Relaxation Oscillator Using Constant-Current Capacitor Switching
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Solution Overview
Problem
Conventional relaxation oscillators require high-speed and high-precision comparators that consume large currents and have unstable operations near the trigger point due to reduced charging currents.
Innovation Solution
A relaxation oscillator design utilizing transistors and capacitors with constant current flow, where a flip-flop's state changes based on capacitor voltages, stabilizing the operation and reducing current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a comparator is used to detect the charging voltage of the capacitor, then the on/off timing can be determined, but high-speed and high-precision comparators consume large currents and require large-scale circuits
Solution Approach 1:
The patent extracts the comparison function from a separate comparator component and integrates it into the transistor switching mechanism itself. The transistor's threshold voltage inherently provides the comparison reference, eliminating the need for an external high-precision comparator and thereby reducing current consumption and circuit scale while maintaining detection precision.
Solution Approach 2:
The transistor serves multiple functions: it acts as both the switching element and the comparison element. By making the transistor perform both switching and voltage comparison functions, the patent eliminates the need for a dedicated comparator, thus reducing overall current consumption and circuit complexity while achieving the required detection precision.
2Measurement precision
If a comparator is used to detect the charging voltage of the capacitor, then the on/off timing can be determined, but the charging current becomes smaller in the vicinity of a trigger point, making the operation unstable
Solution Approach 1:
The patent removes the vulnerable comparator component that causes instability near the trigger point. By using the transistor's inherent threshold voltage for comparison, the system avoids the comparator's reduced gain and instability issues that occur when charging current becomes small near the trigger point, thereby improving operation reliability.
Solution Approach 2:
The transistor uses its own threshold voltage characteristic to perform the comparison function, making the system self-sufficient and eliminating dependence on external comparators. This self-service approach ensures stable operation even when charging current varies near the trigger point, as the transistor's threshold voltage remains constant and reliable.
3Speed
If conventional charging methods are used, then the capacitor can be charged, but the slope of the voltage becomes non-constant near the trigger point, causing unstable operation
Solution Approach 1:
The patent preliminarily establishes a constant current charging path using a dedicated current source transistor configured to maintain constant current flow. This preliminary setup ensures that the capacitor charges with a constant voltage slope from the beginning, preventing the instability that would otherwise occur near the trigger point where conventional charging methods produce non-constant slopes.
Solution Approach 2:
The patent changes the charging parameter from variable current (conventional method) to constant current (controlled by current source transistor). This parameter change ensures that the voltage slope remains constant throughout the charging process, including near the trigger point, thereby maintaining operation stability while achieving reliable detection.
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 design achieves stable oscillations with constant voltage slope near the trigger point, low current consumption, and resistance to noise, suitable for miniaturization and high-speed operations.
Implementation Method 1
a first transistor, through which a constant current is made to flow; a first capacitor, which is charged by a current from the first transistor; a third transistor, through which a constant current is made to flow; a second capacitor, which is charged by a current from the third transistor
Data Source
AI summary
[Problem to be solved] The disclosure is to stably output a signal of a predetermined frequency.[Solution] The disclosure includes: a first transistor M1, through which a constant current is made to flow; a first capacitor C1, which is charged by a current from the first transistor M1; a second transistor M2, which draws a charge of the first capacitor C1; a third transistor M3, through which a constant current is made to flow; a second capacitor C2, which is charged by a current from the third transistor M3; a fourth transistor M4, which draws a stored charge of the second capacitor C2; and a flip-flop FF, whose state changes from a first state to a second state when a charging voltage of the first capacitor C1 reaches a predetermined value, and changes from the second state to the first state when a charging voltage of the second capacitor C2 reaches a predetermined value, the flip-flop FF causing the second transistor M2 to be turned off and the fourth transistor M4 to be turned on in the first state, and causing the second transistor M2 to be turned on and the fourth transistor M4 to be turned off in the second state; and the disclosure outputs a signal of a predetermined frequency from the flip-flop FF.