Two-Stage Ring VCO With Substrate Forward Bias for 0.5 V Operation
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Solution Overview
Problem
Conventional ring oscillators face challenges in operating at ultra-low supply voltages, such as 0.5 V, due to high transistor threshold voltages, which limits their performance and stability in modern CMOS technologies.
Innovation Solution
An ultra-low voltage two-stage ring voltage-controlled oscillator is designed with a substrate forward bias structure, utilizing PMOS and NMOS transistors and a load capacitor, where the substrates of PMOS transistors are grounded or connected to a control voltage, and NMOS transistors are used for differential input ends, reducing threshold voltage and enabling efficient frequency tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional ring oscillator is used, then the oscillator can operate at normal supply voltage, but it cannot work at ultra-low voltage (0.5V) due to high transistor threshold voltage
Solution Approach 1:
The patent applies substrate forward bias technology to change the electrical parameters of the transistor by connecting the substrate to a forward bias voltage. This modifies the threshold voltage characteristic of the transistor, enabling it to operate reliably at ultra-low supply voltages (0.5V) where conventional transistors would fail due to high threshold voltage.
2Use of energy by moving object
If substrate forward bias technology is applied, then threshold voltage is reduced and supply voltage can be reduced, but device complexity increases
Solution Approach 1:
The patent integrates the substrate forward bias circuit directly into the delay unit structure of the ring oscillator. The substrate biasing is combined with the existing transistor configuration, merging the voltage reduction function into the core oscillator circuit rather than adding separate external biasing circuits, thereby reducing overall device complexity.
Solution Approach 2:
The substrate forward bias structure serves multiple functions simultaneously: it reduces the threshold voltage of the transistor, enables ultra-low voltage operation, and reduces power consumption. This multi-functional approach avoids the need for separate circuits for each function, keeping the overall device complexity manageable.
3Speed
If two-stage delay structure is used, then oscillator can work at high frequency and provide quadrature outputs, but chip area increases
Solution Approach 1:
By reducing the transistor threshold voltage through substrate forward bias, the patent enables the delay units to operate at ultra-low voltages while maintaining high-frequency performance. This parameter change allows the two-stage structure to achieve high frequency operation without requiring larger device dimensions that would increase chip area.
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
This design reduces the supply voltage, power consumption, and allows for a simple, compact circuit with a large tuning range, overcoming the limitations of conventional oscillators and enabling efficient operation at low voltages.
Implementation Method 1
Connecting a substrate of a MOS transistor to a forward bias is an effective method for reducing the threshold voltage of the transistor
Data Source
AI summary
The present utility model relates to an ultra-low voltage two-stage ring voltage-controlled oscillator applied to a chip circuit. The oscillator includes two-stage delay units. The oscillator includes two delay units that are connected end-to-end, and adjusts a working frequency by adjusting delay time of the delay unit. The delay unit includes PMOS transistors M1, M2, M3, and M4, NMOS transistors M5, M6, M7, and M8, and a load capacitor CL. The two-stage ring voltage-controlled oscillator of the present utility model uses a substrate feed forward bias structure, reduces a threshold voltage of a transistor, reduces a supply voltage, reduces power consumption, has a large tuning range, and is particularly suitable for a system that works at a low supply voltage.