Auto-Range Current Mirror Circuit for OLED Driving Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current mirror circuits using MOSFETs face accuracy issues due to unstable threshold voltage (Vth) when operating with low bias currents, leading to increased errors in output current, particularly in high-accuracy applications like OLED driving circuits where multiple small driving currents are required.
Innovation Solution
A multi-stage current mirror circuit with a current sensing circuit that adjusts the amplifying rate of front and rear stage current mirrors based on input current thresholds, using voltage converters and comparators to generate a controlling signal for MOS transistor switches, ensuring constant output current quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed amplifying rate is used in the current mirror circuit, then the circuit structure is simple, but the output current accuracy deteriorates when operating with low bias currents
Solution Approach 1:
The patent implements dynamic switching between different amplifying rates (first amplifying rate and second amplifying rate) based on the input current magnitude. The current mirror circuit transitions from a static fixed amplifying rate to a dynamic adjustable amplifying rate, selecting the appropriate amplifying rate according to whether the input current is above or below a threshold value, thereby resolving the contradiction between circuit simplicity and output current accuracy.
Solution Approach 2:
The patent changes the amplifying rate parameter of the current mirror circuit based on the input current level. By switching between different amplifying rates (e.g., 10:1 or 1:10) according to the input current magnitude, the circuit optimizes output current accuracy for different operating conditions while maintaining reasonable circuit complexity through controlled parameter variation.
2Adaptability or versatility
If a multi-stage current mirror with fixed amplifying rates is used, then the output current range is limited, but the circuit complexity increases
Solution Approach 1:
The patent makes the current mirror circuit universal by enabling it to operate effectively across a broader current range through dynamic amplifying rate switching. The same circuit structure can adapt to different input current magnitudes (above or below threshold) by switching amplifying rates, eliminating the need for multiple dedicated circuits for different current ranges and thus expanding versatility without proportionally increasing complexity.
3Ease of operation
If a single amplifying rate is used, then the circuit is easy to control, but the error of output current increases when bias current varies
Solution Approach 1:
The patent introduces a feedback mechanism where the input current magnitude is monitored and used to control the switching between different amplifying rates. The control circuit detects whether the input current is above or below a threshold and automatically selects the appropriate amplifying rate, creating a closed-loop control system that maintains output current stability across varying bias conditions while preserving ease of operation through automatic control.
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 solution significantly reduces output current errors and improves accuracy by dynamically adjusting amplifying rates, allowing for a broader range of output currents and reduced skew, especially in OLED driving circuits, enhancing the circuit's operational range and reducing production costs.
Implementation Method 1
The voltage converter has an input terminal and an output terminal. The input current is supplied to the input terminal of the voltage converter and the voltage converter converts the input current to a corresponding input voltage
Implementation Method 2
The voltage comparator has two inputs and one output. One of the inputs is connected to the output terminal of the voltage converter and another input is connected to a reference voltage. The voltage comparator compares the input voltage and reference voltage to determine an output voltage
Data Source
AI summary
An auto-range current mirror circuit has a current sensing circuit, a front and rear stage current mirrors each has an adjustable amplifying rate. The current sensing circuit presets a threshold current and has an input current of the front stage current mirror. The current sensing current compares the input current with a threshold current and then outputs a controlling signal to the front and rear stage current mirrors to adjust a suitable amplifying rate. Therefore, a bias current of the rear stage current mirror is amplified by the suitable amplifying rate to improve the quality of output current of the rear stage current mirror.