Dual Amplifier DC Bias Alignment for Noise-Free Gain Switching
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Solution Overview
Problem
Existing amplifier arrangements for analog audio signals face issues with signal interference due to phase differences between amplifier branches, especially when switching between high and low gain settings, which limits the usable dynamic range and introduces noise.
Innovation Solution
A DC coupled dual amplifier arrangement with a differentiating element and feedback loop to regulate the DC voltage component of the input signal, ensuring both amplifier branches have the same DC component, thus eliminating phase differences and allowing seamless switching without interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If DC coupling is used to eliminate phase differences between amplifier branches, then signal interference during switching is reduced, but DC voltage deviations generate significant deviations at the switchover point leading to interference
Solution Approach 1:
A feedback loop is implemented that detects DC voltage deviations in the analog signal path and automatically compensates for them. The feedback mechanism monitors the DC voltage level and adjusts it to maintain consistency between amplifier branches, preventing interference at the switchover point while preserving the benefits of DC coupling.
Solution Approach 2:
The patent changes the DC voltage parameter of the input signal to a predetermined value that ensures consistent DC components across both amplifier branches. By carefully selecting and maintaining this specific DC voltage level, the system eliminates deviations at the switchover point while keeping the DC coupled architecture intact.
2Object-generated harmful factors
If coupling capacitors are used between amplifier stages, then DC voltage deviations are blocked, but phase differences occur between amplifier branches leading to clicking noise during switching
Solution Approach 1:
The patent removes coupling capacitors from the signal path and replaces them with direct DC coupling between amplifier stages. By extracting the capacitive elements that cause phase shifts, the system achieves seamless signal transmission between stages while managing DC voltage levels through feedback control instead of passive blocking.
Solution Approach 2:
The patent substitutes the mechanical/electrical function of coupling capacitors (which block DC and pass AC signals) with an active feedback control system. The feedback mechanism electronically regulates DC voltage levels, replacing the passive capacitive blocking function with an active control approach that maintains signal integrity across the full frequency range.
Data Source
AI summary
For converting analog audio signals captured by a microphone into digital audio data, the analog audio signals are first amplified in a pre-amplifier and then fed to an analog-to-digital converter (ADC). For better utilizing the dynamic range of the ADC, a DC coupled dual amplifier circuit may be used herein that automatically switches between two amplifier branches with different gain factors. To avoid switching noise, both signals must have the same DC component before the analog-to-digital conversion. To achieve this, the amplifier arrangement comprises a first amplifier branch having a higher first gain factor (G1) and providing a first output voltage (VOUT1) and a second amplifier branch having a lower second gain factor (G2) and providing a second output voltage (VOUT2). Both amplifier branches are DC coupled and receive as a common input signal an audio signal with a predetermined DC component (Vk). The amplifier arrangement further comprises a differentiating member (D) for generating a voltage difference between the two output voltages (VOUT1,VOUT2). From the voltage difference, a control voltage (Vbias) is generated for controlling the DC component (Vk) of the input signal such that the DC components of the output voltages (VOUT1, VOUT2) are aligned to each other.