AC-Coupled Level Shifting Circuit for Duty Cycle Integrity
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Solution Overview
Problem
Conventional techniques for enabling communication between payment terminal components with different operating voltages often result in unstable or inaccurate signal transmission due to insufficient voltage levels and asymmetric rising and falling times, leading to errors in payment transactions.
Innovation Solution
A level shifting circuit within the payment terminal's reader chip, utilizing a self-biased inverter and capacitor for AC coupling, adjusts low voltage signals to higher levels while maintaining the duty cycle, ensuring accurate signal transmission across components with varying voltage requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional level shifting techniques are used to raise voltage levels, then voltage level is improved, but signal accuracy and duty cycle are degraded
Solution Approach 1:
The patent introduces an AC coupling capacitor as an intermediary element between the low-voltage signal source and the high-voltage level shifter. This capacitor blocks DC components while allowing AC signal components to pass, enabling voltage level translation without distorting the signal waveform or duty cycle. The capacitor acts as a mediator that separates the voltage shifting function from the signal integrity function.
Solution Approach 2:
The patent changes the operating parameters of the level shifter by AC-coupling the input signal, which removes the DC offset and allows the level shifter to operate around a mid-rail voltage point. This parameter change enables the level shifter to symmetrically swing between high and low states, maintaining equal rising and falling times while operating at higher voltage levels.
2Use of energy by moving object
If conventional level shifting techniques are used, then voltage level is improved, but communication reliability is degraded
Solution Approach 1:
The AC coupling capacitor serves as a mediator that prevents DC voltage mismatches from causing communication errors. By blocking DC components and allowing only AC signal variations to pass, the capacitor ensures that the signal transitions are clean and well-defined, improving communication reliability between components with different voltage domains.
Solution Approach 2:
The patent employs a self-biased inverter configuration where the output is fed back to the input through a resistor network. This feedback mechanism automatically establishes the correct operating point and ensures that the inverter switches cleanly between logic states, enhancing signal integrity and communication reliability in the voltage-translated domain.
3Use of energy by moving object
If conventional level shifting techniques are used, then voltage level is improved, but signal symmetry is degraded
Solution Approach 1:
The patent changes the biasing parameters by AC-coupling the input, which centers the signal around a mid-rail voltage rather than a rail-to-rail voltage. This parameter change allows the inverter to switch symmetrically between high and low states, creating equal rise and fall times while operating at the higher voltage level required by the receiving component.
Solution Approach 2:
The patent intentionally introduces asymmetry in the biasing network (through the feedback resistor values) to compensate for inherent transistor asymmetries, achieving overall signal symmetry. The feedback network is designed with specific resistor ratios that balance the pull-up and pull-down strengths, ensuring symmetric switching behavior despite the asymmetric physical implementation of the inverter transistors.
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 ensures stable and accurate communication between payment terminal components, preventing errors and enhancing the reliability of payment transactions by effectively shifting low voltage signals to higher levels without altering the duty cycle.
Implementation Method 1
The level shifting circuit AC couples the input signal to an inverter that is self-biased at a threshold voltage
Data Source
AI summary
A level shifting circuit can be used to adjust the level of the input signal to a desired output level while maintaining the duty cycle of the input signal. The level shifting circuit can include a capacitor to AC couple the input signal to an inverter that is self-biased at the threshold voltage for the inverter. The AC coupling of the input signal permits the input signal to “ride on” the threshold voltage and transition the inverter between states depending on the value of the input signal. The inverter can be biased at the threshold voltage by connecting the output of the inverter in feedback with the input of the inverter using one or more resistors.