Resonant RF Face Tracking Circuit With Edge Sampling

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Solution Overview

Problem

Conventional LC resonant drive circuits for face tracking in Mixed Reality (MR) devices require high power consumption and bulky inductors, which increase circuit area and cost, while also being inefficient in terms of dynamic range and resolution.

Innovation Solution

A novel resonant drive and sampling scheme that employs a driver circuit, an LC resonance circuit formed by an inductor and capacitor, and a sample and hold circuit, where the driver circuit generates a drive signal with a resonant frequency that changes with capacitance variations, and the sample and hold circuit samples the output at the falling edge of the drive signal to detect facial movements with reduced power consumption and circuit area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional LC resonant drive circuits are used to achieve sufficient dynamic range and resolution in face tracking, then measurement precision is improved, but power consumption increases and circuit area expands due to bulky inductors

Engineering Contradiction:
Improvedynamic range and resolutionVSAvoidpower consumption
Core Design Contradiction:
Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent changes the operating parameters of the resonant circuit by using a ring oscillator to generate a clock signal at a frequency that is a multiple of the resonant frequency, and by using a switched capacitor circuit to simulate the inductor function. This parameter change allows the system to achieve the required dynamic range and resolution without using bulky physical inductors, thereby reducing power consumption and circuit area while maintaining measurement precision

Inventive Principle:
Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional mechanical/physical inductor component with an electronic switched capacitor circuit controlled by a ring oscillator. This substitution eliminates the need for bulky inductors while maintaining the resonant circuit's functionality for achieving sufficient dynamic range and resolution in face tracking measurements

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If conventional LC resonant drive circuits with bulky inductors are used to achieve sufficient dynamic range and resolution, then measurement precision is improved, but device volume increases

Engineering Contradiction:
Improvedynamic range and resolutionVSAvoidcircuit area
Core Design Contradiction:
Measurement precisionVSVolume of moving object

Solution Approach 1:

The patent replaces the traditional mechanical/physical inductor component with an electronic switched capacitor circuit controlled by a ring oscillator. This substitution eliminates the need for bulky inductors while maintaining the resonant circuit's functionality for achieving sufficient dynamic range and resolution in face tracking measurements, thereby significantly reducing circuit area

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operating parameters by using a ring oscillator to generate a clock signal at a frequency that is a multiple of the resonant frequency, and by using a switched capacitor circuit to simulate the inductor function. This allows the system to achieve the required measurement precision without using bulky physical inductors, thereby reducing circuit area

Inventive Principle:
Principle #35Parameter changes

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 achieves high sensitivity in RF facial tracking with reduced circuit area and cost, maintaining high sensitivity while lowering power consumption and component size, suitable for portable MR devices.

Implementation Method 1

an LC resonance circuit formed by an inductor circuit and a capacitance from an antenna, which has a resonant frequency that changes as the capacitance of the antenna varies responsive to facial movements of the user

Methodology Applied
Scientific EffectLC Resonance: Resonance

Implementation Method 2

the resonant frequency that changes as the capacitance of the antenna varies responsive to facial movements of the user

Methodology Applied
Scientific EffectCapacitance variation: Capacitance

Data Source

PatentUS12126205B2High sensitivity resonant drive scheme for RF face tracking
Publication Date: 2024.10.22 MICROSOFT TECHNOLOGY LICENSING LLC
  • US12126205B2 patent drawing
  • US12126205B2 patent drawing
  • US12126205B2 patent drawing

AI summary

A system for facial movement detection with reduced size and reduced cost by employing a novel resonant drive and sampling scheme is disclosed. An example battery operated system includes a driver circuit, an LC resonance circuit formed by an inductor circuit and a capacitance from an antenna, and a sample and hold circuit. The driver circuit can be configured by a controller to generate a drive signal for the LC resonance circuit, which has a resonant frequency that changes as the capacitance of the antenna varies responsive to facial movements of the user. The sample and hold circuit samples the output of the LC resonance circuit responsive to a falling edge of the drive signal for the LC resonance circuit, wherein an output of the sample and hold circuit is a sampled sense signal that may be further processed to detect facial movements of the user.