Current-Mode Programmable Gain Amplifier for Low-Noise Gain Control

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Solution Overview

Problem

Conventional programmable gain amplifiers inefficiently block noises, leading to a decrease in signal-to-noise ratio (SNR) due to noise amplification during signal amplification.

Innovation Solution

A programmable gain amplifier design incorporating an active load module, two differential pairs, and a power source module, which forms a feedback loop and adjusts current potentials to control equivalent gain, eliminating the need for physical resistors and thereby reducing noise amplification.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If conventional programmable gain amplifiers use operational amplifiers and resistors to amplify signals, then the signal amplification function is achieved, but noise is also amplified leading to decreased signal-to-noise ratio

Engineering Contradiction:

Improvesignal amplification capabilityVSAvoidnoise amplification

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the conventional operational amplifier and resistor-based amplification system with a current-mode differential pair circuit system. This substitution eliminates the need for physical resistors and uses controlled current sources to achieve signal amplification, thereby reducing thermal noise and other harmful effects associated with conventional resistor-based designs.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the fundamental operating parameters of the amplifier by transitioning from voltage-mode operation (using operational amplifiers) to current-mode operation (using differential pairs with controlled current sources). This parameter change allows for better noise performance while maintaining signal amplification capability, as current-mode circuits inherently provide lower noise levels.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If physical resistors are used in the amplifier circuit to control gain, then the gain control function is achieved, but noise is introduced and amplified

Engineering Contradiction:

Improvegain control capabilityVSAvoidnoise introduction

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent substitutes physical resistors with electronically controlled current sources in the differential pair configuration. This replacement enables gain control through current modulation rather than resistance variation, eliminating the thermal noise inherently generated by resistors while preserving the programmable gain functionality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces controlled current sources as intermediary elements between the input signal and the output stage. These current sources act as mediators that can be precisely controlled to achieve the desired gain without introducing the noise that would be generated by equivalent resistor-based control mechanisms.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If conventional amplifier structures are used, then the circuit design is simple, but noise blocking capability is insufficient

Engineering Contradiction:

Improvecircuit structure simplicityVSAvoidnoise blocking capability

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the simple but noisy operational amplifier structure with a differential pair-based current mode structure. While this increases circuit complexity slightly, it dramatically improves noise blocking capability by eliminating the primary noise sources present in conventional designs, achieving a favorable trade-off between complexity and performance.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS10122337B2Programmable gain amplifier

Publication Date: 2018.11.06 SILICON INTEGRATED SYSTEMS CORP

AI summary

A programmable gain amplifier includes an active load module, a first differential pair, a second differential pair and a power source module. The first and second differential pairs are electrically connected to the active load module. The power source module is electrically connected to the first current source end of the first differential pair and the second current source end of the second differential pair. The power source module supplies a first current to the first differential pair through the first current source end. The power source module supplies a second current to the second differential pair through the second current source end. The power source module adjusts the potential of the first current, the potential of the second current, or both.