Ring Oscillator Differential Amplifier Variable Resistance
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Solution Overview
Problem
Conventional ring oscillators in semiconductor memory devices, such as DRAM, face challenges with varying oscillation periods due to power source voltage and temperature variations, and struggle to achieve a wide resonance frequency range and low resonance voltage while minimizing jitter noise.
Innovation Solution
A ring oscillator design incorporating differential amplifiers with variable resistances controlled by the operating power source voltage, allowing for a phase difference of over 90 degrees and a wider resonance frequency range, and utilizing a feedback-generated power source voltage to reduce jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a differential amplifier type ring oscillator is used to reduce the influence of external noise, then the stability against temperature and voltage variations is improved, but the circuit complexity increases
Solution Approach 1:
The differential amplifier is divided into multiple stages (first differential amplifier stage, second differential amplifier stage) with each stage performing a specific function. This segmentation allows the circuit to achieve high stability while maintaining manageable complexity by distributing functions across stages.
Solution Approach 2:
Different parts of the circuit are given different properties: the first differential amplifier stage uses specific transistor configurations for noise rejection, while the second stage uses different configurations for signal amplification. This local optimization allows each part to excel at its specific function, achieving overall high reliability without unnecessary complexity throughout the entire circuit.
2Productivity
If the oscillation frequency of ring oscillator is increased to achieve higher performance, then the productivity is improved, but the influence from temperature, voltage, and process variations increases
Solution Approach 1:
The patent employs a phase-locked loop (PLL) configuration where the ring oscillator's output is fed back through a frequency divider and phase frequency detector to control the VCO frequency. This feedback mechanism allows the system to achieve high oscillation frequencies while automatically compensating for variations caused by temperature, voltage, and process changes, thus maintaining both high productivity and reliability.
Solution Approach 2:
The circuit uses variable resistance elements and adjustable bias currents that can be dynamically changed to optimize the oscillation frequency. By changing these parameters adaptively, the system can maintain stable operation across different frequency ranges while compensating for environmental variations, achieving both high frequency performance and reliability.
3Device complexity
If a conventional ring oscillator is used in DRAM to control refresh period, then the device complexity is kept low, but the oscillation period varies greatly with power source voltage and temperature
Solution Approach 1:
The patent implements a PLL-based frequency control system where the ring oscillator is part of a larger feedback loop. The phase frequency detector compares the oscillator output with a reference signal, and the charge pump adjusts the VCO frequency accordingly. This feedback mechanism allows the system to maintain a stable oscillation period for DRAM refresh control without significantly increasing device complexity, as the feedback components are integrated into the existing memory controller architecture.
Data Source
AI summary
A differential amplifier circuit for use in a ring oscillator includes first and second MOS transistors to each source of which an operating power source voltage is applied, and which individually respond to first and second input signals with mutually contrary phases applied to gates thereof; cross-coupled first and second-stage transistors of which each drain-source channel is connected between each drain of the first and second MOS transistors and a ground voltage level; a first variable resistance, which is connected between a drain of the first MOS transistor cross-connected to a second gate of the cross-coupled second-stage transistors, and a first gate of the cross-coupled first-stage transistors, and which is controlled by the operating power source voltage applied to a gate thereof; and a second variable resistance, which is connected between a drain of the second MOS transistor cross-connected to a second gate of the cross-coupled first-stage transistors, and a first gate of the cross-coupled second-stage transistors, and which is controlled by the operating power source voltage applied to a gate thereof. Accordingly, the ring oscillator can ensure a greater resonance frequency range as compared with the conventional oscillator, and, at the same time, jitter characteristics are improved.