Voltage Boost Circuit for eDRAM Using Thin Oxide FETs
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Solution Overview
Problem
Conventional voltage boost circuits using charge pumps often exceed the oxide-stress limit of field effect transistors (FETs), leading to reliability issues and poor performance due to the need for thick oxide FETs, which are low performance and costly in terms of chip space and power consumption.
Innovation Solution
A voltage boost circuit utilizing a boost capacitor and a drive capacitor to precharge a thin oxide FET, allowing a boosted supply voltage to be passed through the FET while limiting gate-to-source oxide stress by controlling the gate voltage to be within the reliability limits, using a precharge phase and a pump phase to generate a boosted output voltage without overstressing the FET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick oxide FETs are used to exceed the oxide-stress limit, then reliability is improved, but device performance deteriorates
Solution Approach 1:
The gate capacitor is precharged to a high voltage (VPP) before the pump phase begins. This preliminary action ensures that when the thin oxide FET turns on, the gate already has the necessary voltage to sustain high-frequency operation without immediately stressing the oxide beyond its limit. The precharge phase prepares the electrical conditions in advance, allowing the thin oxide device to operate reliably at high performance.
Solution Approach 2:
The circuit operates in periodic phases: a precharge phase where the gate capacitor is charged to VPP, followed by a pump phase where the thin oxide FET operates at high performance. This periodic switching between phases allows the thin oxide FET to experience high-performance intervals without continuous oxide stress, resolving the contradiction between reliability and performance.
2Reliability
If thick oxide FETs are used to ensure reliability, then oxide stress is reduced, but chip space and power consumption increase
Solution Approach 1:
The invention changes the voltage parameter dynamically by precharging the gate capacitor to a high voltage (VPP) before the pump phase. This parameter change allows the thin oxide FET to operate with reduced oxide stress during critical high-performance intervals, eliminating the need for thick oxide devices that would otherwise be required to ensure reliability under continuous high voltage stress.
3Power
If voltage boost is implemented using charge pumps, then higher voltage is generated, but oxide stress limit is exceeded
Solution Approach 1:
The gate capacitor serves as an intermediary energy storage element between the voltage boost circuit and the thin oxide FET. It is precharged to the high voltage (VPP) required for boosting, then discharged through the FET gate during the pump phase. This intermediary approach allows the thin oxide FET to experience the necessary high voltage for boosting without being continuously stressed beyond its oxide limit, as the capacitor mediates the voltage delivery in controlled phases.
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
Enables the generation of a boosted output voltage approximately twice the supply voltage using thin oxide FETs, maintaining reliability and performance without the need for thick oxide FETs, thus reducing power consumption and chip space requirements.
Implementation Method 1
a boost capacitor which is precharged with a precharge voltage in a precharge stage and which provides a boosted supply voltage to a thin oxide FET during a pump phase
Implementation Method 2
a drive capacitor which provides a turn on voltage to the thin oxide FET so that the boosted supply voltage can pass to an output node
Data Source
AI summary
A voltage boost circuit for eDram using thin oxide field effect transistors (FETs) is disclosed. The voltage boost circuit includes a boost capacitor which is precharged with a precharge voltage in a precharge stage and which provides a boosted supply voltage to a thin oxide FET during a pump phase. The voltage boost circuit further include a drive capacitor which provides a turn on voltage to the thin oxide FET so that the boosted supply voltage can pass to an output node in the pump phase.