Bidirectional Transmission Switch With Off-State Injection Current Bypass
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Solution Overview
Problem
Existing transmission switches in multiplexers experience current or charge injection during the off state, leading to crosstalk, noise, and performance issues in connected circuits due to parasitic diodes and supply voltage changes.
Innovation Solution
A bidirectional transmission switch with an injection current control circuit that includes a detection circuit and bypass circuit, diverting injection currents to ground through parallel n-MOS and p-MOS transistors, ensuring minimal circuit area and maintaining switch stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a transmission switch is used in multiplexer, then signal transmission efficiency is improved, but current injection and charge injection occur during off state causing crosstalk and noise
Solution Approach 1:
The harmful injection current is extracted and diverted from the main signal path by introducing a separate bypass circuit connected to ground. This bypass circuit provides a dedicated path for the injection current to flow away from the output, effectively removing the harmful effect while preserving the main transmission function.
Solution Approach 2:
A bypass circuit acts as an intermediary element between the transmission switch and ground. This intermediary provides a controlled path for injection current to flow to ground through transistors that are activated only when injection current is detected, mediating between the harmful current and the sensitive output circuitry.
2Object-generated harmful factors
If bypass circuit is added to handle injection current, then crosstalk and noise are reduced, but circuit area increases
Solution Approach 1:
The bypass circuit uses the same n-MOS and p-MOS transistor types that are already present in the transmission switch, making the circuit elements universal. These transistors serve dual purposes: forming part of the transmission switch during normal operation and forming the bypass path during injection current conditions, thereby avoiding additional area overhead.
Solution Approach 2:
The bypass circuit is merged with the transmission switch by sharing common transistors and control logic. The injection current detection circuit shares control signals with the transmission switch, and the bypass transistors are integrated into the existing circuit layout, combining multiple functions into a unified structure that minimizes area.
3Difficulty of detecting and measuring
If detection circuit is implemented, then injection current can be identified, but device complexity increases
Solution Approach 1:
The detection circuit utilizes the natural voltage changes caused by injection current itself to trigger the bypass mechanism. When injection current flows, it creates a detectable voltage drop or rise that automatically activates the bypass transistors without requiring external monitoring or complex control logic, making the system self-diagnosing and self-correcting.
Solution Approach 2:
The circuit implements a feedback mechanism where the state of the transmission switch and the presence of injection current continuously influence the bypass circuit operation. The bypass circuit monitors the output node voltage and adjusts its conduction state accordingly, creating a closed-loop system that automatically responds to injection current conditions.
Data Source
AI summary
A transmission unit including a transmission switch and an injection current control circuit is provided. The transmission switch includes a plurality of n-MOS and p-MOS transistors connected to one another in parallel, and the injection current control circuit includes an injection current detection circuit that is arranged for being activated upon detection of an injection current in an output side or an input side of the transmission unit, the transmission unit further includes a bypass circuit arranged for being activated by the injection current detection circuit and further arranged for bypassing the injection current to a ground upon detection of the injection current. A multiplexer, and demultiplexer including such a transmission unit is also provided herein.