Signal-Dependent Class AB Amplifier Biasing for Linearity
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Solution Overview
Problem
Existing amplifying circuits face a trade-off between achieving high linearity and low power consumption, as optimizing one aspect typically compromises the other, due to the fixed operational point determined by the class A input stage circuit.
Innovation Solution
The proposed amplifying circuit employs a class AB input stage and output stage with a feed-forward biasing mechanism, where the voltage difference between biasing signals changes based on the input signal, allowing for optimized linearity during signal amplification and reduced power consumption when no signal is present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the static current Iq is set to a smaller value to reduce power consumption, then power consumption is reduced, but the voltage difference VAB between gate voltages of transistors M25 and M26 becomes larger, making the linearity of the output stage worse and the maximum swing of the output signal smaller
Solution Approach 1:
The patent applies dynamics by making the biasing voltages VAB dynamically adjustable based on the input signal amplitude. When the input signal is zero or small, VAB is set to a larger value to reduce power consumption. When the input signal amplitude increases, VAB is automatically adjusted to a smaller value to improve linearity and maximize output signal swing. This dynamic adjustment resolves the contradiction between power consumption and linearity.
Solution Approach 2:
The patent changes the parameter VAB (voltage difference between gate voltages of output stage transistors) from a fixed value to a variable value that depends on the input signal characteristics. By changing this parameter dynamically, the circuit can optimize both power consumption and linearity at different operating conditions, resolving the technical contradiction.
2Manufacturing precision
If the voltage difference VAB between gate voltages of transistors M25 and M26 is increased to improve linearity and maximum swing, then linearity and signal swing are improved, but the static current Iq increases, leading to higher power consumption
Solution Approach 1:
The biasing circuit dynamically adjusts VAB based on the input signal amplitude. When input signal is present and large, VAB is reduced to improve linearity. When input signal is absent or small, VAB is increased to reduce power consumption. This dynamic behavior resolves the contradiction between linearity and power consumption.
Solution Approach 2:
The parameter VAB is changed from a constant value to a signal-dependent variable. The biasing circuit modifies VAB according to the input signal characteristics, allowing the circuit to achieve good linearity when needed while minimizing power consumption when the input signal is small or zero.
3Stability of the object's composition
If the operational point is fixed by the class A input stage circuit to ensure stable operation, then operational stability is maintained, but the circuit cannot simultaneously achieve optimized signal amplifying qualities and power consumption
Solution Approach 1:
The patent introduces dynamic adjustment of the operational point through the biasing circuit that responds to input signal amplitude. The operational point is no longer fixed but adapts dynamically based on signal conditions, allowing the circuit to maintain stability while achieving optimization of both signal amplifying qualities and power consumption.
Solution Approach 2:
The biasing circuit uses feedback from the input signal to automatically adjust the biasing voltages. This feedback mechanism allows the circuit to maintain stable operation while adapting the operational point to optimize performance for different signal conditions, resolving the contradiction between stability and adaptability.
Data Source
AI summary
An amplifier includes: a class AB input stage, receiving an input signal, for generating an inner signal according to the input signal; class AB output stage, includes: a biasing circuit, for providing a first voltage and a second voltage according to the inner signal; and an output stage, for generating an output signal according to the first voltage and the second voltage; wherein a voltage difference between the first voltage and the second voltage generated by the biasing circuit is corresponding to the input signal.