Bidirectional Transmission Switch Bypass for OFF-State Injection Current
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Solution Overview
Problem
Transmission switches in multiplexers experience current injection issues during the OFF state, leading to crosstalk and noise due to positive and negative injection currents, which can inadvertently turn on MOSFETs and affect the performance of other circuits sharing the same power supply.
Innovation Solution
A transmission unit with a parallel configuration of n-MOS and p-MOS transistors, including an injection current detection circuit and a bypass circuit that diverts injection currents to ground, ensuring minimal circuitry and maintaining the switch in the OFF state by forming a path to ground for both positive and negative injection currents without affecting the power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a transmission switch is used in multiplexer, then signal switching efficiency is improved, but current injection during OFF state causes crosstalk and noise
Solution Approach 1:
A bypass circuit is introduced as an intermediary component that provides a dedicated path for injection current to flow to ground, isolating the harmful current from the main signal path and preventing crosstalk and noise in the multiplexer output
Solution Approach 2:
The harmful injection current is extracted from the main signal path by routing it through a separate bypass circuit to ground, removing the source of crosstalk and noise while preserving the signal switching function
2Object-affected harmful factors
If bypass circuit is added to handle injection current, then crosstalk is reduced, but circuit area increases
Solution Approach 1:
The bypass circuit is merged with the existing transmission switch structure by utilizing the body diodes of the MOSFETs and adding minimal external components, combining the signal switching function with the injection current handling function in a compact integrated design
3Device complexity
If injection current is not controlled, then circuit simplicity is maintained, but on-resistance stability of other channels is affected
Solution Approach 1:
The bypass circuit provides preliminary protection by capturing and diverting injection current before it can reach the power supply and affect the on-resistance of other switched channels, preventing the stability issue before it occurs
Data Source
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AI summary
A transmission unit comprising a transmission switch and an injection current control circuit, wherein said transmission switch comprises a plurality of n-MOS and p-MOS transistors connected to one another in parallel, wherein said injection current control circuit comprises 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 said transmission unit, said transmission unit further comprising a bypass circuit arranged for being activated by said injection current detection circuit and further arranged for bypassing said injection current to a ground upon detection of said injection current. A multiplexer, and demultiplexer comprising such a transmission unit is also presented herein.