Digital Amplifier Gain Control via Frequency Filtering
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Solution Overview
Problem
Existing digital amplifiers use unnecessary frequency band components in the power supply voltage waveform for gain control, leading to adverse effects on sound reproduction due to waveform distortion and inappropriate timing in gain control.
Innovation Solution
A digital amplifier design that includes a pulse generating unit, a switching circuit, and a filter unit with a variable frequency transfer characteristic to limit specific frequency band components in the power supply voltage waveform, preventing the use of high-frequency noise for gain control and ensuring proper sound reproduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power supply voltage waveform is fed back directly to the control circuit for gain control, then the gain can be kept constant, but unnecessary frequency band components including switching noise are also used for control which adversely affects sound reproduction
Solution Approach 1:
A filter unit is introduced as an intermediary component between the power supply voltage waveform and the control circuit. This filter selectively removes unnecessary high-frequency band components (including switching noise) while allowing the necessary frequency components to pass through to the control circuit for gain stabilization, thus preventing sound reproduction degradation
2Speed
If high-frequency components in the power supply voltage waveform are used for gain control, then the response speed is improved, but waveform distortion occurs and sound reproduction quality deteriorates
Solution Approach 1:
The filter unit changes the frequency parameter of the power supply voltage waveform by selectively attenuating high-frequency components while preserving lower frequency components. This parameter modification allows the control circuit to operate with cleaned voltage feedback, achieving both adequate response speed and waveform accuracy without distortion
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 effectively prevents waveform distortion and ensures stable gain control by isolating high-frequency noise, allowing only necessary frequency components to influence the gain, thereby improving sound reproduction quality.
Implementation Method 1
a filter unit that limits a specific frequency band component in a power supply voltage waveform of the power supply to generate the control signal
Data Source
AI summary
Switching circuits constituted by FETs are inserted between power supplies +VB and −VB and a speaker serving as a load respectively, and switched on/off by a pulse train so as to drive the speaker. A pulse generation circuit is a circuit by which a pulse train subjected to pulse width modulation in accordance with an input signal is supplied to the switching circuits. The pulse generation circuit can control the amplitude of the pulse train in accordance with a control signal. Filters limit specific frequency band components in a power supply voltage waveform between the power supplies, and supply the power supply voltage waveform to a gain control circuit in the pulse generation circuit as the control signal.