Linear Amplifier Tail Current Control for Wideband Linearity
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Solution Overview
Problem
Existing linear amplifiers face challenges in achieving high linearity and wide frequency bands while maintaining large signal strength, as they require transistors with high withstand voltage, which often results in a trade-off between withstand voltage performance and maximum operating frequency.
Innovation Solution
A linear amplifier configuration that includes a pre-amplifier, a post-amplifier, an amplitude detector, and a comparator to control the tail current of the pre-amplifier, allowing the output voltage to be maintained at a constant reference voltage, thereby reducing the need for high withstand voltage transistors and achieving high linearity and wide frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If transistors with high withstand voltage are used to enable large signal output, then the signal strength can be increased, but the maximum operating frequency performance deteriorates due to the trade-off relationship between withstand voltage and operating frequency
Solution Approach 1:
The patent applies dynamic control to the tail current source, making it adjustable based on operating conditions. The tail current is dynamically reduced when the output signal amplitude exceeds a reference level, allowing the amplifier to operate at higher frequencies without requiring high-withstand-voltage transistors. This dynamic adaptation resolves the contradiction between signal strength and operating frequency by adjusting the current level according to the signal amplitude.
Solution Approach 2:
The patent changes the operating parameters of the amplifier by introducing amplitude-dependent tail current control. When the output signal amplitude exceeds the reference voltage, the tail current is reduced to a lower level, effectively changing the operating point of the amplifier. This parameter change allows the use of transistors with lower withstand voltage ratings while maintaining high-frequency performance, thus resolving the contradiction between signal strength and operating frequency.
2Reliability
If the output signal amplitude is reduced to maintain high linearity, then the linearity is improved, but the signal strength decreases
Solution Approach 1:
The patent uses dynamic tail current control to maintain linearity while preserving signal strength capability. By reducing the tail current only when the output amplitude exceeds the reference level, the amplifier maintains high linearity in the normal operating range while retaining the capability to output large signals when needed. This dynamic adjustment resolves the contradiction between linearity and signal strength.
Solution Approach 2:
The patent implements feedback control by monitoring the output signal amplitude and adjusting the tail current accordingly. The amplitude detector continuously monitors the output and feeds this information back to the tail current source, which adjusts the current level to maintain optimal linearity. This feedback mechanism ensures high linearity is maintained while preserving the ability to output strong signals, resolving the contradiction between these two parameters.
Data Source
AI summary
A linear amplifier includes a pre-amplifier configured to amplify an input differential signal, a post-amplifier configured to amplify an output signal of the pre-amplifier, an amplitude detector configured to detect an amplitude of an output signal of the post-amplifier, and an output voltage corresponding to the detected amplitude, a comparator configured to control a tail current source of the pre-amplifier such that when the output voltage of the amplitude detector is less than or equal to a reference voltage, a tail current of the pre-amplifier is set to a constant value, and when the output voltage of the amplitude detector is larger than the reference voltage, the tail current is reduced to make the output voltage of the amplitude detector equal to the reference voltage.