AGC Sub-circuit Noise Gate for Credit Card Reader Signal Stability
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Solution Overview
Problem
Automatic gain control (AGC) circuitry in host devices amplifies both intentional and unintentional signals on the audio input channel, leading to false detection of payment information from credit card readers, causing errors and unnecessary processing due to spurious or random noise signals.
Innovation Solution
Introducing an intentional noise signal with specific characteristics into the audio input channel to stabilize the AGC gain, preventing amplification of spurious noise signals while ensuring proper amplification of data signals from credit card readers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AGC circuitry amplifies all signals on the audio input channel, then detection sensitivity is improved, but false detection of spurious noise signals increases
Solution Approach 1:
A noise gate circuit is introduced as an intermediary component between the AGC circuitry and the audio input channel. This noise gate acts as a mediator that selectively blocks spurious noise signals while allowing intentional signals to pass through to the AGC amplifier, thereby preventing false detection without compromising detection sensitivity for valid signals.
Solution Approach 2:
The signal processing function is segmented into two distinct stages: first, the noise gate circuit segments and filters out spurious noise signals before they reach the AGC amplifier; second, the AGC amplifier processes only the remaining intentional signals. This segmentation allows each component to specialize in its function, improving overall system reliability while maintaining detection sensitivity.
2Measurement precision
If AGC gain is increased to amplify weak signals, then signal detection capability is improved, but amplification of spurious noise signals worsens
Solution Approach 1:
The noise gate circuit serves as a protective intermediary that blocks spurious noise signals from reaching the high-gain AGC amplifier. By placing this intermediary in the signal path, the system can maintain high AGC gain for weak signal amplification while the noise gate prevents harmful noise signals from being amplified along with the valid signals.
Solution Approach 2:
The noise gate circuit converts the potentially harmful effect of high gain amplification into a benefit by selectively allowing only intentional signals to be amplified. The circuit uses the high gain capability beneficially for weak signal detection while the noise gate transforms what would otherwise be harmful noise amplification into a controlled filtering function.
Data Source
AI summary
Aspects of the subject disclosure provide a reader device for managing operation of an automatic gain control (AGC) sub-circuit on a host device computing device. In some implementations, a reader device of the subject technology can include a controller, a noise generator, noise coupling circuitry, and a 3.5 mm audio plug including an audio bus that is configured for insertion into a headphone port of a host device, such as a smart phone or tablet computer. Upon connection of the reader device to the host computing device, the reader device can provide an intentional noise signal to the host device via a signal path where the intentional noise signal is configured to establish a substantially stable gain amount at the AGC sub-circuit.