Input Resistance Gain Control for dB-Linear Analog Amplifiers
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Solution Overview
Problem
Existing dB-linear gain control circuits in analog signal processing systems require adjustment of negative feedback devices, which alters signal processing characteristics and complicates integration and miniaturization, especially when combined with other analog signal processing units.
Innovation Solution
A gain control device that adjusts only the input terminal resistance, using a combination of fixed and variable resistors to achieve dB-linear gain control without affecting the negative feedback device connected to the operational amplifier, allowing for separate control of gain without altering signal processing characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If negative feedback device resistance is adjusted to achieve dB-linear gain control, then gain control is achieved, but signal processing characteristics are altered
Solution Approach 1:
The patent separates gain control function from signal processing function by using distinct circuit paths. The negative feedback device is dedicated to signal processing while a separate input terminal resistance unit handles gain control, allowing independent optimization of both functions without mutual interference
Solution Approach 2:
The patent introduces an intermediary input terminal resistance unit that acts as a mediator between the input signal and the signal processing unit. This intermediary component enables gain control without directly affecting the negative feedback device or the core signal processing characteristics
2Ease of operation
If negative feedback device resistance is adjusted for gain control, then gain varies, but integration with analog signal processing units becomes complex
Solution Approach 1:
The patent divides the amplifier into functionally independent modules: a signal processing unit with fixed negative feedback device and a separate gain control unit with variable input terminal resistance. This segmentation simplifies integration with analog signal processing units as the gain control function is isolated and does not interfere with the signal processing unit's characteristics
Solution Approach 2:
The negative feedback device serves exclusively for signal processing without being involved in gain control, making it universally applicable to various analog signal processing units. The gain control function is achieved through the variable input terminal resistance unit, which can be independently configured without affecting the universality of the signal processing unit
3Ease of operation
If additional gain control circuit is added to the front end, then dB-linear gain control is achieved, but circuit volume increases
Solution Approach 1:
The patent merges the gain control function with the existing input terminal of the amplifier rather than adding a separate front-end circuit. The variable resistance unit is integrated at the input terminal, combining signal input and gain control functions in a compact arrangement that avoids increasing overall circuit volume
Solution Approach 2:
The input terminal is designed to serve multiple functions: signal input and gain control. By making the input terminal multi-functional with an integrated variable resistance unit, the patent eliminates the need for additional dedicated gain control circuits, thereby reducing circuit volume while maintaining dB-linear gain control capability
4Ease of operation
If additional gain control circuit is added, then gain control capability is improved, but power consumption increases
Solution Approach 1:
The patent combines gain control with the existing input terminal circuitry rather than adding a separate power-consuming gain control circuit. The variable resistance unit at the input terminal reuses existing circuit resources, minimizing additional power consumption while providing full gain control capability
Solution Approach 2:
The input terminal unit is designed to perform both signal input and gain control functions universally. This multi-functionality eliminates the need for separate gain control circuitry that would consume additional power, as the same input terminal structure serves dual purposes with minimal additional power requirements
Data Source
AI summary
Provided are a gain control device and an amplifier using the gain control device. The gain control device includes a first input resistance unit having a first variable resistor whose resistance is linearly variable and a first fixed resistor respectively receiving a first input signal and a second input signal having a sign different from the first input signal and outputting current through a first output terminal, and a second input resistance unit having a second fixed resistor and a second variable resistor whose resistance is linearly variable respectively receiving the first input signal and the second input signal and outputting current through a second output terminal.Since the gain control device can separately perform dB-linear gain control, it is easily combined with a circuit, such as a continuous-time sigma-delta modulator (SDM), a continuous-time filter, and a continuous-time analog-to-digital converter (ADC), and enables miniaturization and low power consumption.