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Archive for RF Design

Multiphase 48 Volt Conversion for Low Noise Applications in an Instrument Grade Power Supply

RF Design•on February 4th, 2011•No Comments

Introduction

During test, today’s high-speed integrated circuits require power supplies with lower voltages and much higher current than previous generations. Already, high-end devices use 0.8 to 2.0 V and up to 300 A. Automatic Test Equipment (ATE) instruments used to measure device under test (DUT) performance during design verification and production testing must have power systems that meet the following requirements:

•  High force voltage accuracy (1 mV or less)

•  Quick response time to load current changes (less than 1 µs)

•  Low noise levels (less than 10 mV)

•  Very high current capability (up to 300 A)

The problem is that power supplies currently used in the ATE industry do not meet these requirements.

One possible way to achieve the desired performance is to use a custom designed linear regulator. A linear regulator can meet the accuracy, current response time, and noise level requirements. However, its power dissipation can cause problems with heat dissipation, component selection, and area utilization if the input DC level is too high compared to the output voltage.

For different parts being tested, the desired output voltage varies, so choosing a fixed input voltage is difficult. Since the performance of the linear regulator is a function of the difference between the input and output voltages (overhead voltage), one way to minimize these problems is to use a switching power supply as the input to the linear regulator. The switching power supply provides a constant overhead voltage for the
linear regulator from the 48 V distributed to the test head. [13]

The following figure shows the power distribution system for an ATE test system.

Power Configuration of a Large IC Test Instrument

Figure 1. Power Configuration of a Large IC Test Instrument

The switching power supply in this application must meet the following requirements:

•  High current output – The power supply must support the linear regulator’s output.

•  Fast response – The power supply must adjust quickly to large output voltage demands and transition between low and high currents with minimal variation in the overhead voltage presented to the linear regulator.

•  Low noise – The power supply must minimize conducted noise on its output path to the linear regulator. It must also minimize all forms of radiated EMI noise that could degrade the accuracy of the linear regulator.

The major difficulty with using any switching power supply in a precision DUT power supply is high-frequency parasitic ringing at the edges of the switching waveforms. That ringing creates noise that interferes with the linear regulator. [12, 13]

This paper focuses on ways to minimize that noise in a switching power supply design that implements a 48 V input voltage, multiphase, zero-volt switching, and phase control. Note that not all potential noise sources are discussed in this paper, including common mode noise, capacitive coupled noise, magnetic noise, and radiated noise.

The major features of the proposed switching power supply design focus on the most critical design priority – reducing high-frequency parasitic ringing noise:

•  A transformer is needed because of minimum pulse width requirements and the range of adjustable output. The construction of the  transformer is flat planar windings for minimized leakage inductance. [1, 3, 8, 12]

•  A full-bridge with zero-volt switching for the primary control of the transformer is used. Soft switching minimizes energy for ringing and phase control allows a consistent gate drive. [2, 4, 7, 11]

•  Multi-phase circuits are implemented to enable maximum response time. This design uses the maximum number of practical phases. [7, 9, 10]

•  A dual Schottky diode and a center tap output for rectification is used for the output stage, which limits the number of fast switches. The output stage proximity to the end user drives this decision. Gate drives are one of the highest noise producers, and this limits the number of gate drive circuits. [5, 6, 12, 13]

•  The Schottky diode package also limits the output stage to 40 A.  The most practical package under the cold plate is a TO-247. The largest dual diode in a TO-247 is 40 A. This fixes the maximum current per phase and the number of phases.

•  Ferrite beads are used extensively on all switches to control ringing. [5, 6, 12]

To verify these design concepts, we designed two switching power supplies for use in an ATE environment.

•  The first generation power supply has two outputs at 2.5 to 8.5 V @ 720 W per output with peak power at 4.5 V and 160 A.

•  The second generation power supply has two outputs at 2.5 to 6.0 V @ 380 W per output with peak power at 4.5 V and 85 A.

The following sections summarize the major issues for reducing noise in these switching power supply designs.

Transformer Construction

We investigated two forms of transformer construction:

•  Flat planar construction of interleaved coils

•  Copper straps over a single primary winding method

The following figure shows the effect of the transformer construction noise. These waveforms indicate that the flat planar construction is the least noisy choice. [1, 3, 8, 12]

Output Voltage of Transformer Using Two Construction MethodsFigure 2. Output Voltage of Transformer Using Two Construction Methods

Using Amorphous Beads on Output Diodes and Ferrite Beads on FETs

We also examined how using amorphous beads on the output diode leads and ferrite beads on the FET leads affects parasitic ringing. To observe these effects, we took measurements at the output diode and the power supply’s output voltage. [6, 12, 13]

Figure 3 shows how using beads can effectively eliminate parasitic ringing at the output diode.

Parasitic Ringing at Output Diode

Figure 3. Parasitic Ringing at Output Diode

Figure 4 shows how using beads reduces parasitic ringing at the switching power supply’s output voltage. Note that the AC waveforms shown in these figures do not reflect all the noise elements, but they help illustrate the differential noise of the output and its frequency content. 

AC Waveform of Parasitic Ringing on Power Supply Output Voltage
Figure 4. AC Waveform of Parasitic Ringing on Power Supply Output Voltage

Conclusion

The reduction of noise at the linear regulator output demonstrates that the switching power supply design met the performance requirements described in this paper.

The linear regulator output exceeded the 1 mV accuracy requirement, maintained noise levels of less than 1 mV, and achieved all of the dynamic response requirements. The only drawback of this design is that the output diodes now require cooling. However, by using all known methods to reduce switching power supply noise, ATE test system designers can now implement linear regulators that meet requirements that have not been achievable in previous power supply designs.

