Constant-Current Low-Voltage VGA for Stable Phase and Linearity

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Solution Overview

Problem

Variable gain amplifiers (VGAs) in phased array antennas suffer from increased parasitic capacitance, poor linearity performance, and significant phase variations relative to gain settings, which can lead to phase incoherence and require frequent recalibrations.

Innovation Solution

The development of low voltage VGAs with low phase sensitivity, implemented using digitally controlled VGA circuits that maintain constant current and reduce parasitic capacitance, while providing accurate gain steps and constant linearity over a gain range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional VGAs are used in phased array antennas, then gain control is provided, but parasitic capacitance increases and phase variations occur

Engineering Contradiction:

Improvegain controlVSAvoidparasitic capacitance

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the operating parameters of the VGA by using constant current biasing instead of conventional voltage control. This parameter change reduces parasitic capacitance effects while maintaining gain control functionality. The constant current source maintains a fixed operating point that minimizes capacitance variations across different gain settings.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces conventional voltage-controlled gain mechanisms with a current-controlled approach. By substituting voltage control with current control, the system achieves better linearity and reduced phase sensitivity. The current-controlled variable gain stage eliminates the need for voltage-dependent capacitance management.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If conventional VGAs are used in phased array antennas, then gain adjustment is enabled, but linearity performance deteriorates

Engineering Contradiction:

Improvegain adjustmentVSAvoidlinearity performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the control parameter from voltage to current, which fundamentally improves linearity performance. The constant current biasing ensures that the VGA operates in a linear region across all gain settings, eliminating the non-linear distortions typical of conventional voltage-controlled VGAs.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback mechanisms that monitor and correct for non-linearities in the VGA. The constant current source acts as a feedback element that maintains a stable operating point, automatically compensating for variations and ensuring consistent linearity across the gain range.

Inventive Principle:

Principle #23Feedback

3Adaptability or versatility

If conventional VGAs are used in phased array antennas, then variable gain is provided, but phase sensitivity to gain changes increases

Engineering Contradiction:

Improvevariable gainVSAvoidphase sensitivity

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent changes the control mechanism from voltage-based to current-based control, which decouples phase and gain control. The constant current biasing ensures that phase characteristics remain stable while gain is varied, significantly reducing phase sensitivity to gain changes and improving beamforming precision.

Inventive Principle:

Principle #35Parameter changes

4Measurement precision

If compensation circuits are implemented to limit phase variations, then phase stability is improved, but current consumption increases

Engineering Contradiction:

Improvephase stabilityVSAvoidcurrent consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent replaces complex compensation circuits with a simpler constant current biasing approach. By substituting the need for active phase compensation with a fundamentally different current-controlled architecture, the system achieves phase stability without the penalty of increased current consumption associated with compensation circuits.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS20250055432A1Low voltage variable gain amplifier with low phase sensitivity

Publication Date: 2025.02.13 SPACE EXPLORATION TECHNOLOGIES CORP

AI summary

Technologies are provided for variable gain amplifiers (VGAs). An example VGA includes a resistor ladder network comprising resistor legs coupled to a first plurality of resistors and a second plurality of resistors, a first set of differential switches connected to the resistor ladder network, a second set of differential switches connected to a set of output nodes, a third set of differential switches connected to the resistor ladder network, a fourth set of differential switches connected to the set of output nodes, and a fifth transistor and a sixth transistor comprising a differential pair coupled to a differential input signal. The fifth transistor is connected to the first set of differential switches and the sixth transistor connected to the third set of differential switches.