Bi-Directional Current Sensing With Virtual Voltage Noise Cancellation
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Solution Overview
Problem
Bi-directional DC-DC converters in storage devices face challenges in preventing overcurrent issues during sudden power-off situations, which can lead to data loss and incomplete operations, and existing solutions suffer from noise interference and inefficiencies in current sensing.
Innovation Solution
A bi-directional current sensor is designed to sense currents in both boost and buck modes using a voltage clamp circuit, amplifiers, a polarity selector, and a source follower, generating a virtual voltage for noise cancellation and overcurrent detection, ensuring high noise filtering performance in high voltage environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bi-directional current sensor is used to sense current in both boost and buck modes, then overcurrent prevention capability is improved, but noise filtering performance deteriorates in high voltage environments
Solution Approach 1:
The patent introduces a virtual ground node as an intermediary reference point for the differential amplifier. This virtual ground, created through the source follower transistor and resistive divider network, acts as a noise-immune reference that isolates the sensing circuit from high-voltage switching noise while still accurately reflecting the current through the second switching transistor, thereby resolving the contradiction between overcurrent detection capability and noise filtering performance
Solution Approach 2:
The patent replaces traditional voltage clamping methods with a field-effect-based approach using a source follower transistor. This transistor creates a virtual ground potential through its gate-source voltage relationship, substituting direct electrical connection with field-effect coupling. This substitution provides high-impedance isolation that naturally rejects noise while maintaining accurate current sensing through the differential amplifier
2Stability of the object's composition
If a voltage clamp circuit is used to clamp switching node voltage, then voltage stability is improved, but circuit complexity increases
Solution Approach 1:
The source follower transistor serves multiple functions simultaneously: it creates the virtual ground reference voltage, provides high-impedance buffering, establishes the reference potential for the differential amplifier, and enables noise rejection. By making this single component multi-functional, the patent achieves voltage stability without proportionally increasing circuit complexity
Solution Approach 2:
The patent embeds the virtual ground generation function within the existing current sensing circuitry. The source follower transistor and resistive divider are integrated into the feedback path of the differential amplifier, creating a nested structure where the voltage stabilization mechanism is contained within the overall sensing circuit rather than being a separate added component
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 bi-directional current sensor effectively prevents overcurrent and reduces noise interference, ensuring reliable operation and data integrity during power fluctuations by accurately sensing currents in both modes and providing robust noise cancellation.
Implementation Method 1
a voltage clamp circuit configured to clamp a switching node voltage at one end of the switching transistor to a clamp voltage
Implementation Method 2
a first amplifier configured to generate a first amplified voltage by amplifying a differential voltage between a clamp voltage and a ground voltage
Implementation Method 3
a polarity selector circuit configured to convert a polarity of the first amplified voltage into a positive voltage, based on a mode
Implementation Method 4
a second amplifier configured to amplify a differential voltage between a virtual voltage and the ground voltage and to generate a second amplified voltage
Implementation Method 5
a subtractor circuit configured to generate an amplified voltage by subtracting the second amplified voltage from the first amplified voltage
Implementation Method 6
a source follower transistor configured to transfer the amplified voltage to the virtual voltage
Implementation Method 7
a sensing transistor configured to transfer a sensing current corresponding to the virtual voltage to a ground
Data Source
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AI summary
A bi-directional direct current to direct current (DC-DC) converter includes: an inductor; a first switching transistor configured to switch a power supply voltage to one end of the inductor, in response to a first driving signal; a second switching transistor configured to switch between one end of the inductor and a ground voltage, in response to a second driving signal; and a bi-directional current sensor configured to sense a bi-directional current flowing through the second switching transistor in a boost mode and a buck mode, based on a switching node voltage at a drain of the second switching transistor, wherein the bi-directional current sensor is further configured to generate a virtual voltage of a positive voltage in a negative feedback method regardless of the sign of the switching node voltage to copy the bi-directional current.