Variable Gain Amplifier With Constant Input Impedance
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Solution Overview
Problem
Existing variable gain amplifiers face challenges in reducing noise and maintaining constant input impedance while varying gain, often leading to increased distortion and instability.
Innovation Solution
The proposed variable gain amplifier employs a resistive switching network with field effect transistors to adjust gain levels, maintaining constant input impedance and minimizing distortion by configuring switches' voltage drives to follow the input common mode level, thereby reducing noise and optimizing gain variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switchable resistor segments are used to adjust gain levels, then gain variability is improved, but input impedance constancy deteriorates
Solution Approach 1:
The feedback path is divided into multiple parallel resistor segments (first feedback resistor segment, second feedback resistor segment, third feedback resistor segment) that can be independently switched. This segmentation allows selective activation of specific resistor portions to achieve different gain levels while maintaining a more stable overall input impedance compared to using a single large variable resistor.
Solution Approach 2:
The patent changes the resistance parameter in discrete steps by switching between different feedback resistor segments. Each segment represents a specific resistance value, and by combining different segments in parallel or series configurations, the feedback impedance is adjusted in controlled increments, thereby varying gain while limiting input impedance variation.
2Adaptability or versatility
If traditional switching networks are used to vary gain, then gain adjustment capability is improved, but noise performance deteriorates
Solution Approach 1:
The patent introduces virtual ground nodes as intermediary points in the switching network. By routing switchable resistor segments through these virtual ground nodes rather than directly connecting them between signal paths, the switching action occurs at virtual ground potential, minimizing signal disturbance and reducing switching noise and distortion that would otherwise be injected into the signal path.
Solution Approach 2:
The switching network is designed to operate at virtual ground potential, creating an equipotential environment for the switching nodes. This ensures that when switches transition between states, there is minimal voltage difference across the switching elements, thereby reducing switching transients, noise, and distortion while still achieving the desired gain adjustment.
3Adaptability or versatility
If gain is varied using conventional methods, then adaptability is improved, but distortion increases
Solution Approach 1:
Virtual ground nodes serve as intermediary connection points for the switchable resistor segments in both the input and feedback paths. This intermediary structure allows gain adjustment through resistance changes while keeping the switching nodes at virtual ground potential, thereby minimizing signal distortion that would result from direct switching in the signal path.
Solution Approach 2:
By maintaining switching nodes at virtual ground potential through the equipotential design, the patent minimizes voltage variations during switching transitions. This reduces the generation of distortion components while still enabling effective gain control through the selective activation of different resistor segments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively decreases output noise while adjusting gain, maintains constant input impedance, and minimizes distortion, enhancing the amplifier's operational stability and performance.
Implementation Method 1
The switchable input resistor segment includes an input resistor, a first input switch, and a second input switch, wherein the input resistor is coupled with the input terminal, the first virtual ground node via the first input switch, and the second virtual ground node via the second input switch. The switchable feedback resistor segment includes a feedback resistor and a feedback switch, wherein the feedback resistor is coupled with the output terminal and the first virtual ground node via the feedback switch. The first input switch, the second input switch, and the feedback switch can be field effect transistors.
Data Source
AI summary
The present disclosure provides an amplifier and associated methods of operations. An exemplary amplifier an input terminal; an output terminal; a first virtual ground node; a second virtual ground node; an operational amplifier coupled with the input terminal and the output terminal; a resistive input section coupled with an input of the operational amplifier; and a resistive feedback section coupled with an output of the operational amplifier. The resistive input section includes a fixed input resistor coupled with the input terminal and the first virtual ground node, and a switchable input resistor segment coupled with the fixed input resistor in parallel. The resistive feedback section includes a fixed feedback resistor coupled with the output terminal and the first virtual ground node, and a switchable feedback resistor segment coupled with the fixed feedback resistor in parallel.