Audio Charge Pump Mode Switching for Low-Signal Efficiency
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Solution Overview
Problem
In battery-operated consumer audio devices, charge-pump power supplies waste power during low signal levels due to high internal consumption, which reduces overall efficiency, especially when used with linear power amplifiers.
Innovation Solution
A charge-pump power supply with selectable operating modes adjusts the size and frequency of switching transistors based on signal amplitude, using multiple transistor banks and gate capacitance management to optimize efficiency and power output, allowing for higher efficiency during low signal levels and increased power output during high signal levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the charge pump operates at high power output capability, then the power delivery to the audio amplifier is sufficient, but the internal power consumption increases and efficiency decreases during low signal levels
Solution Approach 1:
The charge pump circuit dynamically adjusts its operating parameters including switching frequency and transistor effective size based on the signal level detected from the audio amplifier output. During low signal levels, the circuit reduces switching frequency and transistor effective size to minimize internal power consumption. During high signal levels, it increases these parameters to provide sufficient power output capability.
Solution Approach 2:
The invention changes key operating parameters of the charge pump circuit based on signal level conditions. The switching frequency is varied from a first frequency during low signal levels to a second frequency during high signal levels. Additionally, the effective size of switching transistors is adjusted by selectively enabling or disabling parallel transistor configurations, thereby optimizing the balance between power consumption and power delivery capability.
2Power
If the charge pump uses larger switching transistors for high power capability, then power delivery is improved, but gate capacitance increases and switching losses increase
Solution Approach 1:
The switching transistor structure is segmented into multiple parallel transistors that can be independently controlled. Instead of using a single large transistor, the circuit employs multiple smaller transistors connected in parallel, where only the necessary number are activated based on signal level requirements. This segmentation reduces the total gate capacitance that needs to be charged and discharged during switching operations.
Solution Approach 2:
The circuit activates only the necessary portion of the available transistor banks based on the signal level requirements. During low signal levels, fewer transistors are activated, using only the partial capability needed. During high signal levels, more transistors are activated to provide the excessive power capability required for high-demand scenarios.
Data Source
AI summary
A charge pump power supply for a consumer device audio power stage has an efficiency selected according to signal level. The frequency of operation of the charge pump and/or the effective size of a switching transistor bank is adjusted based upon a volume (gain) setting, or a detected signal level, so that internal power consumption of the charge pump is reduced when high output current is not required from the audio power stage and consequently from the charge pump. Operating modes of the charge pump are selected by the signal level indication and include at least a high power and a high efficiency mode selected by setting the charge pump operating frequency and/or enabling or disabling switching of one or more of multiple parallel transistors used to implement each switching element of the charge pump, thereby setting the level of gate capacitance being charged/discharged by the gate driver circuit(s).