Matched Feedback Amplifier Using Feed-Forward Distortion Compensation
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Solution Overview
Problem
Conventional differential feedback amplifiers face issues with high power consumption, narrow dynamic range, low linearity, and mismatched input and output impedances, which are exacerbated by attempts to compensate for these problems.
Innovation Solution
A low noise, impedance-matched amplifier is achieved using a feed-forward linearization technique with negative feedback and distortion compensation, eliminating active tail current sources and employing emitter degeneration components, which provides low power requirements and high linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional differential feedback amplifiers use active tail current sources and compensation amplifiers to improve linearity, then distortion is reduced, but power consumption increases
Solution Approach 1:
The patent removes active tail current sources from both the main amplifier and compensation amplifier, extracting the power-consuming elements while maintaining linearity through alternative biasing schemes using passive components and feedback networks
Solution Approach 2:
The patent employs multiple feedback paths including emitter feedback resistors and collector feedback networks to maintain linearity and distortion compensation without requiring active tail current sources, using feedback to replace the function of the removed active biasing elements
2Reliability
If input resistors are added to compensation amplifier bases to compensate for capacitance differences, then high-frequency linearity is improved, but the amplifier complexity increases
Solution Approach 1:
The patent applies different resistance values to different compensation amplifier bases (RB1 ≠ RB2) to locally compensate for specific capacitance differences in each transistor, tailoring the compensation to the actual device variations rather than using a uniform approach
Solution Approach 2:
The patent modifies the resistance parameters at the compensation amplifier bases to counteract the capacitive effects, changing the electrical parameters to achieve frequency-independent linearity compensation
3Reliability
If main amplifier and compensation amplifier use different transistor characteristics to achieve distortion subtraction, then linearity is improved, but impedance matching becomes more difficult
Solution Approach 1:
The patent creates a simplified copy of the main amplifier's distortion characteristics in the compensation amplifier, using proportionally scaled transistors and passive components to replicate the distortion pattern that can then be subtracted, rather than requiring exact transistor matching
Solution Approach 2:
The patent systematically adjusts the parameters of compensation amplifier components (transistor sizes, resistor values, capacitor values) to achieve both distortion compensation and impedance matching simultaneously through coordinated parameter optimization
4Reliability
If load resistors are used in main amplifier and input resistors in compensation amplifier, then distortion compensation is achieved, but additional impedance matching circuitry is required
Solution Approach 1:
The patent designs the compensation amplifier to serve multiple functions simultaneously: distortion generation, impedance transformation, and output buffering, eliminating the need for separate impedance matching circuits by making the compensation stage multi-functional
Solution Approach 2:
The patent merges the impedance matching function with the distortion compensation function by having the compensation amplifier's output stage also serve as the impedance transformation network, combining what would traditionally be separate functional blocks
Data Source
AI summary
An impedance-matched amplifier utilizing a feed-forward linearization technique involving multiple negative feedbacks and distortion compensation without active tail current sources reduces noise, distortion, power consumption and heat dissipation requirements and increases linearity, dynamic range, signal-to-noise-ratio, sensitivity and quality of service. Some differential amplifier embodiments of the invention consume less than 2 mA at 5 Volts or 10 mW power consumption per 1 mW in peak and sustained output IP3 performance above 40 dBm. In contrast, for an input signal frequency of 200 MHz, a 16 dB gain state-of-the-art differential amplifier consumes 100 mA at 5 Volts with a peak output IP3 of 36 dBm while an implementation of a 16 dB gain differential amplifier embodying the invention consumes 77.7 mA at 5 Volts with a peak output IP3 of 46 dBm and sustained at or above 40 dBm over a wide frequency range.