Digital Current Source Using Segmented Mirror Cells
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Solution Overview
Problem
Current generator circuits, such as those used in MRAM applications, face issues with uncontrolled and unpredictable variations in output current due to design limitations in both simple current mirror and feedback amplifier-based systems, leading to inefficiencies and performance issues.
Innovation Solution
A digital current source utilizing one bit precision current mirror cells with feedback amplifiers and switching components, controlled by a digital control word, to precisely mirror a reference current, ensuring accurate and controlled output current across multiple bit precision current mirror cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple current mirror circuit is used, then the circuit complexity is reduced, but the output current precision deteriorates due to uncontrolled variations
Solution Approach 1:
The current mirror circuit is divided into multiple independent one-bit current mirror cells, each handling a specific bit of the digital control word. This segmentation allows precise control of each current component while maintaining manageable circuit complexity through modular design.
Solution Approach 2:
The circuit transitions from a static current mirror to a dynamic digitally controlled system where the output current can be precisely adjusted in real-time based on the digital control word, enabling adaptive current control while maintaining precision.
2Measurement precision
If a feedback amplifier is used, then the output current precision is improved, but the power consumption increases due to continuous operation
Solution Approach 1:
The feedback amplifier operates periodically rather than continuously - it is activated only during calibration phases to establish precise reference voltages, then powered down during normal operation. This periodic operation maintains precision while dramatically reducing average power consumption.
Solution Approach 2:
The feedback amplifier performs preliminary calibration actions to establish accurate reference voltages and current levels before normal operation begins. This preliminary precision setup enables subsequent operation with lower power consumption while maintaining the established precision.
3Device complexity
If the reference voltage is placed outside the feedback loop, then the circuit complexity is reduced, but the output current precision deteriorates due to uncontrolled variations
Solution Approach 1:
The reference voltage is placed inside the feedback loop, allowing the feedback amplifier to continuously monitor and adjust the reference voltage to compensate for variations. This feedback mechanism ensures precise output current control while the modular one-bit cell design keeps overall circuit complexity manageable.
4Adaptability or versatility
If digital control is implemented for current mirroring, then the adaptability is improved, but the device complexity increases due to additional control circuitry
Solution Approach 1:
The digital control system is segmented into multiple one-bit control cells, each corresponding to a specific bit of the control word. This segmentation provides full digital control adaptability while keeping each control cell simple and modular, preventing overall complexity from becoming unmanageable.
Data Source
AI summary
A digital current source used to mirror a reference current is provided. The digitally controlled analog current source multiplies a current from a master mirror transistor producing an output current that is a digitally controlled multiple of the reference current. The circuit comprises a plurality of one bit current mirror cells. Each one bit current mirror cell comprises a mirror transistor receiving an analog gate voltage from a master mirror transistor and providing a drain voltage, an operational amplifier configured to maintain the drain voltage for the mirror transistor equivalent to the analog gate voltage, and a switch configured to receive one control bit, the switch enabling current mirroring when the mirror voltage is substantially equivalent to the master mirror voltage. The digital current source further includes a common line summing element employed to receive and compile currents from each of the one bit current mirror cells.