Switched-Capacitor Current Source Circuit for Ripple-Stable Reference Current
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Solution Overview
Problem
Conventional current source circuits using switched-capacitor circuits face issues with voltage ripple causing errors in reference currents, leading to instability due to potential operational amplifier oscillation, which is exacerbated by increased capacitance, and reduced stability when capacitance is decreased to suppress ripple.
Innovation Solution
A current source circuit design utilizing a pair of capacitors, a switching circuit, and an operational amplifier to control charging, transferring, and discharging electric charge, along with a variable resistor and comparator to adjust resistance values, ensuring stable reference current generation without ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the capacitance in the filter circuit is increased to suppress voltage ripple, then the ripple suppression effect is improved, but the operational amplifier may oscillate and circuit stability decreases
Solution Approach 1:
The patent divides the single capacitor filter into two capacitors (first capacitor and second capacitor) connected in series. This segmentation allows the total capacitance to be distributed, reducing the risk of oscillation while maintaining ripple suppression capability. Each capacitor contributes to filtering but with reduced individual impact on amplifier stability.
Solution Approach 2:
The patent introduces a switching circuit as an intermediary between the capacitors and the operational amplifier. This switching circuit controls the charging and discharging of the capacitors, managing the interaction between the filter and amplifier to prevent oscillation while maintaining effective ripple filtering.
2Reliability
If the capacitance is reduced to prevent operational amplifier oscillation, then circuit stability is improved, but voltage ripple cannot be sufficiently suppressed
Solution Approach 1:
By segmenting the filter capacitance into two series capacitors, the patent achieves effective ripple filtering with reduced individual capacitance values. The series configuration maintains the filtering function while preventing the operational amplifier from oscillating, thus resolving the contradiction between stability and ripple suppression.
3Manufacturing precision
If a switched-capacitor circuit is used instead of a resistive element to achieve high accuracy, then manufacturing precision is improved, but voltage ripple occurs during switching operation
Solution Approach 1:
The patent introduces a filter circuit comprising two capacitors and a switching circuit as an intermediary between the switched-capacitor circuit and the operational amplifier. This intermediary filters out the voltage ripple generated during switching operations while preserving the high accuracy benefits of using capacitive elements instead of resistive elements.
Solution Approach 2:
The switching circuit performs periodic charging and discharging of the capacitors at controlled timings. This periodic action, when properly synchronized and filtered, allows the circuit to maintain high accuracy while minimizing ripple effects through the dual-capacitor filtering mechanism.
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 improves circuit stability by suppressing voltage ripple, reduces operational amplifier oscillation risk, and enhances accuracy by using capacitive elements, allowing for simplified circuit design and reduced test costs.
Implementation Method 1
a current source circuit in which a filter circuit including a capacitor and a resistor is added between the connection node and an input terminal of the operational amplifier has been proposed
Implementation Method 2
an operational amplifier amplifies a difference between a terminal voltage of the other of the pair of capacitors and a predetermined reference voltage and outputs the difference that has been amplified as an output voltage
Data Source
AI summary
To improve stability of a reference current in a current source circuit that generates the reference current by using capacitors. The current source circuit includes a pair of capacitors, a switching circuit, an operational amplifier, and an output transistor. The switching circuit charges one of the pair of capacitors with a predetermined charging current, and transfers electric charge from the one of the pair of capacitors to the other of the pair of capacitors. The operational amplifier amplifies a difference between the terminal voltage of the other of the pair of capacitors and a predetermined reference voltage and outputs the difference that has been amplified as an output voltage. The output transistor outputs a current corresponding to the output voltage as a reference current.