) etc. Applications seem to be limited by the imagination rather than technology. A drawback of the ISM band is lack of any protection against interference. In particular microwave ovens limit the useful range of such communications devices. The techteam at Signal Processing Group Inc. recently released a brief whitepaper on the ISM band. Interested readers can find this under the “Engineer’s Corner” menu item in the SPG website located at

Analog and mixed signal design: Opamp offset voltage

The DC offset voltage of a differential amplifier is an important parameter for most opamp applications. It also impacts the CMRR of the opamp. In most cases for simple applications the offset voltage of a simple opamp may be perfectly satisfactory. 1 – 5 mV for bipolar designs , 20mV to a 100 mV for CMOS designs. However, when the application is more stringent, very much lower offset voltages are required. In this case special techniques to reduce the offset voltage of the differential amplifier are used. A recent brief article about DC offset voltages released by Signal Processing Group Inc., is available for review in the “Engineer’s corner” located in the the SPG website at For further help please contact Signal Processing Group Inc., directly at

Transmission line stubs and microwave distributed filters

As frequencies rise in MMIC or high frequency design ( board or chip) lumped elements cannot be used for implementing filters. In this case a technique that is useful is the use of transmission line stubs. The use of these stubs leads to microwave filters which are practical (with a few constraints). These types of filters and the methods of implementation are discussed in a recent release of a technical memorandum by the Techteam at Signal Processing Group Inc. Interested readers may access this article at , in the “Engineer’s Corner”.

PCB electrical and thermal parameters for design

PCB design is not only a science but also an art, as every PCB designer knows. However, the art of design is predicated by the science to a certain extent and in order to do a good job a designer has to know certain parametric effects of PCBs. A recent whitepaper released by Signal Processing Group Inc., offers a brief treatment of the first order electrical and thermal parameters for PCB design that can be useful in PCB design, both for understanding, as well as robustness of design. The paper can be accessed via the “Engineer’s corner” menu item in the SPG website located at

How many times did Thomas Edison fail?

A light hearted post. Having read a number of books, both on Thomas Edison’s life as well as motivational we have come to the conclusion that no one really knows how many times Edison failed before he got his first light bulb working. Here are the different numbers so far: 6000 times, 11000 times, 21000 times, 1000 times, 10000 times and an astronomical 56000 times!! Perhaps someone out there has other numbers they might want to share with us. We can be contacted on our email at:

Analog design entrepreneurs alert

This post is not engineering-centric.It is addressed to engineers who may have the entrepreneurial bug. Times have changed so much that there are new opportunities for people who have a developed product and want to profit by their efforts with little or no money expended. The online/cyber world has had a tremendous impact that could not be imaginged only a decade ago. Then an engineer with a product had very few avenues open to him/her to gain from it financially . Today there are a myriad of ways that can be done. For more information about these techniques please contact Signal Processing Group Inc., via the “Contact” menu item in the website located at