Cascode Output Driver for 1.8V/3.3V Interface Reliability
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Solution Overview
Problem
Conventional output driving circuits for semiconductor devices face reliability issues when operating with high voltage interfaces, particularly when transitioning between 1.8 V and 3.3 V, due to the decreased thickness of the oxide layer in current process technologies, making it difficult to maintain reliable gate-source, gate-drain, and drain-source voltage conditions.
Innovation Solution
The proposed output driving circuit incorporates a three-stage cascode structure with NMOS transistors and PMOS transistors in a sequential configuration, including an internal resistor and an inverter, to manage voltage levels and feedback signals effectively, ensuring the reliability of the semiconductor device across a wider voltage range by maintaining the voltage difference within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If CMOSFETs with medium gate oxide for 1.8V operation or thin gate oxide for 0.9V operation are used to achieve high-speed operation and low supply voltage, then operation speed and energy efficiency are improved, but the circuit cannot work properly when 3.3V is applied, reducing voltage compatibility
Solution Approach 1:
The output driving circuit is divided into multiple stages: a first output stage with transistors configured for high-voltage operation (3.3V) and a second output stage with transistors configured for low-voltage operation (1.8V or 0.9V). This segmentation allows each stage to operate within its optimal voltage range, enabling the circuit to support both high-voltage and low-voltage interfaces while maintaining high-speed performance.
2Manufacturing precision
If the oxide layer thickness is decreased to enable higher integration and lower supply voltage operation, then manufacturing precision and integration density are improved, but the reliability of gate-source, gate-drain, and drain-source voltage conditions deteriorates under high voltage
Solution Approach 1:
Different transistor types are used in different parts of the circuit: PMOS transistors with thicker oxide layers are used in the first output stage that handles high-voltage signals (3.3V), while NMOS transistors with thinner oxide layers are used in the second output stage for low-voltage operation. This local differentiation of transistor characteristics allows the circuit to maintain reliability under high-voltage conditions while achieving high integration density through thin oxide technology.
Data Source
AI summary
The output driving circuit include a pull-down driver, an input/output (IO) control logic, a gate control logic, and an inverter. The pull-down driver includes first, second, and third transistors that are sequentially coupled between a pad and a ground node. The IO control logic is configured to receive a clock signal and an enable signal, and transfer a first control signal to the third transistor. The gate control logic is configured to receive a voltage of the pad and output a feedback voltage to a gate electrode of the first transistor. The inverter is configured to invert the enable signal and transfer an inverted enable signal to the gate control logic. Therefore, the reliability of the output driving circuit can be improved.