Slew Rate Controlled Level Shifter Without Quiescent Current
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Solution Overview
Problem
Conventional slew rate controlled level shifters exhibit quiescent current after the output signal is held stable at a selected voltage level, reducing battery life in portable devices.
Innovation Solution
A level shifter circuit with first and second parallel current paths controlled by switch transistors and a Wilson current mirror circuit that selectively couples the output node to either a high voltage source or ground, minimizing current flow during stable voltage levels by turning off current paths after signal transitions are complete.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional slew rate controlled level shifters are used to enable communication between devices with different operating voltages, then voltage level conversion is achieved, but quiescent current flows after the output signal is held stable, reducing battery life
Solution Approach 1:
The patent applies dynamics by making the current paths dynamic rather than static. The first and second current paths are selectively enabled and disabled based on the state of the output signal. When the output signal is transitioning, the current paths are active to drive the voltage level changes. When the output signal reaches its target voltage level and becomes stable, the current paths are turned off to eliminate quiescent current. This dynamic switching of current paths resolves the contradiction between maintaining reliable voltage level conversion and reducing power consumption during stable states.
Solution Approach 2:
The patent implements periodic action through the cyclic enabling and disabling of current paths. The current paths are periodically activated during voltage transitions and deactivated during stable periods. This periodic operation pattern allows the level shifter to consume power only when necessary for voltage level conversion, while remaining in a low-power state during stable output conditions, thereby extending battery life without compromising communication reliability.
2Reliability
If current paths remain active to maintain stable output voltage levels, then reliable voltage conversion is ensured, but quiescent current continues to flow, reducing battery life
Solution Approach 1:
The patent extracts the harmful quiescent current by selectively removing (turning off) the current paths when they are no longer needed for voltage level conversion. The control circuitry monitors the output signal state and disconnects the current paths from the power supply once the output reaches its target voltage level. This extraction of unnecessary current flow eliminates the source of quiescent current while maintaining reliable voltage conversion during active periods.
Solution Approach 2:
The patent discards the continuous current flow that causes quiescent current consumption. By turning off the current paths during stable output states, the system discards the unnecessary power consumption. The current paths are then recovered and re-enabled when voltage transitions are needed, allowing the system to maintain reliability only when necessary rather than continuously consuming power.
Data Source
AI summary
A level shifter circuit includes two parallel current paths respectively controlled by switch transistors, a Wilson current mirror circuit, and a slew rate control circuit to selectively couple an output node either to a high (first) voltage source or to a ground (second voltage) source in response to differential input control signals signal. When the output node reaches a stable (high or low) voltage level, the low voltage on one of the current paths turns off a Wilson current mirror transistor in the other current path, thereby preventing quiescent current during stable periods. An optional cascode transistor is added to facilitate fabrication using low threshold voltage transistors.