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AN247 डेटा पत्रक PDF( Datasheet डाउनलोड )


डेटा पत्रक - Reficed EMI Techniques - Philips

भाग संख्या AN247
समारोह Reficed EMI Techniques
मैन्युफैक्चरर्स Philips 
लोगो Philips लोगो 
पूर्व दर्शन
1 Page
		
<?=AN247?> डेटा पत्रक पीडीएफ

AN247 pdf
Philips Semiconductors
PCK2001 (CKBF) reduced EMI techniques
Application note
AN247
INTRODUCTION
Most PC manufactures are required to meet these EMI testing
This application note describes the background, technique and
results of EMI measurements on the PCK2001 (CKBF), showing
reduced EMI emissions over standard design techniques. Through
the use of circuit design, the high frequency EMI emissions from the
CKBF were reduced from a standard design approach. These
reduced emissions should help a board/systems manufacturer pass
FCC and CISPR EMI requirements.
requirements for system level design. Because of the
regularity/repetition of the clock signals, the clock synthesis (CK100)
and clock buffer (CKBF) in the 440BX (CK97 specification from Intel)
designs create a significant amount of noise and EMI. The CK97
specification from Intel does not require spread spectrum techniques
on the CK100 synthesis part or other reduced EMI techniques, but
only specified spread spectrum as an option. There is also no
reference to reduced EMI requirements on the CKBF. Early board
BACKGROUND OF EMI, FCC AND CISPR
STANDARDS
EMI, Electro-Magnetic Interference, is any unwanted
electromagnetic signal which may degrade the performance of an
electronic device. It is generally thought of as one device creating
electromagnetic radiation that interferes with the operation or
performance of another device. PCs and PC motherboard designs
builds and subsequent qualifications showed a serious problem with
EMI, with a strong correlation to the CK100 and CKBF parts from all
vendors. Spread spectrum on the CK100 helped, but Intel asked
that the vendors of the clock parts develop a system clock generator
(CK100) and distribution (CKBF) with 6–10 dB of radiation reduction.
Figure 1 shows a graphical interpretation of the FCC and CISPR
requirements for system level EMI performance.
have to meet standards set by regulatory agencies. Two standards
are, FCC (Federal Communications Commission) regulations part
15B, and International Electrotechnical Commission’s International
Special Committee on Radio Interference (CISPR) 22B. These
regulations specify limits:
The testing of the EMI performance of a board under FCC
regulations is done as either an open box (plastic) or a closed box
(metal/shielded) and an Open Air Test Site (OATS). The antenna for
the test is placed 3 meters away (FCC) or 10 meters away (CISPR)
in front of the system with peripherals attached, such as keyboard,
mouse, and headphones.
FCC Part 15B
Even though the test is a system level test, the main contributors to
Frequency (MHz)
Radiation (dB µV/M)
EMI are, of course, the microprocessor and the clock and data
30–88
40.0
distribution circuit. This application note will focus on the EMI results
of the Philips PCK2001 or CKBF. Methods to reduce EMI from a
88–216
43.5 board standpoint are outlined well in the Intel application note,
216–960
46.0
www.DataSheet4AU.Pco5m89, available at the Intel WEB site, www.intel.com.
Above 960
* Quasi-peak measured at 3 meters.
CISPR 22B Limits
54.0
As a vendor of clock components, Philips Semiconductors worked to
provide a CKBF (PCK2001) with a reduction in the amount of EMI
radiation by 6 dB at the 600 MHz point (our internal goal was 10 dB).
This was accomplished by designing the device to reduce the high
frequency harmonics that were being generated during switching.
Frequency (MHz)
Radiation (dB µV/M)
30–230
30.0
230–1000
37.0
* Quasi-peak measured at 10 meters.
60
50
40
dB µV 30
20
10
0
0
1998 May 18
Regulatory Limits to EMI
FCC Part 15B
CISPR 22B Limits
200 400 600 800 1000
Frequency (MHz)
Figure 1. Regulatory Limits
2
SW00280

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