Switch Array Interface Circuit Using Static Currents for RF Immunity
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Solution Overview
Problem
High-frequency emissions and RF interference from keyboard interfaces can disrupt sensitive RF and analogue inputs in integrated circuits, leading to undesired operations and electrical interference.
Innovation Solution
An interface circuit for a switch array that uses a current generator to produce switch array currents with varying magnitudes and a current detector to determine which switch is closed by comparing detected currents with reference currents, reducing electrical interference and power consumption by employing static currents instead of oscillating signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If keyboard interface terminals are positioned close to RF input terminals to achieve high integration, then integration density is improved, but high frequency emissions from the keyboard interface increase and interfere with RF reception
Solution Approach 1:
The patent replaces the conventional voltage-based keyboard scanning system with a current-based system. The current generator supplies different current magnitudes to different row conductors, and the current detector measures these currents to identify pressed keys. This substitution of voltage with current fundamentally changes the operating characteristics, resulting in lower high frequency emissions while maintaining integration density.
Solution Approach 2:
The patent changes the fundamental operating parameter from voltage to current. By using current magnitudes rather than voltage levels to identify row conductors, the system achieves lower electromagnetic emissions. The current generator provides distinct current magnitudes for different rows, and this parameter change resolves the contradiction between integration density and emission levels.
2Volume of moving object
If keyboard interface terminals are positioned close to RF transmitter output to achieve high integration, then integration density is improved, but RF interference into the keyboard interface increases causing spurious signals
Solution Approach 1:
The patent replaces voltage-based sensing with current-based sensing. The current detector measures current magnitudes directly, which are less susceptible to RF interference compared to voltage signals. This substitution allows the keyboard interface to be positioned close to the RF transmitter while maintaining immunity to spurious signals.
Solution Approach 2:
The current generator actively provides known current magnitudes to each row conductor, creating a self-referencing system. The current detector compares measured currents against these known values to identify pressed keys, making the system inherently immune to external RF interference since it relies on active current generation rather than passive voltage sensing.
3Speed
If oscillating signals are used for keyboard scanning to achieve fast response, then response speed is improved, but electrical interference and power consumption increase
Solution Approach 1:
The patent uses periodic scanning of row conductors with different current magnitudes to achieve fast response. The current generator sequentially applies distinct current levels to different rows, and the current detector rapidly identifies which row has a pressed key. This periodic current-based scanning provides fast response without the high frequency emissions associated with oscillating voltage signals.
Data Source
AI summary
An interface circuit for a switch array having an array of switches, each closeable to couple a row conductor of a plurality of row conductors to a column conductor of one or more column conductors, comprises a current generator and a current detector. The current generator has a plurality of row interface ports for coupling to different ones of the row conductors and is arranged to generate a switch array current for coupling to the row interface ports, the switch array current having a different one of a plurality of different switch array current magnitudes for different ones of the row interface ports, and generate one or more reference currents each having a different reference current magnitude. The current detector has one or more column interface ports for coupling to the one or more column conductors and is arranged to detect the switch array current flowing at any one of the one or more column interface ports, and generate a row indication indicative of which of the row conductors a closed one of the switches is coupled to by determining which one of the switch array current magnitudes the detected switch array current has by comparing the detected switch array current with the one or more reference currents.