All-Digital Spread Spectrum Clock Generator for EMI Reduction
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Solution Overview
Problem
Conventional analog and digital spread spectrum clock generators face challenges in reducing Electromagnetic Interference (EMI), occupying large chip areas, consuming high power, and being unstable due to process, voltage, and temperature variations, while also being complex in design and difficult to apply in low-voltage systems.
Innovation Solution
An all-digital spread spectrum clock generating circuit that applies triangular modulation directly to a digital controlled oscillator, using a phase frequency detecting unit and delta-sigma modulator to control the output clock signal, maintaining central frequency stability under PVT variations and enhancing EMI reduction with a simplified circuit design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional analog spread-spectrum clock generator is used to reduce EMI, then EMI reduction is achieved, but chip area is occupied and power consumption is high
Solution Approach 1:
The patent replaces the conventional analog spread-spectrum clock generator with an all-digital implementation. The digital controlled oscillator and digital modulation circuitry eliminate the need for large on-chip capacitors and analog loop filters, achieving EMI reduction while minimizing chip area occupation.
Solution Approach 2:
The patent changes the operating parameters by using digital control signals instead of analog voltage control. The modulation index and spreading spectrum parameters are controlled through digital signals, enabling EMI reduction without requiring large capacitive elements that would increase chip area.
2Object-affected harmful factors
If conventional analog spread-spectrum clock generator is used to reduce EMI, then EMI reduction is achieved, but power consumption is high
Solution Approach 1:
The patent substitutes analog circuitry with digital circuitry, where digital controlled oscillators and logic circuits consume significantly less power than their analog counterparts. The removal of large on-chip capacitors and analog filtering components directly reduces power consumption while maintaining EMI reduction effectiveness.
3Object-affected harmful factors
If conventional spread-spectrum clock generator is used, then EMI reduction is attempted, but stability under PVT variations is poor
Solution Approach 1:
The patent replaces analog components with digital components that are inherently more stable under PVT variations. Digital controlled oscillators and digital logic circuits exhibit better process, voltage, and temperature stability compared to analog circuitry, ensuring reliable EMI reduction across varying operating conditions.
Solution Approach 2:
The patent incorporates feedback mechanisms through phase-frequency detectors and digital control loops that continuously monitor and adjust the output frequency. This feedback ensures stable operation under PVT variations while maintaining the spread-spectrum EMI reduction effect.
4Measurement precision
If phase-locked loop is used to control oscillator during triangular modulation, then frequency tracking is achieved, but triangular modulation is interfered and sine modulation is generated
Solution Approach 1:
The patent segments the frequency control function from the modulation function. The phase-frequency detector handles frequency tracking separately, while the digital controlled oscillator applies triangular modulation independently. This segmentation prevents the interference that occurs when a single PLO control loop attempts to do both, preserving the triangular modulation waveform accuracy.
Solution Approach 2:
The patent introduces digital control signals as an intermediary between the phase-frequency detector and the oscillator. These digital control signals mediate the frequency tracking requirement while allowing the triangular modulation to proceed undisturbed, preventing the degradation to sine modulation that occurs in conventional analog implementations.
Data Source
AI summary
An all-digital spread spectrum clock generating circuit with EMI reduction effect and a method for controlling the same utilize a digital spread-spectrum clock controlling unit to control a digital controlled oscillator, so that it can directly modulates an output clock frequency. Accordingly, the spectrum of the output clock frequency is spread, and the EMI effect due to the output clock signal is reduced. A spread-spectrum clock controller receives a reference clock counting signal and a dividing clock counting signal generated by a frequency detecting unit. After detecting and judging, the spread-spectrum clock controlling unit modulates and maintains a central frequency of the spread-spectrum clock periodically according to the two counting signals, thereby keeping a stability of the central frequency of the spread-spectrum clock signal and decreasing the complexity of the circuit design.