Radio signals suffer a path loss in free space ( as well as in other media). Recently a brief article was released by SPG technical staff which provides some simple expressions for the calculation of this free space path loss These expressions are useful in quick calculations of received power at a close in distance for an antenna. Using these expressions, and the formula for calculating the induced voltage in an antenna as a result of the received power, is a starting point for more sophisticated calculations. This paper can be found at http://www.signalpro.biz >> engineer’s corner.
In certain analog ICs it is necessary to have very high input impedance and very low base currents. For such applications, the typical current gains of an integrated npn transistor are not high enough. It is possible to increase the current gain of an npn transistor significantly by improving the base transport efficiency. In this case the base is very narrow ( a few hundred angstroms or less). The collector to emitter breakdown of a structure like this is relatively low ( 2V – 3V) because the collector base depletion layer can punch through the active base region into the emitter. This is the punch-through or “super-beta” transistor. Current gains of 5000 are obtainable using this technique at currents of 20uA or so with a Vce of around 0.5V. The fabrication of super-beta transistors in a standard process can be done by using one extra masking step and diffusion. After the base diffusion for the normal NPN transistors a special mask is used to open up the emitter diffusion for the super-beta transistors. At this stage the emitter of the super-beta transistor is only partially diffused.This step is then followed by the masking and n+ diffusion of the standard npn. Owing to the extra diffusion step for the super-beta transistor, the emitter of the super-beta transistor is diffused slightly deeper
than the normal npn resulting in a narrow base width.
Recent needs in low power and single battery ( 1.2V) design demand a power converter circuit. A recent requirement for a handheld FM receiver ( multichannel) necessitated
the design of a voltage supply converter using off the shelf devices. After a thorough search for off the shelf devices which could be used to realize such a converter a device was chosen from a popular manufacturer and the design was started. Here are some issues that we encountered, ( perhaps not new, but nonetheless need to be mentioned). Our biggest challenges, suprizingly enough had very little to do with the IC that we used. This was because the vendor had excellent technical support and application notes and had a well organized technical support environment. Our requests were handled within a 24 to 48 hour turnaround. The challenges that were difficult had to do with selecting, acquiring and using the passive components. These were harder to find and technical support left much to be desired. In spite of these issues we managed to finish the design in time and test the board. It worked quite well and provided 3.3V at close to 1.0A and 5.0V at close to 0.5A as needed with a 20% margin. Interested readers are invited to contact us through our website at http://www.signalpro.biz.
A visit to Germany and Switzerland was fruitful with some interesting ways the Europeans are using wireless technology. As elsewhere, wireless is being used in almost every restaurant to bill smart cards and credit cards tableside. An interesting application of wireless was encountered in the dairy farming industry where the use of wireless enabled bolus’ monitor health and various other states of cows and other farm animals. This is different from RFID that is used in identification. An interesting aside to this is the fact that there is very little data available on the propagation loss of a radio signal through living tissue ( in bovines and other species). Frequencies are not really standardized. There is a European standard but it appears that vendors are still using their own specifications. Happy new year to all!