Output Driver Pre-Driver Shaping for Low-Noise MOSFET Switching
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Solution Overview
Problem
Existing output driver circuits for integrated circuits face challenges in controlling noise and power consumption due to increased through current, which leads to waveform quality deterioration and higher power consumption, especially when trying to suppress noise through current di/dt.
Innovation Solution
A driver device with a first and second pre-driver unit that controls the driver transistors to round the signal waveform near the threshold and sharply change it beyond the threshold, delaying the turn-on of one transistor with respect to the other to reduce noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the waveforms of the signal net_p and the signal net_n are rounded to suppress noise (through current di/dt), then noise is reduced, but the time period during which the p-MOSFET 101-1 and the n-MOSFET 101-2 are simultaneously on is increased, causing large through current to flow between power supply voltage VDD and ground potential VSS
Solution Approach 1:
The pre-driver circuits 102-1 and 102-2 perform preliminary waveform shaping on the control signals net_p and net_n before they reach the driver transistors. By rounding the waveforms in advance, the switching timing is optimized to minimize the overlap period when both transistors are simultaneously conductive, thereby reducing through current and power consumption while maintaining noise suppression benefits
2Object-affected harmful factors
If the waveforms of the signal net_p and the signal net_n are rounded, then noise (through current di/dt) is suppressed, but the quality of the waveform of the output signal 104 deteriorates, causing reduction in signal level, timing error, increase in jitter, and retardation of rise and fall
Solution Approach 1:
The waveform rounding is applied selectively and locally to specific portions of the control signals. The pre-driver circuits 102-1 and 102-2 shape the waveforms to have rounded edges during critical switching transitions to suppress noise, while maintaining sharp edges in other portions to preserve signal integrity and waveform quality at the output
Solution Approach 2:
The pre-driver circuits dynamically adjust the waveform characteristics of net_p and net_n based on the switching state. The rounding is applied adaptively to minimize noise during transitions while preserving the ability to maintain stable high and low levels, thereby balancing noise suppression with waveform quality preservation
3Object-affected harmful factors
If the waveforms of the signal net_p and the signal net_n are rounded, then noise is suppressed, but the rise and fall times of the output signal 104 are retarded
Solution Approach 1:
The pre-driver circuits perform preliminary waveform shaping that prepares the control signals for optimal switching. By pre-rounding the waveforms with controlled characteristics, the actual switching transitions occur more efficiently, achieving noise suppression without significant retardation of rise and fall times in the final output signal
4Object-affected harmful factors
If the waveforms of the signal net_p and the signal net_n are rounded, then noise is suppressed, but noise tolerance during state transition is reduced
Solution Approach 1:
The waveform rounding is applied locally and selectively to specific transition regions of the control signals, rather than uniformly across the entire waveform. This localized approach suppresses noise during transitions while preserving the sharpness and stability of logic levels, thereby maintaining noise tolerance during state transitions
Data Source
AI summary
A driver device drives a load circuit by a common output signal from a first driver transistor and a second driver transistor. The driver device includes a first pre-driver unit that outputs a first driver control signal to the first driver transistor in response to the input signal; and a second pre-driver unit that outputs a second driver control signal to the second driver transistor in response to the input signal. The first pre-driver unit controls the first driver control signal in such a manner that the first driver control signal is rounded in the vicinity of a threshold of the first driver transistor and is sharply changed in a region exceeding the threshold.