Spread Spectrum Clock Generator Digital Modulator EMI
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Solution Overview
Problem
Existing spread spectrum clock generators are inefficient in uniformly spreading electromagnetic interference (EMI) over a desired range, leading to higher EMI at lower frequencies and increased circuit complexity, cost, and power consumption.
Innovation Solution
A spread spectrum clock generator using a digital modulator and a single relaxation oscillator, which varies the frequency of the clock signal by altering the number of cycles in each state to ensure uniform EMI spreading without requiring additional oscillators or complex phase locked loops, implemented with a digital modulator and a divider to achieve efficient EMI reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a triangular wave signal is used to vary the clock frequency, then the frequency spectrum is spread uniformly over the desired range, but the EMI spreading becomes less than perfect when implemented using practical circuits and requires expensive circuit area and cost
Solution Approach 1:
The patent replaces the traditional analog triangular wave modulation mechanism with a digital frequency hopping spread spectrum technique. Instead of using a continuous analog triangular wave to modulate the clock frequency, the system uses a digital state machine to generate pseudorandom frequency hops across a set of discrete frequency channels. This substitution of digital for analog mechanics achieves uniform EMI spreading while reducing circuit complexity and cost.
Solution Approach 2:
The patent changes the fundamental parameter of frequency modulation from continuous analog variation (triangular wave) to discrete digital frequency hopping. The system transitions between predetermined frequency channels based on pseudorandom sequences generated by a state machine, thereby achieving spectrum spreading through parameter changes in the frequency domain while simplifying the implementation circuitry.
2Object-affected harmful factors
If multiple oscillators or complex phase locked loops are used to achieve uniform EMI spreading, then the EMI reduction is improved, but the circuit complexity and power consumption increase
Solution Approach 1:
The patent merges the functions of multiple oscillators and phase-locked loops into a single oscillator system controlled by a digital frequency hop controller. Instead of requiring separate oscillators for different frequency channels, the system uses one oscillator whose frequency is dynamically switched between predetermined channels based on pseudorandom sequences, thereby achieving the same EMI spreading effect with reduced complexity.
Solution Approach 2:
The system employs a self-contained digital state machine that generates its own pseudorandom frequency hopping sequences without requiring external complex control circuits. The state machine autonomously manages the frequency transitions and coordination, eliminating the need for complex external phase-locked loop circuits and reducing overall system complexity while maintaining effective EMI spreading.
3Object-affected harmful factors
If traditional spread spectrum techniques are implemented, then EMI is reduced, but the circuit area and power consumption increase
Solution Approach 1:
The patent employs simple digital logic elements and a basic relaxation oscillator instead of expensive, power-hungry analog modulation circuits. The frequency hopping is achieved through straightforward digital state machine control that switches between predetermined frequency channels, using minimal power compared to continuous analog triangular wave generation and processing required by traditional spread spectrum techniques.
Data Source
AI summary
In one form, a spread spectrum clock generator includes an oscillator and a digital modulator. The oscillator has a control input for setting an output frequency, and an output for providing a clock output signal. The digital modulator is responsive to the clock output signal to provide a control code to the control input of the oscillator as a periodic signal with a plurality of discrete steps, wherein the digital modulator provides said control code at each of said plurality of discrete steps for substantially a predetermined time.