Sunday, July 29, 2012

PLL ( Phase locked loop) design and simulation using Analog Devices freeware tool.

We have been looking at various RF/Microwave design freeware tools recently. One of the tools that we looked at closely is the Analog Device ADsimPLL tools. This allows the design of PLLs and synthesizers using AD's devices which come pre-programmed in the software. The tool is interactive and fairly intuitive and user friendly. There are of course, a few challenges but considering that one pays nothing for its use it is well worth the time spent on analyzing and using it. We designed a 1.83 Ghz loop using the AD4360-7 device. The tool allowed us to calculate the various PLL related component values and provided a quick assessment of the operation both visually and textually. We would have liked to see some additional small features in the tool but all in all our assessment of the tool is quite positive. For further information on this or on PLL design activity at SPG, please visit our website at and use the contact menu item for any further discussions or questions on our experience.

Sunday, July 22, 2012

Estimating the signal band noise in delta-sigma modulators

Sigma delta modulators are popular devices used in a multiplicity of applications. One of the most prolific of these is the A/D converter. A delta - sigma A/D basically consists of a delta-sigma modulator ( typically first or second order), followed by a decimation filter. The modulator operates in such a way that it generates a high pass response for the noise in the system. This response is known as the NTF or noise transfer function of the modulator. In this way the modulator suppresses noise within the passband but allows the out of band noise components to have a high pass characteristic. A low pass system of decimation filters removes this latter noise also. It becomes imporatnt,in the practical sense, to estimate noise in the passband. An expression can be developed to do this for higher order modulators with fairly accurate results. This subject is dealt with in a recent brief paper released by Signal Processing Group Inc. It may be found in> "engineer's corner".

Thursday, July 19, 2012

RF/Wireless design freeware

A survey using search of RF/Wireless/MMIC freeware on the web led to a nice harvest of freeware routines that provide useful tools for those of us who may want to use these types of programs. It is well known that a number of EDA companies sell fairly expensive RF/Wireless/MMIC programs. For many designers it may be difficult to buy these because of the cost. For these users the freeware that is available on the web might be a partial solution. The freeware programs are not as beautifully formatted but appear to be reasonably accurate when compared to results provided by the more expensive packages. An ongoing interest for us is to take a look at these freeware programs and assess their usefulness and price/performance ratio. A useful package distributed free by Agilent is the first on our list. It is called "appcad" and may be downloaded free. Apart from the marketing type information in this package a number of useful tools are included. It certainly deserves a close look.

Tuesday, July 17, 2012

SINAD: What is it and why is it important?

SINAD is figure of merit typically for radio receivers or similar devices. It may also be used in other applications. SINAD compares the signal power, the noise power and distortion power of signals. The specification is usually used in an audio sense. i.e the quantity under consideration is the quality of the received audio. A report on SINAD, its definition and other related parameters is available in the Signal Processing Group Inc., website at > engineer's corner for interested parties.

Logarithmic amplifiers ( LOG AMP): A very useful component.

Logarithmic amplifiers or Logamps as they are commonly called are very useful components. They are used in communications, RF and wireless systems, cell phone base stations, audio systems, and power control to name a few application areas.. A typical use in RF/wireless is in the RSSI ( received signal strength indicator) circuit. The logamp can be deceiving in its functionality so a basic description is of help for those who plan to use it. A paper on this component and its basics is available on the Signal Processing Group Inc. website under the "engineer's corner" menu item.

Thursday, July 12, 2012

Design considerations for integrated circuit RF/MMIC power amplifiers

Integrated circuit RF/MMIC power amplifiers are getting more and more popular. The PAs can be standalone or part of a larger device. Multiple technologies exist for the implementation of the circuits from CMOS to III-V. For the designer of these circuits different technologies present different challenges. In a brief paper by Signal Processing Group Inc., technical team, some of these issues are explored in a cookbook fashion. The paper may be found in the SPG website at>engineer's corner.

Sunday, July 8, 2012

What in the world are Hogenauer filters?

Hogenauer filters are sometimes better known as CIC filters. This begs the question: What on earth are CIC filters? CIC stands for "cascaded integrator-comb ". These filters are used very often as sigma - delta A/D decimation filters and the inverse ( interpolators ) are also used in image processing and other applications. These are examples of multirate filters.

Eugene B. Hogenauer published the principles of these filters in his paper entitled:
" An Economical Class of Digital Filters for Decimation and Interpolation", IEEE Transactions on Acoustics, Speech and Signal Processing, Vol ASSP-29, No. 2, April 1981.

These filters came to be known as Hogenauer filters. CIC is just another name for the structure he proposed. That I believe answers the fundamental question posed in the title of this post.

