Differential Linear Amplifier Feedback for Wideband Constant Gain
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Solution Overview
Problem
Existing linear amplifiers fail to provide high linearity and constant gain over a wide band, particularly in applications like USB3.1 Gen2 and USB4, leading to waveform distortion and signal loss.
Innovation Solution
The linear amplifier design incorporates a signal processing circuit with specific transistors, resistors, capacitors, and a differential amplifier for common mode feedback, allowing for high linearity and constant gain across a wide frequency range by controlling the base voltage and maintaining low frequency component transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional linear amplifier circuits are used, then the circuit structure is simple, but the linearity and gain constancy over wide band are insufficient
Solution Approach 1:
The patent implements common mode feedback by detecting the common mode voltage at the output and feeding it back to the bases of the input transistors through feedback resistors. This feedback mechanism automatically adjusts the operating point to maintain constant gain and high linearity across the wide frequency band from 100 Hz to 20 Gbps, directly resolving the technical contradiction between performance and complexity.
Solution Approach 2:
The patent changes the operating parameters of the transistor circuit by introducing capacitors in parallel with feedback resistors and adjusting the feedback network configuration. These parameter changes enable the circuit to maintain optimal linearity and gain constancy characteristics across the entire wide frequency range while managing the circuit complexity through systematic parameter optimization.
2Manufacturing precision
If high linearity is achieved through conventional means, then waveform distortion is reduced, but gain constancy over wide band deteriorates
Solution Approach 1:
The patent introduces dynamic elements (capacitors) into the feedback network to create frequency-dependent feedback paths. The capacitors C1 and C2 in parallel with feedback resistors R1 and R2 create different feedback characteristics at different frequencies, enabling the circuit to maintain both high linearity at low frequencies and constant gain at high frequencies up to 20 Gbps, thus resolving the contradiction between linearity and wide-band gain constancy.
Solution Approach 2:
The patent adds the frequency dimension to the feedback mechanism by introducing capacitive elements that create different feedback paths for different frequency ranges. This multi-dimensional approach allows simultaneous optimization of linearity (dominant at lower frequencies) and gain constancy (critical at higher frequencies), enabling the circuit to satisfy both requirements across the entire 100 Hz to 20 Gbps bandwidth.
Data Source
AI summary
A linear amplifier outputs differential signals corresponding to differential signals input to a first signal input terminal and a second signal input terminal, and includes a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a second capacitor, a third transistor, a fourth transistor, a differential amplifier, and a signal processing circuit. The signal processing circuit includes a first transistor and a second transistor, and includes a resistor as a common voltage output part that outputs a common voltage. The differential amplifier receives the common voltage and a reference voltage, and applies a voltage corresponding to the voltage difference between the common voltage and the reference voltage to the control terminals of the transistors.