Digitally Controlled VGA Topology for Linear Gain and Impedance Matching

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Solution Overview

Problem

Existing digitally controlled variable gain amplifiers suffer from non-linear voltage gain due to finite input and output impedances, leading to integral non-linearity errors and increased circuit losses, footprint, and mismatches, especially in cost-sensitive applications like phased array chips.

Innovation Solution

A digitally controlled variable gain amplifier design that includes a positive amplification stage and a corresponding negative amplification stage, both equally weighted and coupled in parallel, with digital codes controlling the stages through an inverter to maintain equal on/off amplifier counts, and an auxiliary stage for even output levels, eliminating the need for dummy amplifiers and additional losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If dummy amplifiers are added to equalize impedance, then input/output impedance matching is improved, but circuit losses and footprint increase

Engineering Contradiction:

Improveimpedance matchingVSAvoidcircuit losses

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent inverts the conventional approach by using negative amplifiers that produce inverted output signals instead of dummy amplifiers. The negative amplification stage generates signals with opposite polarity that cancel out the impedance variations caused by the positive amplification stage, achieving impedance equalization without requiring additional dummy components that would increase losses and footprint.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the gain parameter to negative values by introducing amplifiers with negative amplification factors. This allows the system to dynamically adjust the total amplification weight by combining positive and negative contributions, thereby equalizing the effective impedance seen by the input and output across different digital codes without adding passive lossy components.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If more amplifiers are stacked to increase gain resolution, then voltage gain precision is improved, but device complexity and footprint increase

Engineering Contradiction:

Improvevoltage gain precisionVSAvoidcircuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent uses negative amplifiers to subtract from the total gain instead of always adding positive amplifiers. This allows achieving fine gain resolution by canceling portions of larger amplifier outputs, effectively providing higher precision gain control with fewer physical amplifier stages compared to traditional binary-weighted positive-only approaches.

Inventive Principle:

Principle #13The other way round (Inversion)

3Stability of the object's composition

If passive components are added for impedance equalization, then impedance stability is improved, but manufacturing cost and losses increase

Engineering Contradiction:

Improveimpedance stabilityVSAvoidmanufacturing cost

Core Design Contradiction:

Stability of the object's compositionVSEase of manufacture

Solution Approach 1:

The patent replaces passive mechanical/electrical components (resistors, capacitors) with active electronic components (negative amplifiers) that dynamically adjust impedance characteristics through electronic control. This substitution eliminates the need for precision-matched passive components, reducing manufacturing complexity and cost while maintaining impedance stability across process variations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentEP3823163B1A digitally controlled variable gain amplifier

Publication Date: 2025.09.24 INTERUNIVERSITAIR MICRO ELECTRONICS CENT (IMEC VZW)

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Figure 1C~1F

AI summary

A digitally controlled variable gain amplifier (1) or digitally controlled VGA (1) for generating amplification output levels (10), comprising: - a positive amplification stage (100) comprising at least two positive amplifiers (101;102); - a corresponding negative amplification stage (200) coupled to said positive amplification stage (100), wherein said corresponding negative amplification stage (200) comprises at least two negative amplifiers (201; 202); wherein said positive amplification stage (100) and said corresponding negative amplification stage (200) are digitally controlled by one or more digital codes (240); and wherein: - said corresponding negative amplification stage (200) is coupled in parallel with said positive amplification stage (100) and is equally weighted as said positive amplification stage (100); and - both said positive amplification stage (100) and said corresponding negative amplification stage (200) selectively contribute to the generation of said amplification output levels (10) for said digitally controlled VGA (1).