Saturday, May 18, 2013

IC design: Impedance matching diiferential 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 >Engineer's corner.

Saturday, May 4, 2013

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 effect on the performance.

Thursday, May 2, 2013

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>engineer's corner. For further details and discussion please contact the author at