Self-Biasing Output Booster Amplifier for Stable High-Pass Filtering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electronic filter arrangements in hearing devices suffer from a non-constant cut-off frequency with input signal level, leading to poor sound quality and high noise levels due to resistance biasing and the use of common source NMOS output stages.
Innovation Solution
A self-biasing output booster amplifier with a high-pass filter stage that maintains a stable frequency response by using current mirrors and a source follower configuration, allowing internal bias current balancing through a negative feedback path, reducing supply current efficiency, and incorporating a PMOS or NMOS transistor for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If resistance biasing is used at the input stage of the amplifier, then the amplifier can operate with simple biasing, but the cut-off frequency becomes non-constant with input signal level
Solution Approach 1:
The patent implements a feedback mechanism where the output signal is fed back to the input stage through a feedback resistor. This feedback path compensates for the signal level variations, maintaining a constant cut-off frequency by adjusting the effective biasing conditions dynamically in response to output variations.
Solution Approach 2:
The patent changes the biasing parameter from a fixed resistance value to a dynamically adjustable impedance that varies with signal level. By using an active circuit element (such as a transistor or operational amplifier) configured to provide negative feedback, the effective resistance at the input stage is automatically adjusted to maintain constant cut-off frequency across different signal levels.
2Power
If a common source NMOS output stage is used, then the amplifier can provide high gain, but the output noise level becomes high
Solution Approach 1:
The patent employs a current mirror configuration that copies the input signal current to the output stage. By using matched transistors in the current mirror, the signal is replicated with high fidelity while the noise contribution from the output stage is minimized through careful matching and biasing of the mirror transistors.
Solution Approach 2:
The patent introduces an intermediate stage between the input and output stages that acts as a buffer. This intermediate stage, configured as a voltage follower or unity gain amplifier, isolates the high-gain output stage from the input signal source, preventing noise amplification while maintaining signal integrity.
3Object-affected harmful factors
If the amplifier is designed for high-pass filtering function, then low frequency signals can be attenuated, but the filter function is lost when large low frequency signals are introduced
Solution Approach 1:
The patent implements a dynamic high-pass filter where the cut-off frequency is automatically adjusted based on the input signal level. When large low-frequency signals are detected, the circuit dynamically shifts the cut-off frequency to maintain attenuation, whereas for small signals the cut-off frequency remains at its nominal value. This is achieved through signal-level-dependent impedance modulation in the filter network.
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 2c
AI summary
The present invention relates to a self-biasing output booster amplifier (200) comprising an input amplifier stage (201), an output amplifier stage (206) being operatively connected to an output of the input amplifier stage, and first (203) and second (202) current copying circuits, wherein the second current copying circuit (202) is biased from an output of the self-biasing output booster amplifier (+). The first (203) and second (203) current copying circuits are configured to copy at least a portion of the current (Ios) through the output amplifier stage (206). The sum of the output of the second current copying circuit (202) and the output of the output amplifier stage (206) provides the output current (Isource - Io) of the self-biasing output booster amplifier (200), Finally, the input amplifier stage (201) is biased from the output of the second current copying circuit (202).