Feedback Op-Amp Circuit with Variable Capacitance for Low-Noise Gain Control
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Solution Overview
Problem
Existing circuit configurations for amplifying input signals face challenges in changing circuit amplification without introducing nonlinearities and noise, particularly due to the limitations of damping elements and MOS transistors in the triode range, which affect linearity and introduce interference.
Innovation Solution
The circuit configuration employs changeable capacitance values in both the coupling and feedback paths, adjusted by specific parameters and transistors, allowing for continuous and precise amplification changes while minimizing noise through the use of capacitors, and incorporating integration elements for smoothing the amplification changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If MOS transistors in the triode range are used to implement amplification-determining resistors, then circuit amplification can be continuously changed, but linearity is reduced and interference signals increase
Solution Approach 1:
The patent changes the physical parameter from resistance to capacitance for the feedback element. By using a capacitor with variable capacitance instead of a resistor with variable resistance, the circuit achieves amplification changeability while maintaining linearity. The capacitance value is varied through switching different capacitor values in parallel, avoiding the non-linear characteristics of MOS transistors in triode mode.
2Object-affected harmful factors
If resistor elements with low resistance values are used, then noise is reduced, but it becomes extremely difficult to change resistance values with high precision during operation
Solution Approach 1:
The patent replaces the mechanical/electrical system of variable resistors with a switching system of discrete capacitors. Instead of continuously varying resistance, the circuit switches between fixed capacitor values in parallel. This substitution eliminates the difficulty of maintaining precise resistance values while keeping noise low, as capacitor switching does not introduce the same level of noise and precision issues as resistance variation.
3Adaptability or versatility
If damping elements with changeable damping are connected upstream of the amplifier, then circuit amplification can be changed, but nonlinearities occur that affect circuit amplification
Solution Approach 1:
The patent extracts the amplification control function from the damping element position and relocates it to the feedback path. By placing the variable capacitance element directly in the feedback path, the control of amplification is separated from the input damping stage. This extraction eliminates the nonlinearities that would otherwise be introduced by changeable damping elements at the input, while still achieving amplification variability through feedback modification.
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 approach enables easy and reliable adjustment of circuit amplification with improved linearity and reduced noise, allowing for a range of amplification from 0 dB to 12 dB with minimal quantization error, effectively addressing the limitations of previous technologies.
Implementation Method 1
the coupling path comprises a coupling capacitor having changeable capacitance value, referred to in the following as Cb, and the feedback path comprises a feedback capacitor having changeable capacitance value, referred to in the following as C
Data Source
AI summary
The present invention relates to a circuit configuration (10) having a feedback operational amplifier (AMP) for amplifying an input signal (Vin) input into the circuit arrangement (10) and outputting the amplified input signal as an output signal (Vout). In order to be able to change the circuit amplification (Vout/Vin) easily and reliably in the circuit configuration (10) and simultaneously keep an impairment of the output signal (Vout) caused by noise relatively low, capacitance values (Cb, C) of the coupling path (12) and of the feedback path (14) are adjusted simultaneously to one another correlated in a special way.