Output Buffer Bulk Switching for High-Voltage Tri-State Operation
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Solution Overview
Problem
Conventional output buffers in semiconductor devices cannot operate as tri-state buffers when an external high voltage greater than the operational voltage is applied, as the PN junction in the transistors prevents the drain voltage from being lifted to the high voltage, limiting their functionality.
Innovation Solution
Incorporating a switch circuit connected to the bulk of an output transistor that supplies the operational voltage during active mode and lifts the bulk voltage to match the external high voltage during tri-state mode, ensuring the output transistor is completely turned off to handle high voltage inputs without affecting normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output buffer uses a conventional fixed bulk voltage connection to the operational voltage, then the transistor operates reliably in active mode, but the drain voltage cannot be lifted to external high voltages greater than the operational voltage due to the turned-on PN junction
Solution Approach 1:
The bulk voltage connection is changed from a fixed state to a dynamic state controlled by the enable signal. When in tri-state mode, the bulk voltage is lifted to match the external high voltage, completely turning off the output transistor. When in active mode, the bulk voltage returns to the operational voltage for normal operation. This dynamic adjustment resolves the contradiction between reliable active mode operation and high voltage sustainability.
Solution Approach 2:
The bulk voltage parameter is changed from a fixed operational voltage to a variable voltage that can reach external high voltages. By controlling the bulk voltage to match the external high voltage in tri-state mode, the PN junction is kept reverse-biased, preventing it from turning on and allowing the drain voltage to be lifted to high voltages greater than the operational voltage.
2Adaptability or versatility
If the bulk voltage is lifted to external high voltage to enable tri-state mode with high voltage input, then the output transistor is completely turned off for high voltage sustainability, but normal active mode operation is affected
Solution Approach 1:
The bulk voltage is dynamically adjusted based on the operational mode. In tri-state mode, the bulk voltage is lifted to the external high voltage to completely turn off the transistor for high voltage sustainability. In active mode, the bulk voltage returns to the operational voltage to ensure reliable transistor operation. The enable signal controls this dynamic switching between states.
Solution Approach 2:
The bulk voltage is prepared and lifted to the external high voltage in advance before the high voltage input is applied, ensuring the transistor is completely turned off and preventing any potential damage or malfunction. This preliminary action maintains high voltage sustainability without affecting active mode operation.
3Adaptability or versatility
If the PN junction in the output transistor is allowed to turn on to accommodate high voltage input, then the drain voltage can reach high voltage levels, but the transistor cannot maintain proper tri-state operation
Solution Approach 1:
The bulk voltage parameter is changed from a fixed operational voltage to a variable voltage that can reach external high voltages. By controlling the bulk voltage to match the external high voltage, the PN junction is kept reverse-biased and does not turn on, allowing the drain voltage to be lifted to high voltage levels while maintaining proper tri-state operation.
Solution Approach 2:
The bulk voltage acts as an intermediary between the operational voltage and the external high voltage. By adjusting the bulk voltage to match the external high voltage in tri-state mode, it mediates the voltage difference and prevents the PN junction from turning on, enabling both high voltage input handling and proper tri-state functionality.
Data Source
AI summary
An output buffer includes a first output transistor, a first switch, a second switch and a third switch. The first output transistor is connected to a first operational voltage for outputting the first operational voltage as the data signal. The first switch is connected to a bulk of the first output transistor for receiving an enable signal. The second switch is connected to the first switch and a second operational voltage for receiving the enable signal, wherein the second operational voltage is lower than the first operational voltage. The third switch includes a first terminal connected to the bulk of the first output transistor, a control terminal connected to the first switch, and a second terminal connected to the first operational voltage.