We decided to investigate these filters a little more in an attempt to demystify the mathematics and the structures so they would become more friendly to us practising engineers. In the attempt perhaps also come up with a few useful formulas or graphs or tricks for usage.

The result of this work is detailed in our wesbite at>engineering pages>hogenauer filters. Interested readers may peruse this interesting paper at their convenience.

Saturday, July 7, 2012

Analog and mixed signal design: Thermal management of device dissipation

More and more thermal management is required for current analog devices as power dissipation levels climb. In some devices such as power amplifiers, LED drivers, DC - DC converters and other higher power devices, the problem is so obvious as to sometimes burn one ( and not just metaphorically speaking) in a significant manner. The demonstration of the Dell laptop which burst into flame not so very long ago was a vivid demonstration of what we as design engineers have to live with. Its not just the power devices that need thermal management. A cooler device will run better in many environents so even lower power devices need thermal management. A PCB with various power level devices mounted on it needs thermal management. In spite of these reasons thermal management is not as well understood as one would expect. This post is an attempt to bring attention to, and provide some useful information for thermal management. In a recent report released by Signal Processing Group Inc, to be found at, information and resources can be found by interested parties. Please go>engineer's corner and access the thermal management articles.

Friday, July 6, 2012

Quadrature detection in FM

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

Monday, July 2, 2012

Image frequency in RF/wireless circuits

The image frequency in Rf/wireless receivers is an issue that has to be understood by radio designers and tackled for robust design. The image frequency is a so-called spurious signal which can cause a number of bad effects.Its origin lies in the mixing of multiple frequency signals in the receiver mixer. A paper released recently by Signal Processing Group Inc., describes this effect in simple terms so that an understanding of the effect may be obtained by interested designers. The paper can be accessed in the engineer's corner at

Sunday, July 1, 2012

Difference between, ASIC, an analog ASIC, a rf ic or a MMIC

There are a number terms that are used frequently to describe the various forms of semiconductor devices used in the industry. An ASIC is one of them. Other terms are rf ic/ wireless ic, an analog ASIC, a MMIC and so on. So what are the differences between these devices? Ultimately all of these devices are semiconductor integrated circuits, indicated by the ic ( or integrated circuit abbreviation). However there are some differences between the various forms of these integrated circuits that lead to the differing nomenclature. Generally if there is no descriptive abbreviation before or after the "ic", then an ASIC is considered to be a digital device consisting of logic gates, digital memories, microprocessors or microcontrollers and associated circuits all integrated on to a relatively large piece of silicon. An analog ASIC or an analog ic is usually made up of mostly analog circuitry such as amplifiers, comparators, A/D converters, D/A converters,operational amplifiers, analog comparators, voltage references, regulators, etc. A pure analog ASIC or ic operates in the analog domain. It is usually smaller in size than a typical digital ASIC. An rf ic is distinguished by integrated circuitry such as transmitters, receivers, PLLs, modulators, frequency multipliers, rf amplifers, rf power amplifiers, mixers, inductors, transformers, baluns etc. An rf ic also operates at higher frequencies ( typically up to 1 Ghz). A mmic is a monolithic microwave integrated circuit. It may have the same type of circuitry as an rf ic but the frequencies of operation are much higher that rf ics. Currently mmics may be found operating at frequencies in excess of a 100 Ghz. A further type of device referred to as a mixed signal ic has both analog and digital circuitry on it. Sometimes the digital ciruitry is dominant sometines the analog circuitry is dominant.

What is an ASIC? Why use it?

ASIC stands for "Application Specific Integrated Circuit". This means that an ASIC is designed to be used in very specific applications. Another term for it is "custom" chip. For ASICs a customer specifies certain requirements and specifications and the ASIC supplier then designs to those specifications and supplies the ASIC to the buyer. As such, ASIC has become a generic term. The usage of ASICs has become popular owing to a number of features that ASICs offer. First, the ASIC is usually very small. So it saves space on a board or enclosure that the customer may be using. In some cases there is no way out for the customer,but to use an ASIC. This may be the case, for instance for hearing aids, watches, cell phones. ( Although, strictly speaking a cell phone uses a lot of standard devices in addition to ASICs).An ASIC can be a great cost reduction tool.Insertion costs, discrete device costs, manufacturing costs and other associated costs csn be saved by using ASICs. An ASIC is a very useful tool when it comes to hiding intellectual property ( IP). Most of the circuitry is inside a very small package and can be made to be almost impossible to reverse engineer. Obviously a well designed ASIC can also increase reliabity significantly. No wires to come loose, nor connectors to fail etc. All in all an ASIC can be very useful indeed. To read more about designing an ASIC for yourself please see the article in this blog.