Current-to-Time TDC Sensing for Scalable Crossbar Arrays

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Solution Overview

Problem

The scaling of analogue-to-digital converters (ADCs) in parallel computing systems, particularly in AI processors, is hindered by power consumption and area demands, which limits the scalability of sense circuits in applications like crossbar neural networks.

Innovation Solution

The implementation of time-to-digital converter (TDC)-based devices, comprising a crossbar array, current-controlled delay line, and TDC circuit, which directly convert current to time pulses for digital output, reducing power consumption and latency, and are suitable for crossbar Memristor, Memtransistor, or FeCAP/FeFET-based computing and storage arrays.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If ADC circuits are used for current-to-digital conversion in parallel computing systems, then measurement precision is achieved, but power consumption and area increase, limiting scalability

Engineering Contradiction:

Improvecurrent-to-digital conversion precisionVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent changes the conversion domain from voltage-based ADC to time-based TDC. By converting current to time pulses through exponential charging/discharging of capacitors, the system achieves precise measurement while consuming significantly less power, as time-domain conversion requires simpler circuitry without the complex reference voltages and comparators needed in ADC

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional voltage-based conversion mechanism (ADC) with a time-based mechanism (TDC). The exponential charging curve of capacitors through current sources creates time pulses that encode current values, substituting complex voltage comparison with simpler time measurement that consumes less power

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If ADC circuits are used for current-to-digital conversion in parallel computing systems, then measurement precision is achieved, but device area increases, limiting scalability

Engineering Contradiction:

Improvecurrent-to-digital conversion precisionVSAvoidcircuit area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent transitions from voltage-domain measurement (ADC requiring large reference voltage circuits, comparators, and DACs) to time-domain measurement (TDC requiring only capacitors, current sources, and time counters). This parameter change dramatically reduces the area footprint while maintaining measurement precision through time-based encoding

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent extracts and eliminates the complex voltage reference generation circuitry, precision comparators, and digital-to-analog converters that are essential components of ADC but consume significant area. The time-based approach uses only simple capacitive charging circuits and time counters, removing unnecessary components

Inventive Principle:

Principle #2Taking out (Extraction)

3Productivity

If multiple parallel branches with ADC are implemented, then computing capability increases, but power consumption and area demand prevent scaling

Engineering Contradiction:

Improveparallel computing capabilityVSAvoidtotal power consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The patent segments the conversion function into independent time-based units that can be parallelized. Each parallel branch uses simple capacitor charging circuits instead of complex ADC, allowing numerous parallel branches to be implemented with linearly increasing power consumption rather than exponentially increasing consumption as would be required with ADC

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

By changing from voltage-based to time-based conversion, the patent enables efficient parallelization. Time pulses from multiple parallel branches can be multiplexed and measured sequentially by a single TDC unit, allowing high parallel computing capability with shared measurement resources, thereby reducing total power consumption

Inventive Principle:

Principle #35Parameter changes

4Measurement precision

If ADC circuits are used, then current-to-digital conversion is achieved, but latency increases due to complex conversion process

Engineering Contradiction:

Improveconversion accuracyVSAvoidconversion latency

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

Instead of converting current to voltage and then to digital (the conventional ADC approach requiring multiple stages), the patent inverts the approach by directly converting current to time pulses through capacitor charging. This single-step time-domain conversion eliminates intermediate voltage conversion stages, reducing latency while maintaining precision through the exponential charging relationship

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS12517467B2Time-to-digital converter-based device

Publication Date: 2026.01.06 NATIONAL UNIVERSITY OF SINGAPORE

AI summary

Disclosed is a time-to-digital converter (TDC)-based device comprising a crossbar array for generating a current, a current-controlled delay line 104 for converting the current received from the crossbar array into a time pulse, and a TDC circuit 106 for measuring and converting the time pulse into digital output.