Low-Noise Input Amplifier Circuit With Transfer Function Linearization
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Solution Overview
Problem
Existing amplifier circuits face challenges in achieving low noise figure and high linearity while maintaining sufficient gain, often resulting in power consumption that deteriorates noise figure and limited gain improvement due to resistor contributions to input resistance.
Innovation Solution
A circuit arrangement combining emitter and base circuits with parallel configuration, utilizing resistors and transistor currents to achieve hyperbolic tangent function linearization over a wide input voltage range, replacing resistors with field effect transistors for improved performance, and optimizing resistances and currents to minimize non-linear components in output currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resistors are used to implement defined input resistance, then input resistance matching is achieved, but noise figure deteriorates and linearity is limited
Solution Approach 1:
The patent changes the physical state and type of components from resistive elements to active transistor-based negative impedance converters. By using NIC circuits with operational amplifiers and transistors, the input resistance is synthesized through active circuitry rather than passive resistors, fundamentally changing the parameter implementation from resistive to active control, thereby eliminating thermal noise while maintaining impedance matching
Solution Approach 2:
The patent substitutes passive resistive mechanisms with active electronic control mechanisms. Instead of using physical resistors that inherently generate thermal noise, the invention employs operational amplifiers and transistors configured as negative impedance converters to synthesize the desired input resistance, replacing the mechanical/resistive system with an active electronic control system that does not suffer from thermal noise limitations
2Reliability
If current is increased to improve linearity, then transistor transfer function linearization improves, but power consumption increases and noise figure deteriorates
Solution Approach 1:
The patent employs negative feedback through NIC circuits that continuously monitor and adjust the amplifier output to linearize the transistor transfer function. The feedback mechanism compensates for non-linearities without requiring excessive bias currents, using control signals to actively correct distortion while maintaining low power consumption and preserving noise figure performance
Solution Approach 2:
The patent implements dynamic control of the amplifier operating point through active feedback circuits that adapt to signal conditions. Rather than using fixed high bias currents for linearization, the circuit dynamically adjusts transistor operating parameters through feedback control, achieving linearization only when and where needed, thereby minimizing power consumption while maintaining linearity
3Productivity
If feedback operational amplifiers are used, then gain and bandwidth are improved, but stability deteriorates due to oscillation and non-linear behavior at high frequencies
Solution Approach 1:
The patent segments the feedback path into multiple controlled stages using discrete operational amplifiers and transistor pairs configured as NIC circuits. This segmentation allows independent optimization of each stage's stability characteristics while achieving overall high gain, preventing the oscillation issues that arise in single-stage high-gain feedback amplifiers by breaking the feedback loop into manageable, stable segments
Solution Approach 2:
The patent creates a composite circuit architecture combining operational amplifiers with transistor-based negative impedance converter stages. This composite structure integrates the high gain capability of op-amps with the frequency stability and linearity of transistor circuits, achieving both high productivity and stability by merging complementary circuit topologies with different strengths
Data Source
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AI summary
The invention relates to a circuit arrangement (30, 40, 70, 80, 90) of a low-noise linear input amplifier comprising a parallel connection of a common-base connection (20) and a common-emitter connection (30), wherein the emitters of two first transistors (Q3, Q4) are coupled to one another and the bases of two second transistors (Q1, Q2) are coupled to one another, the collectors are connected in parallel with the output and the source voltage (VG) is coupled to the emitters of the second transistors (Q1, Q2) and to the bases of the first transistors (Q3, Q4), wherein a linearization of the output current (OUTLNA 1, 2) as a function of the source voltage (VG) is achieved by a linearization of the transfer function, such as hyperbolic tangent function, for example, of the first and second transistors (Q1, Q2, Q3, Q4).