Electronic Components Datasheet Search
  English  ▼
ALLDATASHEET.NET

X  

SM561 Datasheet(PDF) 5 Page - Cypress Semiconductor

Part # SM561
Description  Spread Spectrum Clock Generator
Download  8 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Manufacturer  CYPRESS [Cypress Semiconductor]
Direct Link  http://www.cypress.com
Logo CYPRESS - Cypress Semiconductor

SM561 Datasheet(HTML) 5 Page - Cypress Semiconductor

  SM561 Datasheet HTML 1Page - Cypress Semiconductor SM561 Datasheet HTML 2Page - Cypress Semiconductor SM561 Datasheet HTML 3Page - Cypress Semiconductor SM561 Datasheet HTML 4Page - Cypress Semiconductor SM561 Datasheet HTML 5Page - Cypress Semiconductor SM561 Datasheet HTML 6Page - Cypress Semiconductor SM561 Datasheet HTML 7Page - Cypress Semiconductor SM561 Datasheet HTML 8Page - Cypress Semiconductor  
Zoom Inzoom in Zoom Outzoom out
 5 / 8 page
background image
SM561
Document #: 38-07021 Rev. *C
Page 5 of 8
SSCG Theory of Operation
The SM561 is a PLL-type clock generator using a proprietary
Cypress design. By precisely controlling the bandwidth of the
output clock, the SM561 becomes a Low EMI clock generator.
The theory and detailed operation of the SM561 will be
discussed in the following sections.
EMI
All digital clocks generate unwanted energy in their harmonics.
Conventional digital clocks are square waves with a duty cycle
that is very close to 50%. Because of this 50/50 duty cycle,
digital clocks generate most of their harmonic energy in the
odd harmonics, i.e., third, fifth, seventh, etc. It is possible to
reduce the amount of energy contained in the fundamental
and odd harmonics by increasing the bandwidth of the funda-
mental clock frequency. Conventional digital clocks have a
very high Q factor, which means that all of the energy at that
frequency is concentrated in a very narrow bandwidth, conse-
quently, higher energy peaks. Regulatory agencies test
electronic equipment by the amount of peak energy radiated
from the equipment. By reducing the peak energy at the funda-
mental and harmonic frequencies, the equipment under test is
able to satisfy agency requirements for EMI. Conventional
methods of reducing EMI have been to use shielding, filtering,
multilayer PCBs, etc. The SM561 uses the approach of
reducing the peak energy in the clock by increasing the clock
bandwidth, and lowering the Q.
SSCG
SSCG uses a patented technology of modulating the clock
over a very narrow bandwidth and controlled rate of change,
both peak and cycle to cycle. The SM561 takes a narrow band
digital reference clock in the range of 54–166 MHz and
produces a clock that sweeps between a controlled start and
stop frequency and precise rate of change. To understand
what happens to a clock when SSCG is applied, consider a
65-MHz clock with a 50% duty cycle. From a 65-MHz clock we
know the following, as illustrated here.
If this clock is applied to the Xin/CLK pin of the SM561, the
output clock at pin 4 (SSCLK) will be sweeping back and forth
between two frequencies. These two frequencies, F1 and F2,
are used to calculate to total amount of spread or bandwidth
applied to the reference clock at pin 1. As the clock is making
the transition from F1 to F2, the amount of time and sweep
waveform play a very important role in the amount of EMI
reduction realized from an SSCG clock.
The modulation domain analyzer is used to visualize the
sweep waveform and sweep period. Figure 1 also shows the
modulation profile of a 65-MHz SSCG clock. Notice that the
actual sweep waveform is not a simple sine or sawtooth
waveform. Figure 2 is a scan of the same SSCG clock using
a spectrum analyzer. In this scan you can see a 6.48-dB
reduction in the peak RF energy when using the SSCG clock.
Modulation Rate
Spectrum
Spread
Clock
Generators
utilize
frequency
modulation (FM) to distribute energy over a specific band of
frequencies. The maximum frequency of the clock (Fmax) and
minimum frequency of the clock (Fmin) determine this band of
frequencies. The time required to transition from Fmin to Fmax
and back to Fmin is the period of the Modulation Rate, Tmr.
Modulation Rates of SSCG clocks are generally referred to in
terms of frequency or Fmod = 1/Tmod.
The input clock frequency, Fin, and the internal divider count,
Cdiv, determine the Modulation Rate. In some SSCG clock
generators, the selected range determines the internal divider
count. In other SSCG clocks, the internal divider count is fixed
over the operating range of the part. The SM560 and SM561
have a fixed divider count, as listed below.
Tc = 15.4 ns
50 %
50 %
Clock Frequency = fc = 65 MHz
Clock Period = Tc =1/65 MHz = 15.4 ns


