Class-D Transconductance Amplifier With LC Feedback Extraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional class-D amplifiers operate as voltage-controlled voltage sources, which is not suitable for active multiway loudspeaker applications where direct current control is required to eliminate nonlinear series impedance elements, such as voice coil resistance and inductance.
Innovation Solution
A class-D transconductance amplifier topology is developed with a passive LC reconstruction filter integrated into the feedback loop, operating as a voltage-controlled current source, reducing phase lag and allowing direct current control to the load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a passive LC reconstruction filter is placed within the feedback loop, then audio signal reconstruction is improved, but phase lag increases due to inductor characteristics
Solution Approach 1:
The inductor is extracted from the feedback path while remaining part of the output filter. The feedback signal is taken from before the inductor, eliminating the phase lag introduced by the inductor in the feedback loop, while the inductor still performs its filtering function in the output path.
Solution Approach 2:
The feedback path is segmented from the output filter path. The feedback loop uses a separate path that bypasses the inductor, allowing the reconstruction filter to remain in the output path while the feedback path has minimal phase lag.
2Measurement precision
If a series inductor is placed between the power switch and load, then audio signal reconstruction is improved, but the amplifier complexity increases
Solution Approach 1:
The inductor is merged into the output filter rather than being a separate component in the signal path. The feedback path is combined with the output filter components, using existing capacitors and resistors for feedback without requiring additional active components.
3Ease of manufacture
If conventional voltage-controlled voltage source topology is used, then amplifier design is simplified, but direct current control capability is lost
Solution Approach 1:
The amplifier topology is changed from voltage-controlled voltage source to transconductance amplifier with current feedback. This parameter change enables direct current control capability while maintaining practical design simplicity through the use of passive feedback components.
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 enables stable current-mode operation and efficient audio signal reconstruction, reducing phase lag and nonlinear impedance effects, thereby improving loudspeaker performance.
Implementation Method 1
Low-pass filtering is used to filter the carrier and reconstruct the propagated audio signal at the load.
Implementation Method 2
Together the inductor 122 and the capacitor 124 form a passive LC reconstruction filter 128. The passive LC reconstruction filter 128 acts as a low-pass filter to remove the high-frequency PWM carrier signal and reconstruct the audio signal
Implementation Method 3
The operational amplifier 110 is configured as an integrator with a feedback network 114 and the input resistor 106.
Implementation Method 4
Class-D amplifiers are also known as 'switched mode' amplifiers because they operate by switching transistors, such as field effect transistors (FETs), at a carrier frequency to create a switched carrier signal. The switched carrier signal is typically a pulse width modulated (PWM) signal
Data Source
AI summary
The invention relates to a class-D audio amplifier. The class-D audio amplifier is configured in a current feedback mode as a voltage-controlled current source and a passive inductor/capacitor (LC) reconstruction filter. A portion of the passive LC reconstruction filter is situated in a feedback loop to an error amplifier.