Manchester decoder technique and circuit

Manchester codes are popular protocols for data transmission over both wireless and wireline communication systems. The technique consists of a encoder and a decoder. Of the two, the decoder is more of a challenge. There are a number of ways of implementing a manchester decoder. We think the simplest way to do it is using a completely digital technique. This technique is described in a recent brief note from Signal Processing Group Inc. The paper can be found at http://www.signalpro.biz under the Engineering Pages menu item.

VSWR, its relationship to return loss

The voltage standing wave ratio and the return loss ( and its related quantity, the reflection coefficient)are all related to each other. Once any one of these can be calculated, measured or simulated the others can be derived. These quantities become specially important in the case of matching network design ( as in Rf Power amplifiers for example). A brief paper by the technical team at Signal Processing Group Inc., describes this. The paper may be found at http://www.signalpro.biz > Engineering pages by interested readers.

Classes of RF Power amplifiers and when to use them

RF power amplifiers come in multiple classes. A, B, C, D, E,F etc. Some of these are highly efficient but more non-linear. The Class A amplifier for example is very linear in operation but dissipates a lot of DC power. In order to understand the advantages and disadvantages of each, it is useful to study the characteristics of these types of amplifiers. An interesting paper was found in the literature which in our opinion is a good one for the student of RF amplifier classes. The reference is provided below for interested parties. " RF Power Amplifiers, Classes A through S -- how they operate, and when to use each". By, Sokal, N.O. Design Automation, Lexington, MA, USA. Published in the Electronics Industries Forum of New England, 1997, Professional Program Proceedings, Boston, MA. 6 -8 May, 997. pp 179-252.

Emitter degeneration effects in common emitter amplifiers

A technique used in the design of common emitter amplifiers, both to increase input impedance and bandwidth, is emitter degeneration. This consists of inserting an unbypassed series resistor from the emitter of the bipolar to a common point ( ground, virtual ground, etc.) The impact of this method on the circuit performance is explored in a recent brief publication by Signal Processing Group Inc. The paper may be found at http://www.signalpro.biz>Engineer's corner.

Impedance matching differential circuits

L-Section impedance matching is a popular and simple technique. The basic principle is a single ended input to a single ended output. However, if one has differential inputs and outputs, a way has to be found to convert the single ended matching configuration to a differential configuration. A recent brief paper by Signal Processing Group Inc., addresses this issue. It can be accessed by interested parties at http://www.signalpro.biz >Engineer's corner.

Low voltage modified Gilbert cell mixer: An addendum

This brief note is an addendum to an earlier post on a low voltage modified Gilbert cell mixer. If the power supplies ( VCC ) do not vary too much ( typically 5%), then the low voltage mixer can be used as is. However, if the power supply variation is greater ( say 3.0 to 6.0V ), then the earlier design's current dissipation will be uncontrollable. In such a case it is best to revert to the standard Gilbert cell mixer. The saving grace is, that if the design is being done in a Bi-CMOS process, then instead of using a bipolar as the tail current in the mixer, a MOSFET can be used. Note that in this case the drain to source voltage of the MOSFET can be very low ( VDS=0.1V or lower) depending on size. In this case the power supply voltage will have a minimal impact on the current dissipation.

A low voltage modified Gilbert Cell mixer.

RF mixers are workhorses of many RF/wireless designs. There are a number of types in use. Many are passive ( diodes, CMOS quads, etc) and some are active ( single balanced, doubly balanced). A ubiquitous design is the Gilbert cell mixer. It is doubly balanced, provides gain, can be implemented simply in ICs. However, when it comes to low voltage operation it causes issues. Therefore a number of modified Gilbert cell mixers have been proposed. Among them is the mixer described in a recently released brief by Signal Processing Group Inc. Please access it at http://www.signalpro.biz>engineer's corner. For further details and discussion please contact the author at spg@signalpro.biz.