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NPC develops new spread spectrum clock generators (SSCG) that effectively reduces EMI and jitter
Nippon Precision Circuits, Inc. (NPC, Main office: 4-3 Fukuzumi 2-chome, Koto-Ku, Tokyo, President: Yoshifumi Gomi) has developed two spread spectrum clock generators (SSCG)*1, "SM876x series", that can effectively lower EMI*2 (unwanted radiation) of electronic components, making the best use of its crystal oscillation and high-performance device technologies in timing fields such as PLL*3 application.
As the speed and density of electronic systems have increased, the frequency of the clock used in these systems also has increased. Consequently, EMI noise emitted from the systems tends to increase. This EMI noise affects the systems by causing malfunctioning or degradation of the performance and is strictly regulated by various standards. To satisfy these standards, various actions have been conventionally taken, such as electromagnetic shield, ferrite beads, and choke coil. Recently, however, SSCG that can reduce the number of components responsible for EMI has increasingly been used to help create compact electronic components and systems at low cost.
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SM8760CA
SM8761AA
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Against this background, NPC has developed spread spectrum clock generator LSIs, the SM876x series, by making the best use of its crystal oscillation IC and clock generator LSI production technologies.
SSCG is a technology to reduce the maximum peak of the unwanted radiation spectrum in the output frequency by slightly fluctuating the oscillation frequency of PLL. With conventional SSCG, a peak of spectrum was created at the poles of the modulation cycle of the oscillation frequency (maximum modulation point and minimum modulation point), degrading the effect of reducing the EMI noise. The SM876x series has suppressed the peak of spectrum and realized a high effect of lowering EMI, by employing an original modulation method developed by NPC. The products in this series also have low jitter output (Cycle-to-Cycle jitter*4: 250ps typ.), using the NPC's technology cultivated from developing low-jitter clock generator LSIs that were developed for DVD and DSC.
NPC plans to develop more products with different multiplication factors, spectrum modulation, and number of output pins for the SM876x series.
| *1: |
PLL: Phase Locked Loop. An electronic circuit that matches the frequencies of the input signal or reference frequency and the output signal |
| *2: |
EMI: Electromagnetic Interference |
| *3: |
SSCG: Spread Spectrum Clock Generator |
| *4: |
Cycle-to-Cycle jitter: Important evaluation parameter of PLL that defines a cycle difference T = (T2 - T1) calculated from two continuous cycle data T1 and T2. |
Overview of New Products
| Product Name |
Shipment of Sample |
Sample Price (including tax) |
Mass Production |
Mass Production Plans |
| SM8760Cx |
June 2004 |
¥400 per unit (¥420 per unit) |
July 2004 |
100,000 units per month |
| SM8761AA |
August 2004 |
October 2004 |
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 Main Features of New Product |
<SM8760Cx> |
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Spectrum modulation mode
Center spread: ±1.0% |
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Supply voltage: 3.3±0.3V |
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Operating temperature: -20 to +80°C |
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Operating current consumption: 9mA (typ.) @51MHz |
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Input frequency
With crystal oscillator connected: 12.75MHz (fundamental wave)
With external signal input: 12.75MHz |
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Multiplication factor: x4 |
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Cycle-to-Cycle jitter: 250ps (typ.) |
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Package: 8-pin VSOP |
<SM8761AA> |
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Spectrum modulation mode
Down spread: -1.0% to -3.8% |
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Supply voltage: 3.3±0.3V |
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Operating temperature: 0 to +70°C |
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Operating current consumption: 9mA (typ.) @25MHz |
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Input frequency
With crystal oscillator connected: 20MHz to 40MHz
With external signal input: 20MHz to 108MHz |
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Output frequency: 20MHz to 108MHz |
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Multiplication factor: x1 |
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Cycle-to-Cycle jitter: 250ps (typ.) |
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Package: 8-pin SOP |
Note: The above specifications are subject to change for improvements without notice. |
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SM8760CAV clock output spectrum diagram |
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· Tested IC |
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SM8760CAV |
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· Conditions |
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Supply voltage: 3.3V
Load capacitance: 15pF
Input frequency: 12.75MHz
Output frequency: 51.00MHz
Temperature: Room temperature
Tested with NPC's evaluation board |
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· Measuring instruments |
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Spectrum analyzer: MS2621A, Anritsu, Inc.
Active probe: P6201, Tektronix, Inc. |
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For more information,
Sales Group
TEL +81-3-3642-6663 FAX +81-3-3642-6698 sales@npc.co.jp
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