Marine Obstruction Warning System

RF Design•on July 16th, 2010•1 Comment

Eclipse Design Technologies has undergone a new project called the Marine Warning System. The purpose of the Marine Warning system is to highlight obstructions in the water for vehicles navigating through waterways. Along with making the product cost-efficient, the design must be aesthetically pleasing, highly visible a night, easily mountable, and water tolerant.

To complete the design, requires advanced electrical and mechanical engineering. The electrical component of the design involves a string of LED lights running through clear tubing that are wired to D-cell batteries and connected to a photoelectric diode. The photoelectric diode allows the device to only be used when there is not enough light for the boats to see the obstructions. The biggest electrical problem that occurred during the design was improving the battery life without using too many batteries. To solve this, we used 4 D-cell batteries, wiring 2 in series with the other 2.

The mechanical piece of the project entails finding a suitable and cost effective way to waterproof the electrical components as well as developing a way for the system to attach to the obstruction. The waterproofing was done using a modified plastic, waterproof case that allows the tubing to run into it and still keep the electrical components dry. The whole system is then attached to the obstruction using a Velcro strap that is attached to one end of the tube and runs through a handle on the waterproof case. The biggest mechanical problem that occurred during the design was modifying the waterproof case while keeping the inside dry. This was solved by using a seat washer that allows the tubing to run through while creating a seal on the inside and outside of the hole as well as a tight seal on the tube.

If you have any comments on this design or the many others that Eclipse is currently under contract for-please reply.

Mil/Aero & ASIC design services

RF Design•on May 8th, 2010•No Comments

May 5th, 2010: For Release:

Eclipse has partnered recently with Dimation, Inc of Burnsville MN. USA. a strong player in teh Military and high reliability manufactruing  and quick turn support space.

Key services include 24 hour turn around of PCB & full turnkey manufacturing, repair services, and Die Level Services such as;
Gold/Aluminum Wedge Bonding
Gold Ball Bonding
ultra fine pitch  solutions for < 35um
Chip Scale Packaging
Stacked Die
MCM Packaging
Die Inspection  
Wafer Sawing
Waffle Packaging
Custom Packaging
TSOP~QFN~MLF~SOIC
And many others…

To view their capabilities, please go to http://www.dimation.com/capabilities.html

Class II and III
ANSI/J-STD-001 Certified

RF Design with NextGen wireless LTE

RF Design•on April 6th, 2010•No Comments

David Mitchell, Presidnet of NEXT GEN Wireless says his company has the ability to now do LTE design.

” We are now well versed in designing for 4G and beyond”, says David. recently read an article that may help clarify this, see below”…

Gadget Lab Hardware News and Reviews

WiMax vs. LTE Battle for Next Gen Wireless Heats Up

  • By Priya Ganapati Email Author
  • March 6, 2009 |
  • 11:11 am |
  • Categories: Wireless Tech

The Clear WiMax wireless broadband connectivity service from ClearWire has been available only in Portland and Baltimore so far but the company has some big expansion plans up its sleeve.

ClearWire plans to extend its WiMAX service to about 80 cities nationwide by the end of 2010. WiMAX subscribers will get a 3G/4G modem, says the company, but its not a home run yet for Clearwire. Rival Nokia is ramping up its efforts to introduce WiMAX competitor LTE to U.S. users.

Nokia will focus on LTE (Long Term Evolution) as its preferred network and plans to launch devices for those networks in 2010, says James Harper, senior manager of technology marketing at Nokia according to GigaOm. “WiMAX has some place in the market but we do believe it’s a niche play,” says Harper.

Both WiMax and LTE are 4G technologies. WiMax is based on IEEE standards while LTE is supported by the 3GPP (3rd Generation Partnership Project) group. The biggest difference from the telecom carrier perspective between the two standards is how they will be deployed. WiMAX requires a new network to be built whereas LTE is an evolution of existing WCDMA/HSPA networks.

The upgrade to LTE makes it a more natural choice for many telecom carriers and that’s what Nokia is counting on. MetroPCS has already said it will support LTE. MetroPCS plans to launch a smartphone in the second or third quarter says Tom
Keys
, chief operating officer for the company.

That’s not good news for Clearwire. Clearwire is backed by Comcast, Intel, Time Warner Cable, Google and
Bright House Networks, which together have invested $3.2 billion in the company. Clearwire’s open all-IP network can provide users with average download speeds initially of 2-4 megabits per second and peak rates that are considerably faster, says the company.

But without enough support from device makers and other telecom carriers, Sprint which combined its 4G assets with Clearwire may find itself in the minority.

Read More http://www.wired.com/gadgetlab/2009/03/wimax-vs-lte-ba/#ixzz0kKaEbd4Q

Read More http://www.wired.com/gadgetlab/2009/03/wimax-vs-lte-ba/#ixzz0kKaEdOfH

Recent Posts

  • Multiphase 48 Volt Conversion for Low Noise Applications in an Instrument Grade Power Supply
  • Marine Obstruction Warning System
  • Mil/Aero & ASIC design services
  • RF Design with NextGen wireless LTE

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Automatic Test Equipment (ATE) Copper Strap Construction Device under test (DUT) IC Test Instrument Instrument Grade Power Supply Low Noise Applications marine warning system Multiphase 48 Volt Conversion Parasitic ringing Planar Construction Power supply output voltage Transformer construction
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