Signal Level Shifter Circuit to Prevent Crowbar Current
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Solution Overview
Problem
As device feature size decreases in CMOS integrated circuits, increased electric fields can damage junctions and oxide layers, and the difference in signal levels between circuits with varying power supply voltages leads to inefficiencies and power consumption issues, particularly when interfacing digital circuits with different voltage ranges.
Innovation Solution
A signal level shifting system comprising a first inverter with a pull-up and pull-down device, coupled with a control module that decouples and enables the pull-up device based on input signal transitions, preventing simultaneous enablement and reducing crowbar currents, thereby adjusting signal levels to match the voltage range of external circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a low voltage power supply is provided to CMOS devices to reduce power consumption and prevent damage, then power consumption and device reliability are improved, but the IC cannot interface with external circuits operating at higher voltages
Solution Approach 1:
A level shifter circuit is introduced as an intermediary component between the low-voltage internal circuits and high-voltage external circuits. The level shifter includes a first inverter operating at low voltage and a second inverter operating at high voltage, with control logic that translates signal levels and enables proper interfacing while maintaining the low-voltage operation of internal CMOS devices
2Reliability
If different power supply voltages are used for internal and external circuits, then power consumption is reduced and device reliability is improved, but signal level differences cause simultaneous enablement of pull-up and pull-down devices
Solution Approach 1:
The control module detects the voltage level of the input signal in advance and preemptively disables the pull-up device before the input signal transitions to a logic high state. This preliminary action prevents the simultaneous enablement of pull-up and pull-down devices, eliminating crowbar current and reducing power consumption
3Reliability
If the maximum voltage potential is scaled downward to prevent damage to CMOS devices, then device reliability is improved, but the IC cannot operate with external circuits at higher voltages
Solution Approach 1:
The IC is segmented into distinct voltage domains: internal circuits operate at low voltage (e.g., 1.8V) while external interface circuits operate at high voltage (e.g., 3.3V). The level shifter acts as a boundary between these domains, allowing each segment to operate at its optimal voltage level for reliability while maintaining overall system compatibility
Data Source
AI summary
A system for signal level shifting in an IC can include a first inverter having a first pull-up device and a pull-down device, wherein the first inverter is operable to receive an input signal having a voltage potential at a logic high that does not disable the first pull-up device. The system can include a second inverter coupled in series to an output of the first inverter, and a control module coupled to the output of the first inverter and an output of the second inverter. Prior to the input signal transitioning to the logic high, the control module is operable to decouple the input signal from the first pull-up device, disable the first pull-up device, and close a feedback loop that latches an output state of the second inverter.