Muting Circuit with Matched DC Offset for Quiet Switching
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Solution Overview
Problem
Conventional muting circuits in electronic volumes generate noise due to DC voltage fluctuations caused by internal circuit characteristics and manufacturing variations of ICs, resulting in audible noise during the muting process.
Innovation Solution
A muting circuit with a DC offset eliminating unit using a High Pass Filter and a muting signal generating unit with a second operational amplifier to eliminate and replicate DC offsets, combined with a selecting unit that manages analogue switches to maintain a constant DC level, reducing noise fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional muting circuit switches analogue switches between on and off states, then muting process can be executed, but DC voltage fluctuations occur causing audible noise
Solution Approach 1:
The muting signal generating unit proactively generates a muting signal with predetermined DC level before the switching occurs. This preliminary preparation of the muting signal ensures that when the analogue switches transition, the output maintains a stable DC level, preventing DC voltage fluctuations and the resulting audible noise during the muting process.
Solution Approach 2:
The muting signal acts as an intermediary between the input signal and the output during the switching transition. By introducing this intermediate muting signal with controlled DC level, the circuit avoids direct connection between the input signal and output during switching, thereby eliminating DC voltage fluctuations and audible noise while maintaining reliable muting functionality.
2Ease of operation
If AC-GND level is used as predetermined DC level for muting, then muting process can be implemented, but DC offset variations cause noise generation
Solution Approach 1:
The invention changes the DC level parameter of the muting signal from the conventional AC-GND level to a predetermined DC level that is optimized to match the input signal's DC characteristics. This parameter change eliminates DC offset variations during switching, preventing noise generation while maintaining ease of muting process implementation through simple switch control.
3Adaptability or versatility
If analogue switches are used for muting control, then muting function can be achieved, but switching transitions cause DC voltage fluctuations
Solution Approach 1:
The muting signal is prepared in advance with a predetermined DC level that matches the expected output conditions. This preliminary preparation ensures that when the analogue switches transition between states, the DC voltage remains stable because the muting signal already establishes the correct voltage level, preventing fluctuations during the switching process while maintaining muting adaptability.
Solution Approach 2:
The muting signal serves as an intermediary that stabilizes the DC voltage during analogue switch transitions. By introducing this intermediate signal with controlled DC characteristics, the circuit maintains voltage stability during switching operations, eliminating the DC voltage fluctuations that would otherwise occur due to the switching action itself.
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 eliminates DC offsets and maintains a constant DC level, reducing both inaudible and audible noise during muting, enhancing the noise-free performance of electronic volumes.
Implementation Method 1
a DC offset eliminating unit including an HPF (High Pass Filter) constituted by a first operational amplifier to eliminate a DC offset component of an AC input signal
Data Source
AI summary
A muting circuit comprising: a DC offset eliminating unit including an HPF (High Pass Filter) constituted by a first operational amplifier to eliminate a DC offset component of an AC input signal, the DC offset eliminating unit being configured to output an output signal obtained by eliminating the DC offset component of the AC input signal; a muting signal generating unit including a second operational amplifier configured to generate a second DC offset identical in level to a first DC offset at the first operational amplifier, the muting signal generating unit being configured to output a muting signal indicative of the second DC offset by fixing input to the second operational amplifier at a predetermined DC level; and a selecting unit configured to select and output the output signal when muting is not executed, and to select and output the muting signal when muting is executed.