Voltage Level Down-Shifter With Pull-Down Capacitor for SOA Compliance
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Solution Overview
Problem
Existing voltage level down-shifters in integrated circuits face issues of low voltage transistors operating outside their safe operating areas (SOAs), leading to undesirable trade-offs in circuit complexity, power consumption, and area, despite design modifications like using asymmetric high voltage transistors or static bias circuits.
Innovation Solution
A voltage level shifting circuit structure incorporating an input stage with series-connected transistors and a pull-down capacitor, ensuring all transistors operate within their SOAs by using low voltage transistors and an inverter connected to an intermediate node, with a capacitor to manage voltage transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If low voltage transistors are used in voltage level down-shifters, then power consumption is reduced, but transistors operate outside their safe operating areas (SOAs)
Solution Approach 1:
The patent applies preliminary action by pre-charging the intermediate node to a high voltage level before the switching operation. This is achieved through a pull-up transistor that charges the intermediate node to VDD1 before the low voltage transistor switches. This preliminary voltage establishment ensures that when the low voltage transistor operates, the voltage differential across it remains within safe operating limits, preventing SOA violations while maintaining low power consumption characteristics
Solution Approach 2:
The patent introduces an intermediate node as a mediator between the high voltage input and low voltage output stages. This intermediate node, controlled by both high voltage and low voltage transistors, acts as a buffer that isolates the low voltage transistor from direct exposure to high voltage stress. The intermediate node's voltage is carefully managed through coordinated switching of high and low voltage transistors, ensuring the low voltage transistor never experiences voltage conditions outside its SOA
2Reliability
If asymmetric high voltage transistors are used to avoid SOA violations, then transistor reliability is improved, but circuit complexity increases
Solution Approach 1:
The patent segments the voltage level shifting function into distinct high voltage and low voltage transistor stages, each operating within their respective safe voltage ranges. The high voltage transistor handles the input voltage level, the intermediate node manages the transition, and the low voltage transistor handles the output. This segmentation allows each transistor to be optimized for its specific voltage range without requiring asymmetric high voltage transistors, thereby reducing circuit complexity while maintaining reliability
3Reliability
If static bias circuits are used to prevent SOA violations, then transistor reliability is improved, but power consumption and area increase
Solution Approach 1:
The patent employs periodic action through dynamic switching of bias conditions. Instead of using static bias circuits that continuously consume power, the circuit uses periodically activated transistors that establish appropriate voltage conditions only when needed for switching operations. The pull-up and pull-down transistors are activated in sequence to prepare and reset the intermediate node voltage, providing necessary bias conditions transiently rather than continuously, thus avoiding the continuous power consumption associated with static bias circuits
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution maintains all transistors within their safe operating areas, reducing power consumption and circuit complexity while effectively shifting voltage levels without SOA violations.
Implementation Method 1
the input stage can include a capacitor, which is connected to the input node and to the intermediate node
Data Source
AI summary
A voltage level shifter includes an input stage with series-connected first and second N-type field effect transistors (NFETs) and an output stage with an inverter connected to an intermediate node between the first and second NFETs. Gates of the first and second NFETs are connected to an output node of the inverter and an input node, respectively. An input voltage signal on the input node toggles between a first voltage and ground. An intermediate voltage signal on the intermediate node toggles between a second voltage (lower than the first voltage) and ground. An output voltage signal on the output node toggles between the second voltage and ground. A capacitor in the input stage is connected between the input and intermediate nodes so that, when the input voltage switches to ground, the intermediate voltage signal is pulled to ground to facilitate switching of the output voltage signal to the second voltage.