Output Driver Assist Circuit for Faster Signal Transitions
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Solution Overview
Problem
Existing output circuits for semiconductor integrated circuit devices face challenges in achieving high-speed operation with low power consumption while maintaining a compact circuit area, as variations in power source voltages can decrease the driving capability of transistors, leading to increased signal delay.
Innovation Solution
The proposed output circuit incorporates a p-type output transistor with a drive assist circuit that temporarily raises the gate-source voltage by bringing down the potential at the output node when the gate signal transitions from high to low, enhancing the driving capability and transition speed without increasing transistor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the p-type transistor size is increased to complement driving capability, then the delay of output signal is reduced, but the circuit area is increased
Solution Approach 1:
The drive assist circuit performs preliminary action by temporarily bringing down the potential at the power source end before the gate signal transitions, which enhances the gate-source voltage and driving capability of the p-type transistor during the critical transition period, thereby reducing output signal delay without requiring transistor size increase
Solution Approach 2:
The invention changes the voltage parameter dynamically by temporarily adjusting the potential at the power source end through the drive assist circuit, creating a time-varying gate-source voltage that enhances transistor driving capability only when needed for signal transitions, thus avoiding the need for permanently larger transistor dimensions
2Loss of time
If the gate-source voltage is increased to enhance driving capability, then the delay of output signal is reduced, but the power consumption is increased
Solution Approach 1:
The drive assist circuit implements periodic action by temporarily activating only during signal transitions when enhanced driving capability is needed, rather than continuously operating, thus reducing overall power consumption while still achieving fast signal transitions when required
Solution Approach 2:
The circuit performs preliminary action by pre-charging or pre-discharging the output node through the drive assist circuit before the main switching event, which reduces the burden on the main transistor during switching, allowing for lower continuous power consumption while maintaining fast transition speeds
Data Source
AI summary
An output transistor (2) has a source connected to a VDD1 and a drain connected to an output terminal (1). A pre-driver (3) receives a signal varying in accordance with a data input signal (DIN), and provides a gate signal (SG1) to a gate of the output transistor (2), the gate signal (SG1) transiting between the VDD1 and a potential (VP) at a power source end (4). When a VDD2 is output from an output node (N1) and an assist signal (SA) makes a first transition corresponding to the transition of the gate signal (SG1) from HIGH to LOW, the drive assist circuit (20) performs an assist operation in which a potential of the output node (N1) is temporarily brought down from VDD2.