RC-Based Clock Generator With PTAT Temperature Compensation
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Solution Overview
Problem
On-chip clock generators for system-on-chip integrated circuits experience significant frequency variations due to process, voltage, and temperature (PVT) variations, necessitating a solution to minimize these effects.
Innovation Solution
A clock generator incorporating a resistor-capacitor-based voltage-controlled oscillator (RC-based VCO) coupled with a temperature compensator to stabilize oscillation frequency against temperature changes, using a ring oscillator and a proportional-to-absolute-temperature (PTAT) current generator to adjust the input voltage and compensate for frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an on-chip oscillator is used to generate clock signal, then cost and size are reduced, but frequency variation increases due to PVT effects
Solution Approach 1:
The patent uses a PTAT current generator to generate a compensation voltage that changes with temperature. This compensation voltage is applied to the RC-based VCO to counteract the temperature-dependent frequency drift, thereby maintaining stable oscillation frequency across temperature variations while keeping the oscillator on-chip.
Solution Approach 2:
The patent introduces a temperature compensator as an intermediary component between the temperature environment and the RC-based VCO. The compensator generates a compensation voltage based on temperature sensing, which then adjusts the VCO's operating point to compensate for temperature-induced frequency variations.
2Reliability
If temperature compensation is added to the RC-based VCO, then frequency stability under temperature variation is improved, but device complexity increases
Solution Approach 1:
The temperature compensator exploits the inherent temperature dependence of transistor characteristics to generate a PTAT current without requiring external temperature sensors. This current is then converted to a compensation voltage that automatically tracks temperature changes, providing frequency stabilization through parameter modulation rather than complex control logic.
Solution Approach 2:
The patent merges the temperature compensation function with the existing VCO circuitry by integrating the PTAT current generator and compensation voltage source directly into the oscillator structure. This consolidation allows frequency stabilization to be achieved without adding separate, independent compensation circuits, thereby limiting the increase in overall device complexity.
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 effectively reduces the relative change in oscillation frequency with temperature changes, maintaining stability under PVT variations, thereby enhancing the reliability and accuracy of the clock signal generation.
Implementation Method 1
using a ring oscillator and a proportional-to-absolute-temperature (PTAT) current generator to adjust the input voltage and compensate for frequency variations
Implementation Method 2
a resistor-capacitor-based voltage-controlled oscillator (RC-based VCO) generates an output signal with oscillation frequency controlled by an input voltage
Data Source
AI summary
A clock generator includes a resistor-capacitor-based voltage-controlled oscillator (RC-based VCO) that generates an output signal with oscillation frequency controlled by an input voltage at an input node; and a temperature compensator that generates the input voltage to compensate change of the oscillation frequency associated with a change in temperature.