Similar Part No. - SM561

ManufacturerPart #DatasheetDescription
logo
Bourns Electronic Solut...
SM561-1 BOURNS-SM561-1 Datasheet
183Kb / 1P
   ADSL Line Transformers
logo
Datatronic Distribution...
SM561-1 DATATRONICS-SM561-1 Datasheet
102Kb / 1P
   ADSL Line Transformers
logo
Bourns Electronic Solut...
SM561-1E BOURNS-SM561-1E Datasheet
183Kb / 1P
   ADSL Line Transformers
logo
Nippon Precision Circui...
SM5610 NPC-SM5610 Datasheet
150Kb / 6P
   IC for Quartz Crystal Oscillating Module
logo
List of Unclassifed Man...
SM5611 ETC2-SM5611 Datasheet
337Kb / 2P
   OEM PRESSURE TRANSDUCER FULLY TEMPERATURE COMPENSATED AND CALIBRATED DUAL-IN-LINE PACKAGE
More results

Similar Description - SM561

ManufacturerPart #DatasheetDescription
logo
Fujitsu Component Limit...
MB88151A FUJITSU-MB88151A Datasheet
342Kb / 22P
   Spread Spectrum Clock Generator
logo
Cypress Semiconductor
CY25811 CYPRESS-CY25811 Datasheet
316Kb / 11P
   Spread Spectrum Clock Generator
logo
Fujitsu Component Limit...
MB88156 FUJITSU-MB88156 Datasheet
198Kb / 25P
   Spread Spectrum Clock Generator
logo
ON Semiconductor
PCS3P25811 ONSEMI-PCS3P25811 Datasheet
159Kb / 9P
   Spread Spectrum Clock Generator
JANUARY 2010 ??Rev. 1
logo
Fujitsu Component Limit...
MB88162 FUJITSU-MB88162 Datasheet
170Kb / 21P
   Spread Spectrum Clock Generator
MB88R157 FUJITSU-MB88R157 Datasheet
139Kb / 24P
   Spread Spectrum Clock Generator
logo
PulseCore Semiconductor
PCS3P2191A PULSECORE-PCS3P2191A Datasheet
358Kb / 8P
   Spread Spectrum Clock Generator
logo
Integrated Device Techn...
IDT5V50009 IDT-IDT5V50009 Datasheet
181Kb / 8P
   SPREAD SPECTRUM CLOCK GENERATOR
logo
Cypress Semiconductor
MB88151A CYPRESS-MB88151A Datasheet
568Kb / 27P
   Spread Spectrum Clock Generator
CY25566 CYPRESS-CY25566 Datasheet
116Kb / 9P
   Spread Spectrum Clock Generator
More results


Html Pages

1 2 3 4 5 6 7 8


Datasheet Download

Go To PDF Page


Link URL




Privacy Policy
ALLDATASHEET.NET
Does ALLDATASHEET help your business so far?  [ DONATE ] 

About Alldatasheet   |   Advertisement   |   Contact us   |   Privacy Policy   |   Link Exchange   |   Manufacturer List
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com