Spread-Spectrum Clock Generator
Electromagnetic Interference (EMI) is a major challenge for designers of electronic devices. Strict guidelines enforced by the FCC and European Union regulate the amount of EMI a system can generate. Frequency references, whether crystal oscillators or silicon based PLLs, can be a major source of EMI on circuit boards. Spread spectrum is a technique where the output frequency is modulated slightly to lower the peak energy generated by a clock. Using spread spectrum lowers clock generated EMI from both the fundamental frequency and subsequent harmonics, thereby reducing the total system EMI.
IDT has a proprietary mix of analog and digital phase-locked loop (PLL) technologies that is the basis of an extensive portfolio of flexible spread spectrum products. IDT’s spread products support two different types of spread spectrum: down spread and center spread. Center spread modulates evenly around the clock frequency while down spread modulates below the clock frequency. The type of spread used depends on the specifications of the clock destination. Some destination chipsets, CPU’s, etc have a maximum clock frequency specification that cannot be violated. In these cases, down spread should be applied.
IDT’s spread portfolio has products supporting crystal or clock reference inputs. For systems requiring spread injection on clock reference inputs, IDT’s high performance PLL technology maintains good phase noise and high performance while reducing EMI. By using IDT’s spread spectrum technology, customers maintain high performance while saving cost and design time on expensive shielding, chokes and ferrite beads.
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| Part Number | Outputs (#) | Output Type | Output Freq Range (MHz) | Input Freq (MHz) | Inputs (#) | Input Signal | Output Banks (#) | Core Voltage (V) | Output Voltage (V) | Output Skew (ps) | Phase Noise Typ RMS (ps) | Phase Noise Max RMS (ps) | C-C Jitter Typ P-P (ps) | C-C Jitter Max P-P (ps) | Period Jitter Typ P-P (ps) | Period Jitter Max P-P (ps) | App Jitter Compliance | Prog. Clock | Prog. Interface | Reference Output | Spread Spectrum | Feedback Input |
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