BTL Amplifier Circuit With Impedance Buffer for Low Noise Output
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional BTL power amplifiers suffer from low oscillation stability and inability to achieve large maximum output power due to high noise and offset voltage issues, which deteriorate sound quality and require high accuracy in gm amplifier elements, making them unsuitable for low noise and low offset applications.
Innovation Solution
The proposed BTL power amplifier circuit includes a first and second operational amplifier with feedback resistance elements, a voltage dividing circuit, and an impedance conversion circuit, eliminating the need for a gm amplifier, thereby reducing noise and offset while maintaining oscillation stability through a buffer amplifier configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a gm amplifier is used for voltage-current conversion in a conventional BTL power amplifier, then the circuit structure can be simplified, but noise and offset voltage are amplified leading to deteriorated sound quality and increased POP noise
Solution Approach 1:
The invention extracts and removes the gm amplifier from the circuit by implementing voltage-current conversion directly within the operational amplifier circuits themselves. This eliminates the source of noise and offset voltage amplification while maintaining the necessary functional capability for BTL operation.
Solution Approach 2:
The invention introduces intermediary feedback circuits and resistance elements that mediate between the input signal and output stages. These intermediary components enable precise control of the conversion gain while preventing the amplification of noise and offset voltage, effectively decoupling the voltage-current conversion function from the problematic gm amplifier stage.
2Manufacturing precision
If high accuracy is required for elements forming the gm amplifier to attain low offset voltage, then offset voltage decreases, but chip area of the gm amplifier increases
Solution Approach 1:
By removing the gm amplifier entirely and implementing voltage-current conversion within standard operational amplifier circuits, the invention eliminates the need for high-precision gm amplifier elements. This approach achieves low offset voltage without requiring large chip area dedicated to precision gm amplifier components.
Solution Approach 2:
The invention employs feedback circuits with precisely controlled resistance elements to achieve accurate voltage-current conversion. The feedback mechanism allows for precise control of conversion gain using standard precision resistors, avoiding the need for complex high-accuracy gm amplifier element fabrication while maintaining low offset voltage performance.
3Stability of the object's composition
If feedback quantity is fixed in conventional BTL power amplifiers, then oscillation stability is excellent, but the amplifier cannot achieve large maximum output power
Solution Approach 1:
The invention introduces dynamic elements into the feedback circuits, allowing the feedback quantity to vary with signal conditions. The feedback resistance elements are configured to provide different feedback levels depending on the operating state, enabling the circuit to maintain stability during normal operation while achieving high output power when needed. This dynamic feedback adjustment resolves the contradiction between fixed stability and variable power output capability.
Data Source
AI summary
An amplifier circuit of a BTL system is disclosed, which comprises a first operational amplifier which outputs an output signal having a same phase as an input signal input to a signal input terminal, a second operational amplifier which outputs an output signal having an opposite phase to the input signal, a voltage divider which generates a midpoint voltage of the input signal, a first resistor connected between an output terminal and a negative phase input terminal of the first operational amplifier, second and third resistors connected in series between the negative phase input terminals of the first and second operational amplifiers, a fourth resistor connected between an output terminal and the negative phase input terminal of the second operational amplifier, and an impedance converter connected between a midpoint voltage node of the voltage divider and a series-connection node of the second and third resistors.