Analog Switch Circuit With PMOS Isolation Against Reverse Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing analog switch circuits face challenges in preventing reverse current flow through the back gate of PMOS transistors when disconnected, which can affect voltage levels and introduce signal distortion.
Innovation Solution
The proposed analog switch circuit includes a third PMOS transistor connected between an intermediate node and the drain of an NMOS transistor, with its gate connected to the gate of the NMOS transistor, preventing reverse current flow and reducing signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a basic analog switch circuit using NMOS and PMOS transistors is used, then the switch can be turned on and off by control signals, but reverse current flows through the back gate of PMOS transistors when disconnected, causing voltage level changes and signal distortion
Solution Approach 1:
A third PMOS transistor is introduced as an intermediary component between the intermediate node and the drain of the first NMOS transistor. This intermediary transistor acts as a current blocking element that prevents reverse current from flowing through the back gates of the first and second PMOS transistors, thereby eliminating the harmful effect while maintaining the basic switch functionality.
Solution Approach 2:
The third PMOS transistor is configured to proactively prevent reverse current flow before it can affect the voltage levels and cause signal distortion. By positioning this transistor to block the reverse current path in advance, the circuit preemptively counteracts the harmful effect, ensuring stable voltage levels and signal integrity during the disconnected state.
2Reliability
If the third PMOS transistor is added to prevent reverse current, then signal distortion is reduced and voltage levels are stabilized, but the device complexity increases
Solution Approach 1:
The third PMOS transistor serves multiple functions simultaneously: it acts as a current blocking element to prevent reverse current flow, functions as a voltage stabilizer to maintain stable voltage levels at the intermediate node, and operates as a signal protection mechanism. This multi-functionality justifies the added complexity by delivering multiple benefits from a single component addition.
Data Source
AI summary
Provided is an analog switch circuit including an intermediate node, a first PMOS transistor including a source connected to the input node and a back gate and a drain connected to the intermediate node, a second PMOS transistor including a source connected to the output node, a back gate and a drain connected to the intermediate node, and a gate connected to a gate of the first PMOS transistor, a first NMOS transistor including a source grounded and a drain connected to the gates of the first PMOS transistor and the second PMOS transistor, a third PMOS transistor connected between the intermediate node and the drain of the first NMOS transistor, a first resistor connected between the gate of the first NMOS transistor and a ground, and a driver including an input that receives the control signal and an output connected to the gate of the first NMOS transistor.