Fast Level Shifter Circuit With Weak-PFET Contention Control
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Solution Overview
Problem
Conventional level shifters suffer from transition delay and excessive power consumption due to shoot-through currents and contention between PFETs and NFETs during signal transitions, which are exacerbated at higher supply voltages.
Innovation Solution
The proposed level shifter circuit incorporates a specific configuration of NFETs and PFETs, including weak PFETs and NFETs with aspect ratios optimized for reduced contention and power consumption, where the gates and drains of PFETs and NFETs are strategically coupled to prevent shoot-through currents and minimize propagation delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional level shifter configuration with cross-coupled PFETs and NFETs is used, then signal transfer between voltage domains is achieved, but shoot-through currents occur during transition phases causing excessive power consumption
Solution Approach 1:
A weak PFET is introduced as an intermediary device between the cross-coupled PFETs and NFETs. This weak PFET acts as a mediator that controls the interaction between the strong PFETs and NFETs during transition phases, allowing the strong devices to be turned off completely to eliminate shoot-through currents, while still enabling signal transfer through the weak PFET's controlled conduction.
Solution Approach 2:
The patent applies different device strengths (qualities) to different positions in the circuit. The weak PFET is specifically designed with lower drive strength and placed in the critical path where it controls the transition, while the strong cross-coupled PFETs and NFETs are positioned for signal amplification. This local differentiation of device qualities enables precise control of current flow to eliminate shoot-through while maintaining signal transfer capability.
2Speed
If cross-coupled PFETs and NFETs are used for level shifting, then voltage domain translation is achieved, but transition delay increases due to contention between devices
Solution Approach 1:
The weak PFET serves as an intermediary that mediates the transition process between input and output. By controlling the weak PFET's gate voltage, the circuit can smoothly transition the state without direct contention between the strong cross-coupled devices, thereby reducing transition delay while achieving complete device turn-off for low power consumption.
Solution Approach 2:
The weak PFET is used to preliminarily prepare the transition state before the strong cross-coupled devices fully switch. By gradually modulating the weak PFET's conduction, the circuit pre-charges or pre-discharges relevant nodes, reducing the abrupt switching stress and minimizing propagation delay caused by device contention.
Data Source
AI summary
A lever shifter is provided for receiving a signal in a first voltage domain and providing an output signal in a second voltage domain. The level shifter reduces propagation delay and power consumption by mitigating contention between NFETs and PFETs during signal propagation.