Negative Bootstrap Level Shifter for GaN Half-Bridge Signal Transfer
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Solution Overview
Problem
High-voltage half-bridge switching circuits face challenges in efficiently transferring control signals across different voltage domains, particularly when the floating supply voltage is lower than the system ground, leading to issues with noise immunity and correct signal transfer, especially when using GaN transistors.
Innovation Solution
A negative bootstrap circuit is implemented using capacitors and buffers to shift the ground reference of the level shifter, allowing for the correct transfer of control signals by generating a negative voltage across the capacitors, which are coupled to the ground reference in a selectable manner through a selection circuit commanded by digital pulses, ensuring reliable operation even when the floating supply is equal or lower than the system ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional level shifter is used to transfer control signals across voltage domains, then signal transfer is possible, but noise immunity deteriorates when the floating supply voltage is lower than the system ground
Solution Approach 1:
The patent inverts the conventional approach by generating a negative voltage at the ground reference node instead of using a positive voltage bootstrap. This negative voltage is generated using a pump capacitor that is selectively coupled to the ground reference through a selection circuit commanded by digital pulses, creating a voltage domain shift that maintains noise immunity even when the floating supply is below ground potential
Solution Approach 2:
The patent changes the voltage parameter of the ground reference from conventional positive/zero voltage to negative voltage. By dynamically adjusting the ground reference voltage to negative levels using the pump capacitor and selection circuit, the circuit maintains proper signal transfer reliability while improving noise immunity in conditions where the floating supply voltage is lower than the system ground
2Adaptability or versatility
If the floating supply voltage is allowed to go below system ground to enable wider operating range, then adaptability improves, but signal transfer correctness deteriorates
Solution Approach 1:
The patent introduces a negative voltage ground reference as an intermediary between the floating supply and the control signal. This negative voltage acts as a mediator that allows the floating supply to operate below system ground while maintaining correct signal transfer by providing a sufficient voltage headroom for the level shifter to function properly
Solution Approach 2:
By dynamically changing the ground reference voltage parameter to negative values using the pump capacitor, the circuit expands its adaptability to accommodate floating supply voltages below system ground while maintaining signal transfer correctness through the adjusted voltage relationship
3Device complexity
If a positive voltage bootstrap is used to maintain ground reference, then circuit simplicity is maintained, but operation fails when floating supply is below ground
Solution Approach 1:
The patent inverts the conventional positive voltage bootstrap approach by implementing a negative voltage bootstrap. Instead of generating positive voltage above ground, the pump capacitor generates negative voltage below ground, enabling operation when the floating supply is below ground while maintaining a relatively simple circuit structure
Solution Approach 2:
The patent employs periodic action through the selection circuit that is commanded by digital pulses to selectively couple the pump capacitor to the ground reference. This periodic switching enables the negative voltage generation only when needed, maintaining circuit simplicity while achieving the required adaptability for operation under negative differential voltage conditions
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 solution enhances noise immunity and ensures correct signal transfer across voltage domains, maintaining system operation even when the floating supply voltage is below a certain threshold, reducing circuit complexity and power consumption compared to alternative solutions.
Implementation Method 1
A negative bootstrap circuit is implemented using capacitors and buffers to shift the ground reference of the level shifter, allowing for the correct transfer of control signals by generating a negative voltage across the capacitors
Data Source
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AI summary
A circuit (21, 22) to transfer a command signal (CS) in a circuit (20) comprising circuit stages which are voltage supplied by different voltage domains (VCC, GND; FS, FG) including a first voltage domain (VCC, GND) comprising first voltage levels represented by a first voltage supply (VCC) and a first voltage reference (GND), in particular a DC voltage supply and a DC ground, and a second voltage domain (FS, FG) comprising second voltage levels represented by a second voltage supply (VFS) and a second voltage reference (VFG), in particular a floating supply and a floating ground, and said circuit (21, 22) to transfer a signal (CS) operating according to the first voltage domain (VCC, GND) to a stage (HS_DRV, PW1) operating according to the second voltage domain (FS, FG), said circuit (21, 22) to transfer a command signal (CS) including a logic component (224) operating according to the second voltage domain (FS, FG) logically driving said stage (HS_DRV, PW1), and a level shifting circuit (22; 32; 42) coupled to the second voltage supply (FS) and to the first ground reference (GND), said level shifting circuit (22; 32; 42) including two paths coupled between said second voltage supply (FS) and to the first ground reference (GND), each including a high voltage transistor (221a, 221b) coupled through a respective resistor (223a, 223b) to the second voltage supply (FS) and through a respective commanded current generator (222a; 222b) to the first ground reference (GND), each path being coupled to a respective input (S,R) of the logic component (224), said commanded current generator (222a; 222b) being commanded by pulse signals (Tp1, Tp2) generated by a pulse generator (225) on the basis of said command signal (CS), characterized in that said level shifting circuit (32; 42) includes a negative bootstrap circuit (C1, INV1, INV2, C2, INV3, INV4; Cpump, SINV, FINV, 228, 229) including at least a pump capacitor (C1, C2; Cpump) arranged between the current generators (222a; 222b) and the first ground reference (GND) and configured to shift at a negative voltage said first ground reference (GND) synchronically with the activation of the respective commanded current generator (222a; 222b).