Wave-Shaped Pre-Driver Timing to Reduce Crowbar Current
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Solution Overview
Problem
Digital integrated circuits face challenges in optimizing pre-driver control to minimize crowbar current and derivative of current with time (di/dt), which affects signal processing and voltage changes at power supply nodes, despite previous improvements using NAND and NOR circuitry.
Innovation Solution
The introduction of wave shaping circuitry between the conventional pre-driver and output driver, which includes specific transistor configurations and connections to delay the turn-on and turn-off times of P-channel and N-channel MOS transistors, reducing the time interval during which both transistors are conducting and thereby decreasing crowbar current and di/dt.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the rise time and fall time of the signal are decreased to improve switching speed, then the maximum frequency and signal processing speed are improved, but the derivative of current with time (di/dt) increases causing voltage changes at power supply nodes
Solution Approach 1:
The patent introduces wave shaping circuitry as an intermediary component between the pre-driver and the output driver stage. This intermediary circuit actively shapes the drive signals to the P-channel and N-channel MOS transistors, controlling their turn-on and turn-off timing to reduce di/dt while maintaining fast switching. The wave shaping circuitry acts as a mediator that reconciles the conflicting requirements of fast switching and low di/dt.
2Power
If both P-channel and N-channel MOS transistors are turned on simultaneously to improve signal amplification, then the output drive capability is improved, but crowbar current flows causing voltage changes at power supply nodes
Solution Approach 1:
The wave shaping circuitry performs preliminary action by pre-controlling the turn-on and turn-off timing of the P-channel and N-channel MOS transistors. Before the transistors can simultaneously conduct and create crowbar current, the circuit has already shaped the drive signals to ensure proper sequencing. This preliminary signal conditioning prevents the harmful simultaneous conduction while maintaining the necessary output drive capability.
3Object-generated harmful factors
If NAND and NOR circuitry is used to asymmetrically shape the drive signals to reduce crowbar current, then the simultaneous conduction time is reduced, but the circuit complexity increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the timing parameters of the drive signals to the output transistors. The wave shaping circuitry modifies the rise time, fall time, and relative timing of the P-channel and N-channel drive signals as controllable parameters. By changing these timing parameters, the circuit reduces crowbar current while avoiding the need for complex asymmetric logic circuits.
Data Source
AI summary
Disclosed is a wave shaping apparatus and a method for shaping an input pulse train signal alternating between a low level and a high level to provide a signal delaying a turn on of one output transistor with respect to a turn off of the other output transistor thus decreasing time, when both the transistors would be simultaneously conducting current.