Bipolar Amplifier Output Stage With Beta Equalization for Low Distortion
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Solution Overview
Problem
Amplifiers suffer from non-linear distortions due to the characteristics of bipolar transistors, leading to even-order non-linear distortions that affect output signals, particularly in low and mid-frequency regions, and increasing the gain bandwidth product to mitigate these distortions is power-intensive, making it impractical in low-power environments.
Innovation Solution
An output stage circuit with a first and second set of output transistors and an auxiliary buffer circuit that equalizes the current gain of the transistors to correct even-order non-linear distortions without significantly increasing power consumption, using a five-pack differential to single-ended stage amplifier configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the amplifier's gain bandwidth product (GBP) is increased to reduce non-linear distortions, then the distortion level decreases, but the power consumption increases significantly
Solution Approach 1:
The output stage is divided into two separate sets of transistors: a first set handling positive half-cycles and a second set handling negative half-cycles. This segmentation allows independent optimization of each set's current gain, enabling distortion reduction without requiring a high GBP across the entire amplifier bandwidth.
Solution Approach 2:
The patent applies different current gain values to different transistor sets based on their specific function. The first set of transistors has a first current gain value optimized for positive half-cycles, while the second set has a second current gain value optimized for negative half-cycles. This local optimization reduces even-order distortions without requiring a uniform high GBP throughout the amplifier.
2Power
If bipolar transistors are driven into saturation or cut-off to increase amplification, then the amplification capability improves, but non-linear behavior and signal distortions increase
Solution Approach 1:
The patent deliberately creates an asymmetric output stage where the first set of transistors and second set of transistors have different current gain values. This asymmetric design allows each transistor set to operate in its optimal region without being driven into saturation or cut-off, thereby maintaining high amplification capability while minimizing non-linear distortions that would otherwise result from asymmetric switching behavior.
Data Source
AI summary
Reducing non-linear distortions of an electronic device by performing at least the following: receiving, at an output stage circuit of an amplifier, an input signal from a previous stage circuit of the amplifier, driving a first subset of output transistors within the output stage circuit with an auxiliary buffer circuit to generate a first half cycle of an output signal Vout, driving a second subset of output transistors within the output stage circuit with the input signal to generate the first half cycle of the output signal Vout, and driving a set of output transistors with the input signal to generate a second half cycle of the output signal Vout, wherein the auxiliary buffer circuit equalizes the overall current gain associated with the first and second subset of output transistors with the overall current gain associated with the set of output transistors.