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".

IC design and reliability: Failure distributions and the FIT

The failure rate for ICs is defined by: (Number of devices failed/Total number of devices tested)(1/time). The units can be stated as failures per device hour. This is an important parameter and has to be considered as early as possible in the design of the device. A unit called a FIT can also be defined. In this case a FIT = one failure per 1 billion device hours of operation. A FIT can be used to evaluate devices and distributions. The simplest model of failure is given by the parameter called the mean time to failure or MTTF. MTTF = 1/KF. Here KF is simply the failure rate per unit time. This is used in the exponential model which is very popular. The exponential model is simply expressed as: Fail(t) = 1.0 - exp(-KFt). This model is easy to use and calculate and can be used to assess the design of the device based on a failure rate model. Data is usually available from foundries for the use of this model. Please visit our website at http://www.signalpro.biz for more ASIC and module design and manufacturing information. Please contact SPG for detailed information on more extended types of failure expressions and their use in the design of devices. i.e how these failure parameters mesh with design parameters that allow the design to be more robust in terms of MTTF or failure rate.

IC design for mini(TM) and macro(TM) ASICs

We have divided the ASIC types that we develop into two categories. These are the miniASIC and the macroASIC. This nomenclature applies to the functionality, size, complexity and cost of the device. A miniASIC is a device with very few elements on it. It is small in size ( remember size differentiation; 50 mils on a side is small, 100 mils on a side is medium and 250 mils+ on a side is large for analog, RF, wireless or mixed signal ASICs). Examples are: 2 power/high voltage MOSFETs, a closely matched high frequency differential stage, multiple bipolars or MOSFETs on a chip (used largely for bread-boarding and proof of concept sometimes. Although these can be valuable adjuncts to a board design in production as well.) A low logic gate device, more logic gates than a CD4000 series device perhaps, but less than a large digital design ( 5k gates+). Matched resistors, capacitors, inductors and interconnect on a chip. A macroASIC on the other hand lies at the other end of the spectrum. It is a larger device,(definition above), it is more complex and costs more. In our experience both types come in handy when developing systems. The miniASIC can be used as part of glue circuitry ( when the exact device you need is not available of the shelf and it has to be cheap). The macroASIC is the device of choice when you want to sweep many discrete components on to a piece of silicon ( or GaAS, SiGe, GAN, etc)to provide enhanced performance, reduction in cost, safety of R&D, increased reliability and manufacturability, testability, and so on. Signal Processing Group Inc., provides both types of devices. The only drawback is of course that you cannot just go out and buy something quickly off the shelf. Lead times for these ASICS is of the order of 2 to 10 weeks. However, if the planning takes this into account then mini and maro ASICs become a sound choice. Please visit our website at http://www.signalpro.biz for more info.

Image reject mixer: A detailed explanation of operation

Image reject mixers are interesting circuits used in RF/wireless receivers to avoid the problems associated with the image frequency. ( To read about the image frequency please search for "image frequency" in this blog). A recent white paper from Signal Processing Group Inc, examines the operation of the image reject mixer and provides a fairly detailed explanation of the operation for interested readers. Please visit our website at http://www.signalpro.biz > Engineer's corner

Dot rule for magnetically coupled circuits ( baluns and transformers)

In a magnetically coupled circuit like a balun or a transformer the phasing of currents and voltages is commonly indicated by the dot rule. Place a dot at either end of the primary. Drive this end positive ( for example). Measure the voltage at the secondary ends. The end of the secondary which is also positive ( or generally in phase ) with the primary end is also indicated by a dot. The other end of the secondary will be 180 degrees out of phase. Current flowing into the dotted terminal at the primary end will cause the current to flow out of the dotted end of the secondary and vice versa. Visit our website for more information and articles of interest at http://www.signalpro.biz.

VSWR control on chip

High levels of mismatch, for example in a transmitter or any output power device, can sometimes cause catastrophic failure of the device and its associated subsystem. Depending on the application this can be a severe problem. An interesting approach to prevent or control these types of failures is the use of an on chip integrated power detector. The power detector is used to estimate reflected power and if the VSWR (matching) gets really bad ( due to aging, component failure or other such causes) the power detector either signals a problem before the it reaches irreversible levels, or executes automatic control of VSWR. Please visit our website at http://www.signalpro.biz for other interesting articles or just information.