Subsonic Test Signal Circuit for Inaudible Audio Calibration
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Solution Overview
Problem
Existing audio subsystem calibration tests in electronic devices often produce annoying tones or clicks, leading users to believe the device is not functioning properly, and require large external components or additional IC pins for filtering, which are impractical for integrated circuits.
Innovation Solution
An electronic circuit incorporating a capacitor, current generating circuit, and current pulse timing circuit that generates a pseudo-sinusoidal pulse signal by varying current pulse durations between minimum and maximum duty cycles, producing a subsonic frequency tone inaudible to users, without the need for large external components or additional IC pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional calibration tests use audible tones, then the test can be performed effectively, but the user experiences annoyance and may believe the device is malfunctioning
Solution Approach 1:
The patent changes the frequency parameter of the test signal from the audible range to the subsonic range (below 20 Hz). This parameter change allows the calibration test to proceed effectively while the signal becomes inaudible to human ears, thereby eliminating user annoyance while maintaining test reliability
2Manufacturing precision
If filtering is applied to suppress audible harmonics, then the test signal becomes cleaner, but large external components or additional IC pins are required
Solution Approach 1:
Instead of generating an audible tone and filtering out unwanted harmonics, the patent inverts the approach by directly generating a subsonic frequency signal. This inversion eliminates the need for filtering circuits and large external components, as the fundamental frequency itself is already in the inaudible subsonic range
Solution Approach 2:
The patent extracts only the essential calibration function by using a direct subsonic signal generation approach, removing the need for complex filtering circuits and large external components that would be required in traditional audible tone methods
Data Source
AI summary
An apparatus includes a capacitor, a current generating circuit communicatively coupled to the capacitor, and a current pulse timing circuit communicatively coupled to the current source circuit. The current timing pulse circuit is configured to time durations of a first plurality of current pulses from the current generating circuit for charging the capacitor and a second plurality of current pulses for discharging the capacitor, and step the durations of the current pulses between a minimum duty cycle and a maximum duty cycle. A cycle of providing the first plurality of current pulses and providing the second plurality of current pulses results in generation of a subsonic pseudo-sinusoidal pulse signal at the capacitor.