Current-Mirror Timer Circuit for Supply-Independent Oscillation
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Solution Overview
Problem
In timer circuits used in semiconductor integrated circuits, the oscillation frequency increases when the power supply voltage decreases, due to the use of an inverter as a voltage comparator, which affects the accuracy of time measurement.
Innovation Solution
A timer circuit design that includes a capacitor, a first current source, an inverter, a second current source, a current mirror circuit, and a resistor, where the current mirror circuit and resistor configuration ensures that the capacitor voltage at the threshold point is constant and independent of the power supply voltage, thereby stabilizing the oscillation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If an inverter is employed as a voltage comparator to reduce circuit scale and power consumption, then area and power consumption are reduced, but the oscillation frequency becomes dependent on power supply voltage
Solution Approach 1:
A current mirror circuit is introduced as an intermediary component between the inverter and the capacitor. The current mirror circuit receives current from the inverter and provides a compensated current to the capacitor, effectively decoupling the capacitor charging process from direct dependence on inverter threshold voltage variations. This intermediary structure allows the system to maintain low power consumption while achieving frequency stability.
Solution Approach 2:
The invention changes the control parameter from voltage-based (inverter threshold voltage) to current-based (current mirror output current). By using the current mirror circuit to replicate and compensate current, the system transforms the dependency relationship: instead of frequency being directly controlled by voltage threshold variations, it is now controlled by compensated current variations, achieving parameter independence from power supply voltage fluctuations.
2Area of stationary object
If an inverter is employed as a voltage comparator, then circuit scale is reduced, but the threshold voltage changes with power supply voltage
Solution Approach 1:
The current mirror circuit serves as a mediator that decouples the threshold voltage from the capacitor charging process. It receives the inverter's output current and provides a stabilized current to the capacitor, preventing direct transmission of threshold voltage variations to the timing function.
Solution Approach 2:
The circuit is segmented into distinct functional blocks: the inverter for voltage inversion, the current mirror circuit for current compensation, and the capacitor for timing. This segmentation allows each component to perform its specialized function independently, with the current mirror circuit specifically handling the threshold voltage stabilization task.
3Use of energy by stationary object
If the power supply voltage decreases, then power consumption is reduced, but the oscillation frequency increases
Solution Approach 1:
The current mirror circuit provides a feedback mechanism where the current from the inverter is replicated and used to compensate the capacitor charging current. This feedback loop automatically adjusts the charging current based on the inverter's output, counteracting the frequency increase that would normally occur with decreased power supply voltage.
Solution Approach 2:
The system changes from voltage-controlled timing to current-controlled timing. The current mirror circuit converts voltage variations into compensated current variations, ensuring that the capacitor charging current remains stable even when power supply voltage changes, thereby maintaining constant oscillation frequency.
Data Source
AI summary
A first current source charges a capacitor. A second current source supplies a current to an input node of an inverter. A current mirror circuit has its output node coupled to an input node of the inverter. A resistor is coupled between the input node of the current mirror circuit and the capacitor.