I/O Multiplexer Bus for Capacitance Sensing
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Solution Overview
Problem
Conventional integrated circuits with capacitance sense functions are hardwired to a single input/output port, lacking flexibility to be coupled to a selectable port, limiting their ability to multiplex and measure capacitance changes across multiple ports effectively.
Innovation Solution
An input/output multiplexer bus system that time-multiplexes or time-shares capacitance measuring circuits across general-purpose I/O ports, enabling flexible coupling of various capacitance sensing techniques, such as relaxation oscillator and charge transfer methods, using programmable switch logic to divert currents and voltages, allowing for sequential measurement of multiple capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitance sensing circuits are hardwired to a single input/output port, then the circuit design is simple and reliable, but the system lacks flexibility and cannot multiplex multiple ports
Solution Approach 1:
The capacitance sensing circuit is designed to serve multiple I/O ports through time-multiplexing. A single sensing circuit can be sequentially connected to different ports via programmable switch logic, allowing one circuit to perform the function of multiple dedicated circuits. This achieves port flexibility without proportionally increasing circuit complexity.
Solution Approach 2:
The system uses dynamic switching of I/O ports through programmable switch logic controlled by a microcontroller. The capacitance sensing circuit can be dynamically reconfigured to connect to different ports based on measurement needs, enabling flexible multiplexing while maintaining a relatively simple overall circuit architecture.
2Productivity
If multiple dedicated capacitance sensing circuits are used for each port, then each port can be measured independently and simultaneously, but the device complexity and resource consumption increase
Solution Approach 1:
The system implements periodic sequential measurement of multiple ports using time-multiplexing. The programmable switch logic cycles through different port connections in a periodic manner, allowing the single capacitance sensing circuit to measure multiple ports over time. This achieves comprehensive measurement coverage without requiring multiple simultaneous sensing circuits.
Solution Approach 2:
Multiple port measurement functions are merged into a single capacitance sensing circuit through time-multiplexing. Instead of having separate dedicated circuits for each port, the system combines all port measurements into one shared circuit that is sequentially connected to different ports, reducing the total number of sensing circuits while maintaining measurement capability.
3Device complexity
If a single capacitance sensing circuit is time-multiplexed across multiple ports, then device complexity is reduced, but measurement speed and simultaneous measurement capability are limited
Solution Approach 1:
The system uses dynamic port switching controlled by programmable switch logic to enable rapid sequential measurement. The switching mechanism allows the single capacitance sensing circuit to quickly transition between ports, improving measurement speed compared to static configurations while maintaining device simplicity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables flexible and efficient multiplexing of capacitance sensing circuits across multiple ports, enhancing the ability to monitor and measure capacitance changes, thereby improving the usability and versatility of capacitance sense interfaces in integrated circuits.
Implementation Method 1
The relaxation oscillator begins by charging the DUT capacitor from a ground potential or zero voltage and continues to accumulate charge on the DUT capacitor at a fixed charging current Ic until the voltage across the DUT capacitor reaches a reference voltage (Vref). At Vref, the relaxation oscillator allows the accumulated charge to discharge or the DUT capacitor to 'relax' back to the ground potential
Implementation Method 2
The frequency comparator is coupled to receive RO CLK and REF CLK, compare their frequencies fRO and fREF, respectively, and output a signal indicative of the difference Δf between these frequencies. By monitoring Δf one can determine whether the capacitance of the DUT capacitor has changed.
Implementation Method 3
Once DUT capacitor 120 charges to the supply voltage VS, the charge on DUT capacitor 120 is transferred onto summing capacitor 110 and distributed between the two capacitors. Charge transfer occurs by asserting φ1 and φ2 to open circuit switches SW1 and SW2, respectively, and asserting φ0 to close circuit switch SW0.
Data Source
AI summary
One embodiment includes and I/O bus including a signal line coupled to a signal source and multiple line switches, each line switch to couple a corresponding I/O port to the signal line. Switch logic coupled to the I/O bus may programmatically switch the multiple line switches to couple at least one of the signal source and measurement circuitry to the respective I/O port.