Feedback Level Shifter With Charge Injection for Fast Startup
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Solution Overview
Problem
Existing level shifters face challenges in minimizing power dissipation, optimizing propagation delays, and providing failsafe start-up conditions, especially in automotive applications with large voltage differences, as they often result in high quiescent currents and limited speed due to large voltage swings.
Innovation Solution
The proposed IC incorporates a level shifter with a storing element, an input stage, and a feedback loop that controls the input stage based on transitions of the storing element's output, minimizing quiescent currents and optimizing switching speed, while also including a charge injecting stage to compensate for parasitic capacitance issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a resistor based level shifter is used, then the level shifting function is achieved, but large quiescent current flows through the resistor
Solution Approach 1:
The patent employs periodic switching action through transistors Q2 and Q3 that alternately connect the resistor R1 to ground, creating pulsed current flow rather than continuous quiescent current. This periodic action reduces average power dissipation while maintaining the level shifting function through controlled charging and discharging cycles of the capacitor C1.
Solution Approach 2:
The circuit uses the capacitor C1 to store energy and maintain the output voltage level between switching events, allowing the circuit to serve itself during transitions. The capacitor discharges through the transistor switches when needed, eliminating the need for continuous resistor current flow and reducing quiescent current consumption.
2Speed
If a small value resistor is used, then quick turn-off is achieved, but large quiescent current flows
Solution Approach 1:
The patent implements periodic switching through transistors Q2 and Q3 that connect the resistor to ground only during specific phases of operation. This creates pulsed current flow that achieves fast turn-off during switching events while minimizing average quiescent current, as the resistor is not continuously connected to the high voltage domain.
Solution Approach 2:
The circuit dynamically controls the resistance value by using transistor switches to connect or disconnect the resistor R1 from the high voltage domain. During turn-off events, the transistor provides a low resistance path for quick discharge, while during normal operation, the resistor is disconnected to minimize quiescent current, achieving both speed and energy efficiency.
3Ease of operation
If large voltage swing is used in the level shifter, then level shifting between high and low voltage domains is achieved, but propagation delay increases
Solution Approach 1:
The capacitor C1 is pre-charged to the high voltage level VBOOT through the resistor R1 during the charging phase. This preliminary action ensures that when the transistor Q3 switches on, the capacitor can quickly discharge to ground, achieving fast propagation delay for the high-to-low transition while maintaining the required voltage swing for proper level shifting between domains.
Solution Approach 2:
The capacitor C1 acts as an intermediary energy storage element that facilitates rapid voltage transitions. By storing energy at the high voltage level and quickly releasing it through the transistor switches, the capacitor mediates the voltage domain conversion process, enabling fast propagation delay while achieving the necessary large voltage swing for reliable level shifting.
Data Source
AI summary
An apparatus is provided that uses a first level shifter for performing a voltage shift of a low level input signal of a first voltage domain to a high level output signal of a second voltage domain. The first level shifter comprises a storing element in the second voltage domain, an input stage coupled to the storing element for providing a signal state to be stored in the storing element and a feedback loop from an output of the storing element to the input stage for controlling the input stage in response to a transition of a high level output signal of the storing element.