Audio Output Stage Using Rechargeable Capacitor Voltage Boost
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Solution Overview
Problem
Conventional output stages in mobile devices, such as mobile telephones, face limitations in achieving enhanced audio output amplitude without increasing the complexity and cost of integrated circuit fabrication, particularly when operating within a narrow voltage range and requiring efficient voltage swing across transducers.
Innovation Solution
An output stage utilizing a rechargeable energy store, such as a capacitor, is selectively connected between the output node and a second voltage supply, allowing the voltage at the output node to be driven outside the range defined by the primary supply voltages, enabling enhanced audio output amplitude without complex fabrication processes. The rechargeable store is recharged during negative half cycles, and the recharge process is managed to minimize performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a DC blocking capacitor is included at the output node to shift the peak to peak voltage range, then the lower frequency bandwidth is improved, but the capacitor size becomes large (330 micro Farads) representing high implementation cost
Solution Approach 1:
The patent transforms the static capacitor into a dynamic rechargeable energy store that can be periodically recharged during negative half cycles. This dynamic approach allows the system to achieve the same voltage shifting effect with a much smaller capacitor, as the energy is replenished over time rather than requiring a large static capacitance value.
Solution Approach 2:
The rechargeable energy store is recharged periodically during negative half cycles of the audio signal. This periodic recharging allows the system to maintain the voltage swing enhancement effect continuously while using a small capacitor that is replenished in discrete periodic intervals, avoiding the need for a large 330 micro Farad capacitor.
2Power
If a charge pump is used to generate a negative reference voltage to increase output amplitude, then the voltage swing is improved, but the integrated circuit complexity and fabrication cost increase significantly
Solution Approach 1:
The patent introduces a rechargeable energy store as an intermediary element between the output node and the second voltage supply. This intermediary component enables voltage swing enhancement without requiring complex charge pump circuits or multiple voltage supplies, as the energy store acts as a simple buffer that can be periodically recharged using standard CMOS transistors.
Solution Approach 2:
The rechargeable energy store serves itself by being recharged during negative half cycles through the action of the second transistor. This self-service mechanism eliminates the need for external charge pump circuits or additional voltage generation hardware, as the system uses its own operating cycles to replenish the energy store.
3Adaptability or versatility
If the entire integrated circuit is run between V+ and V- voltages to overcome substrate voltage limitations, then the output transistor can connect to negative reference voltage, but the voltage difference across the integrated circuit increases leading to increased power dissipation and shortened battery life
Solution Approach 1:
The patent applies local quality by implementing the negative voltage capability only at the specific location where it is needed (the output transistor connection to the rechargeable energy store) rather than throughout the entire integrated circuit. The rest of the circuit continues to operate within the standard 0V to V+ range, minimizing the overall voltage difference and power dissipation while still achieving the desired output amplitude enhancement.
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
This solution allows for increased peak-to-peak voltage swing while maintaining the output stage within conventional CMOS fabrication processes, enhancing audio output amplitude in mobile devices without increasing power dissipation or fabrication complexity, and the rechargeable energy store effectively doubles the efficiency of the system by storing more charge than physically possible for a given potential difference.
Implementation Method 1
a rechargeable energy store having a potential difference between first and second terminals
Data Source
AI summary
An output stage, comprising a first transistor operable to pull a voltage at an output node towards a first voltage, and a rechargeable energy store having a potential difference between first and second terminals wherein the rechargeable energy store is arranged to be controllably connected between the output node and a second voltage supply such that the voltage at the output node can be driven to a voltage outside of a range defined between the first and second voltages.