Capacitor-Coupled Level Shifter for Duty Cycle Balance
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Solution Overview
Problem
Level shifters face issues with time delay and duty cycle errors due to differences in pull-up voltages, causing uneven signal transitions and potential errors in signal processing, particularly when handling clock signals.
Innovation Solution
A level shifter design incorporating serially coupled inverters with capacitors between output nodes to stabilize signal transitions by equalizing voltage levels and reducing time delays, ensuring balanced rising and falling edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If different pull-up voltages are used in serially coupled inverters, then voltage level shifting is achieved, but time delay and duty cycle errors occur due to uneven signal transitions
Solution Approach 1:
A capacitor is introduced as an intermediary element between the output nodes of two inverters with different pull-up voltages. The capacitor couples the output nodes, enabling voltage level shifting while the capacitor's charge transfer mechanism equalizes the signal transitions and minimizes duty cycle errors, thus maintaining signal integrity across different voltage domains
Solution Approach 2:
The invention changes the electrical parameters by introducing a capacitor that dynamically adjusts the voltage transfer characteristics. The capacitor's charging and discharging cycles modify the effective pull-up voltage seen by the second inverter, balancing the rising and falling edge times despite the difference in nominal pull-up voltages between the two inverters
2Adaptability or versatility
If pull-up voltage differences exist between inverters, then voltage level conversion is enabled, but rising and falling edges become unbalanced causing duty cycle errors
Solution Approach 1:
The capacitor serves as a mediating element that transfers charge between the output nodes of inverters operating at different voltage levels. This charge transfer mechanism compensates for the asymmetry in rising and falling edges caused by different pull-up voltages, thereby preserving duty cycle accuracy during voltage level conversion
Solution Approach 2:
The capacitor equalizes the potential difference between the two output nodes during signal transitions. By charging and discharging in response to voltage changes, the capacitor creates a balancing effect that temporarily equalizes the voltage conditions at both nodes, ensuring symmetric rising and falling edges despite different nominal voltage levels
Data Source
AI summary
A level shifter includes: a first inverter suitable for inverting a signal of a first node based on a first pull-up voltage and a first pull-down voltage; a second inverter suitable for inverting the signal of the first node based on a second pull-up voltage and a second pull-down voltage; and a capacitor coupled between an output node of the first inverter and an output node of the second inverter.