Passing on another non-member post...... Jim
>>> "Hight, Kevin" <[email protected]> 10/14 7:16 PM >>> > IEEE EMC SOCIETY > > ROCKY MOUNTAIN CHAPTER > > OCTOBER MEETING > > TUESDAY OCTOBER 20, 1998 > > Mr. Robert W. Dockey > Hewlett-Packard Company > > "New Techniques for Reducing Printed Circuit Board > Common-Mode Radiation" > > WHERE: NIST - Boulder > 325 Broadway > Boulder, Colorado 80303 > > TIME: 7:00 p.m. > > DIRECTIONS: From Denver take I-25 to Highway 36. Go NW on Highway 36 to > Boulder. Continue on Highway 36 to Baseline Road. Take Baseline Road > West one block to 27th Way. Turn South (left) on 27th Way and continue > past Broadway into the NIST parking lot. Enter through the Main doors > (facing Broadway) and check in with the guard at the front desk, the guard > will direct you to our meeting room. > > DINNER: 5:30 p.m. - 6:45 p.m. Rafferty's Restaurant > 2805 Pearl, Boulder, Colorado 80301, Phone; (303) 447-2665 > Rafferty's is on the corner of 28th (Highway 36) and Pearl. From > Baseline road, continue North on Highway 36 (28th Street) 5 stop lights. > Take next Right into the parking lot of Rafferty's. See you there! > RSVP to Kevin Hight at 303-417-5534 by noon on the 19th. > > For more information please contact one of the IEEE Rocky Mountain Chapter > EMC Society Officers listed below. > Chairman: Jeff Doolittle 303-449-4165 > Vice Chairman: Joe Kramer 303-449-4165 > Secretary: Kevin Hight 303-417-5534 > Treasurer: Wes Smith 970-962-7472 > > EVERYONE IS WELCOME ! > > > AUTHOR BIOGRAPHY > Robert Dockey > Bob is the EMC Engineering Group manager at the Hewlett Packard division > in Vancouver Washington. He has a BSEE from the University of Missouri at > Rolla and is certified as an EMC engineer by the National Association of > Radio and Television Engineers. He is the author of three technical papers > on various EMC subjects and is a member and Distinguished Lecturer of the > IEEE EMC Society. > > Bob has been with Hewlett Packard for 13 years as both an EMC engineer and > engineering manager. Previously, he spent 13 years as a TEMPEST > engineering manager for TRW in Colorado Springs, Colo. > > > > INTRODUCTION > Have you ever had the experience of believing that you had done everything > humanly possible to reduce the radiated emissions from an unshielded > printed circuit assembly and yet still measure unacceptable margins? If > so, this presentation could help explain the reasons why. Even when all of > the common emission suppression measures like power supply decoupling, > cable filtering, loop area control and full ground planes have been > utilized, there is still one dominant coupling mechanism remaining which > can be manipulated to improve the margin. Unfortunately it may also set a > lower limit on the possible emission level which can be obtained from a > specific design. This mechanism is referred to as "Ground Plane Voltage > Gradient" contamination. This presentation will attempt to describe and > analyze this radiated emission mechanism and present several design > techniques which can be used to deal with it successfully. > > "New Techniques for Reducing Printed Circuit Board Common-Mode Radiation" > ABSTRACT > A multi-layer printed circuit board with a "good ground plane" can produce > common-mode radiation similar to a dipole antenna. This ground plane is > commonly thought of as a low impedance path for returning currents and one > which is of constant potential across its area. In fact, these currents > give rise to voltage gradients in the plane which act as sources of > common-mode current. The majority of the RF current flowing along a signal > trace on a multi-layer printed circuit board (PCB) returns on the ground > plane directly beneath the signal trace. However, a small portion of the > ground-plane current also can return via indirect paths causing the PCB > and attached cables (if present) to produce common-mode radiation similar > to a dipole antenna. Several new techniques to reduce these emissions by > lowering the inductance of the ground return or by bypassing the > common-mode current on the cables are presented. These cost-effective > techniques can be employed on two-sided or multi-layer PCBs. > Previous independent work by German, Ott and Paul experimentally > investigated the radiated emissions from a printed circuit board (PCB) > with a digital circuit that produced current on a signal trace that > returned via an adjacent ground-return trace. They demonstrated that if > this two-wire transmission-line is slightly unbalanced, it will radiate as > an asymmetric dipole antenna producing common-mode radiation at much > greater levels than the differential-mode radiation from the current loop. > A direct prediction of this radiation was later performed by Hardin, Paul > and Naishadham. > > In 1993, Dockey discovered that a relatively small PCB with a solid > ground-plane could also produce common-mode radiation. On this truncated > Microstrip transmission-line, the majority of the signal-trace current > returns on the ground plane beneath the signal trace. However, this > current encounters the finite inductance of the ground plane and produces > a voltage gradient. The voltage gradient, commonly called the ground-noise > voltage, then causes a small portion of the signal-trace current to flow > through the distributed stray capacitance of the ground plane. > > This presentation will elaborate on these findings and propose several > methods which can be used to effectively mitigate the radiation > mechanisms. > > > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
