Active Imaging Sensor Beat Frequency Detection Circuit
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Solution Overview
Problem
Active imaging systems, particularly FMCW imaging systems, face complexity in measuring the beat frequency of the heterodyne beam received by image sensor pixels, which hinders efficient depth determination and simplification of electronics.
Innovation Solution
An image sensor with a frequency comparator circuit for each pixel, a digitally controlled or voltage-controlled oscillator, and a digital register to store the control signal during frequency switching, along with a circuit for addressing and reading pixel registers, simplifies the detection and measurement of beat frequencies across all pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional beat frequency measurement circuits are used in each pixel, then measurement precision is maintained, but device complexity increases significantly
Solution Approach 1:
The patent extracts the complex frequency measurement function from individual pixel circuits and relocates it to a separate, dedicated frequency measurement circuit. Each pixel only needs to output its beat frequency signal, while the measurement and comparison operations are performed externally by the extracted frequency measurement circuit, thereby simplifying pixel internal structure while preserving measurement precision.
Solution Approach 2:
The patent introduces an intermediary frequency measurement circuit that acts as a mediator between the pixel array and the control system. This intermediary circuit receives beat frequency signals from multiple pixels, performs frequency comparison and measurement operations, and outputs measurement results, thereby eliminating the need for complex measurement circuits within each pixel.
2Measurement precision
If simplified detection circuits are used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent merges the frequency measurement functions for multiple pixels into a single shared frequency measurement circuit. This consolidated circuit processes beat frequency signals from the entire pixel array using unified measurement and comparison logic, achieving accurate frequency measurement across all pixels while avoiding the repetition of complex circuits in each pixel.
Solution Approach 2:
The frequency measurement circuit is designed as a universal module that can measure beat frequencies from any pixel in the array. The circuit performs multiple functions including signal reception, frequency comparison with reference signals, beat frequency calculation, and result output, making it a multi-functional solution that serves all pixels without requiring pixel-specific complex circuits.
3Measurement precision
If complex internal circuits are implemented in each pixel, then measurement accuracy is improved, but integration density decreases
Solution Approach 1:
The patent extracts the area-intensive frequency measurement and comparison circuits from individual pixel structures and places them in a separate dedicated circuit module. This extraction dramatically reduces the area occupied by each pixel while the external circuit maintains high measurement accuracy through its specialized design optimized for frequency analysis.
Solution Approach 2:
The patent transitions the frequency measurement function from a two-dimensional integration within each pixel to a separate spatial dimension, implementing the measurement circuit externally. This dimensional separation allows pixels to maintain minimal area while the measurement functionality is preserved in a dedicated circuit module, effectively solving the area-precision trade-off.
4Use of energy by moving object
If simplified circuits are used, then power consumption is reduced, but measurement capability is compromised
Solution Approach 1:
The patent extracts the power-intensive frequency measurement and comparison operations from individual pixel circuits and consolidates them in a separate frequency measurement circuit. This extraction reduces the active circuitry in each pixel, thereby lowering power consumption, while the dedicated external circuit maintains accurate beat frequency detection capability through its specialized measurement design.
Solution Approach 2:
The frequency measurement circuit is designed to autonomously perform frequency comparison and measurement operations without requiring complex control logic within each pixel. The circuit self-manages the measurement process by comparing received beat frequency signals with reference signals and automatically calculating frequency values, thereby reducing overall system power consumption while maintaining measurement capability.
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 configuration reduces the complexity of internal circuits, enhances integration density, and lowers power consumption while enabling efficient detection and measurement of beat frequencies, thereby improving depth mapping capabilities.
Implementation Method 1
each comprising an elementary photodetector, the sensor comprising, for each pixel, a circuit for detecting a beat frequency of a portion of a heterodyne beam received by the elementary photodetector of the pixel
Implementation Method 2
a circuit for detecting a beat frequency of a portion of a heterodyne beam received by the elementary photodetector of the pixel, the detection circuit comprising a frequency comparator comprising a first input node receiving a first periodic alternating signal of frequency equal to said beat frequency
Data Source
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AI summary
The present description relates to an image sensor comprising a plurality of pixels (Pix) each comprising an elementary photodetector (211), in which each pixel (Pix) comprises a circuit (201, 203) for detecting a beat frequency of a portion of a heterodyne beam received by the elementary photodetector (211) of the pixel, and in which, in each pixel (Pix), the detection circuit (201, 203) comprises a frequency comparator (221) comprising a first input node (E1) receiving a first periodic alternating signal (fpix) of frequency equal to said beat frequency, a second input node (E2) receiving a second alternating signal (framp) of variable frequency, and an output node (S) providing an output signal switching from a first state to a second state when the frequency of the second signal (framp) exceeds the frequency of the first signal (fpix).