Spread Spectrum Clock Generator With PVT-Stable Modulation Control
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Solution Overview
Problem
Existing spread spectrum clock generators (SSCGs) face challenges in maintaining a stable modulation rate due to process-voltage-temperature (PVT) variations, requiring additional components like scalars and occupying large surface areas, which affects electromagnetic interference (EMI) reduction and system operation.
Innovation Solution
A SSCG design that digitally calculates modulation rate variations using a voltage-controlled oscillator (VCO) output, adjusts the modulation charge pump current, and employs a modulation controller for precise control, eliminating the need for separate scalars and reducing filter usage, thereby maintaining a constant modulation rate and minimizing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a prior art SSCG uses a dual-loop to adjust modulation rate, then the modulation rate can be corrected for PVT variations, but the circuit occupies a large surface area due to additional filters and scalars
Solution Approach 1:
The patent extracts and removes the scalar component from the dual-loop structure, keeping only the essential feedback mechanism. This eliminates unnecessary circuit elements (scalars and additional filters) while preserving the core functionality of maintaining stable modulation rate, thereby reducing circuit surface area.
Solution Approach 2:
The feedback signal from the main divider is used for multiple purposes: it serves both as the primary PLL feedback for frequency control and as the basis for modulation rate detection. This multi-functional use of the same signal path eliminates the need for separate detection circuits and reduces overall circuit complexity and area.
2Reliability
If a prior art SSCG uses direct modulation with large charge pump size, then the modulation rate can be maintained, but the circuit complexity increases and manual adjustment is required
Solution Approach 1:
The patent implements a feedback mechanism where the modulation controller continuously monitors the actual modulation rate by comparing the feedback signal from the main divider against a target modulation rate. Based on this comparison, it dynamically adjusts the charge pump current to maintain the desired modulation rate, eliminating manual adjustment requirements and reducing circuit complexity.
Solution Approach 2:
The modulation controller automatically detects and corrects its own modulation rate deviations using the feedback signal, making the system self-regulating. This self-service capability eliminates the need for external manual adjustments and complex control circuits, simplifying the overall device structure.
3Ease of operation
If the VCO gain and charge pump size vary with PVT conditions, then the modulation rate becomes unstable, but adding correction circuits increases the circuit area
Solution Approach 1:
The patent replaces complex mechanical-style correction circuits (scalars, additional filters) with a digital-like feedback control mechanism that uses signal processing to achieve PVT invariance. The modulation controller detects frequency deviations and adjusts the charge pump accordingly, achieving robustness against PVT variations without requiring additional analog correction components that would increase circuit area.
4Measurement precision
If a scalar is used to scale the modulation voltage, then the modulation rate can be adjusted, but the precision requirement increases and circuit area expands
Solution Approach 1:
The patent removes the scalar component entirely from the circuit architecture. Instead of scaling the modulation voltage through a separate scalar circuit, the modulation controller directly regulates the charge pump current based on feedback, achieving precise modulation rate control without the area and precision constraints associated with scalars.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a PVT-invariant modulation rate, reduces circuit area, and effectively disperses energy to minimize EMI, enhancing system stability and operation without manual adjustments.
Implementation Method 1
a voltage control oscillator (VCO) generating the SSC signal based on the second control voltage signal
Implementation Method 2
a charge pump and filter unit outputting a first control voltage signal in response to the detector output signal
Data Source
AI summary
A spread spectrum clock generator (SSCG) and method of generating a spread spectrum clock (SSC) signal, in which the SSCG may include a controller outputting a given modulation voltage signal based on a difference between an average frequency of a first feedback signal and a comparison frequency signal input thereto, or based on comparison in total phase variations between a second feedback signal and the comparison frequency signal, and a sub-system for generating a first control voltage as a function of an input reference frequency signal and a second feedback signal input thereto. An adder may add the first control voltage signal and the modulation voltage signal to generate a second control voltage signal, and a voltage control oscillator (VCO) may generate the SSC signal based on the second control voltage signal.