Push-Button Switch Interface Circuit for Nanoamp Power and RFI Immunity
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Solution Overview
Problem
Existing switch interface circuits for mobile applications, such as smart cards, face challenges in minimizing power consumption while maintaining low impedance to prevent RFI interference and allowing extended switch-closed operation.
Innovation Solution
A switch interface circuit design incorporating an inverting comparator circuit with hysteresis, an edge-triggered switching mechanism, and specific resistive elements, along with an NMOS transistor and D-type flip-flop, to achieve low supply current and low impedance when the switch is closed, and zero current when open, utilizing edge-triggered detection for extended operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switch interface circuit uses a low impedance path to prevent RFI interference, then the reliability is improved, but the power consumption increases
Solution Approach 1:
The circuit dynamically changes the impedance state based on switch position. When the push-button switch is open, the circuit maintains a low impedance path to ground through the NMOS transistor and resistor network to prevent RFI interference. When the switch is closed, the circuit transitions to a high impedance state to minimize power consumption, allowing the battery to last longer in mobile applications.
Solution Approach 2:
The circuit changes the electrical parameter (impedance) based on operational conditions. The NMOS transistor is controlled to switch between conductive and non-conductive states, thereby changing the equivalent impedance seen by the input terminal. This parameter change allows the circuit to optimize between RFI prevention and power consumption depending on the switch state.
2Duration of action of stationary object
If the circuit consumes minimal current to extend battery life, then the duration of action is improved, but the ability to maintain low impedance increases difficulty
Solution Approach 1:
The circuit replaces a continuously active low-impedance path with a controlled electronic switching mechanism. Instead of using a mechanical switch that would continuously draw current, the invention uses an NMOS transistor controlled by a voltage-dependent resistor network to create an electronic equivalent that only draws minimal current while maintaining the same RFI prevention function.
Solution Approach 2:
The voltage-dependent resistor network acts as an intermediary between the push-button switch and the NMOS transistor. This intermediary component translates the mechanical switch state into a control voltage that gates the NMOS transistor, thereby indirectly controlling the impedance state without requiring the transistor to be directly driven by the mechanical switch.
3Duration of action of stationary object
If the circuit allows extended switch-closed operation, then the duration of action is improved, but the power consumption management becomes more difficult
Solution Approach 1:
The circuit performs preliminary detection of the switch closure event through the inverting comparator with hysteresis. This preliminary action generates a clean digital signal that triggers the edge-triggered D-type flip-flop, which then latches the state and allows the circuit to enter a low-power holding mode. This preliminary detection and latching mechanism enables extended operation by separating the detection function from the continuous monitoring requirement.
Solution Approach 2:
The edge-triggered detection mechanism operates periodically at the clock edge of the D-type flip-flop rather than continuously monitoring the switch state. This periodic sampling approach reduces power consumption compared to continuous monitoring while still capturing switch events accurately, thereby enabling extended switch-closed operation with reduced power draw.
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
The solution enables ultra-low power consumption of a few tens of nanoamps during switch closure, maintains low impedance to prevent RFI interference, and allows for extended switch-closed operation, minimizing energy loss and ensuring reliable operation.
Implementation Method 1
an inverting comparator circuit with hysteresis
Implementation Method 2
an NMOS transistor, a logic inverter, and a D-type flip-flop
Implementation Method 3
edge-triggered detection of the switch event
Data Source
AI summary
Circuits and methods to achieve a switch interface circuit for a single pole, single throw (SPST) momentary push-button switch consuming a few tens of nanoamps whilst the push-button switch is closed, having low impedance input path when the switch is open in order to eliminate RFI interference have been achieved. The two states of the push-button switch, open and closed, maintain a low impedance path to one of the power supplies. The supply current is zero when the switch is open and is minimized whilst the switch is closed. The asynchronous edge triggered detection of the switch event allows an extended switch open to closed transition operation.