Low-Power Self-Adjusting Reference Current for Floating Supply Stages
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Solution Overview
Problem
Current integrated circuits face limitations in accurately controlling current references due to fabrication and temperature variations, with Band-Gap based solutions being costly and requiring large charge pumps, and existing methods struggling to transfer reference currents effectively between voltage domains.
Innovation Solution
A system comprising a first simple current reference and an accurate current reference, generating a digital error signal to adjust the current from a low-power source, using a circuit with N-channel depletion type MOS transistors and a Band-Gap based biasing circuit to provide a more accurate current reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Band-Gap based biasing circuit is used for better current reference accuracy, then the accuracy of the reference current is improved, but the current consumption increases and requires a large charge pump
Solution Approach 1:
The patent performs current reference calibration during an initial setup phase before normal operation. A high-precision Band-Gap circuit generates calibration data that is stored in lookup tables, allowing the simple current reference to be adjusted without requiring the Band-Gap circuit to operate continuously during normal low-power mode.
Solution Approach 2:
The patent divides the current reference system into two separate circuits: a simple current reference for normal low-power operation and a Band-Gap based accurate current reference for calibration only. This segmentation allows each circuit to be optimized for its specific function without compromising the other.
2Measurement precision
If a Band-Gap based biasing circuit is used for better current reference accuracy, then the accuracy of the reference current is improved, but the chip area increases due to large charge pump requirements
Solution Approach 1:
The patent performs current reference calibration during an initial setup phase before normal operation. A high-precision Band-Gap circuit generates calibration data that is stored in lookup tables, allowing the simple current reference to be adjusted without requiring the Band-Gap circuit to operate continuously during low-power mode.
Solution Approach 2:
The patent divides the current reference system into two separate circuits: a simple current reference for normal low-power operation and a Band-Gap based accurate current reference for calibration only. This segmentation allows each circuit to be optimized for its specific function without compromising the other.
3Device complexity
If a simple current reference using saturation region transistor is used, then the circuit simplicity and small area are improved, but the accuracy of the reference current deteriorates due to fabrication and temperature spread
Solution Approach 1:
The patent implements a calibration mechanism where the simple current reference is adjusted based on feedback from comparing its output against a known accurate reference. The difference (error signal) is used to modify the simple reference's parameters, effectively closing the accuracy loop without requiring the simple reference to be inherently precise.
Solution Approach 2:
The patent performs current reference calibration during an initial setup phase before normal operation. A high-precision Band-Gap circuit generates calibration data that is stored in lookup tables, allowing the simple current reference to be adjusted without requiring the Band-Gap circuit to operate continuously during low-power mode.
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
This approach allows for precise current trimming, reducing power consumption and chip real estate usage, while avoiding the need for large charge pumps and parasitic capacitances, enhancing performance in fast switching applications and electromagnetic immunity.
Implementation Method 1
For better accuracy a Band-Gap (BG) based biasing circuit may be used
Implementation Method 2
These current references can be realized, for example, by biasing a transistor in a saturation region
Data Source
AI summary
A system and method for providing an accurate current reference using a low-power current source is disclosed. A preferred embodiment comprises a system comprises a first section and a second section. The first section comprises a first simple current reference, an accurate current reference, and a circuit that generates a digital error signal based upon a comparison of an output of the first simple current reference and an output of the accurate current reference. The second section comprises a second simple current reference providing a second reference current, an adjustment circuit providing an adjustment current based upon the digital error signal, and a circuit biased with current equivalent to a summation of the second reference current and the adjustment current. The first simple current reference and the second simple current reference may be equivalent circuits.