Bipolar Time-to-Digital Converter for Symmetric Interval Measurement

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Solution Overview

Problem

Conventional linear time-to-digital converters (TDCs) face challenges in measuring bipolar time intervals, leading to asymmetry, increased noise, and power consumption, especially in feedback systems, and are susceptible to nonlinear characteristics due to unknown delay offsets caused by imperfections and environmental variations.

Innovation Solution

A bipolar time-to-digital converter (BTDC) arrangement using a single conventional linear TDC with logic functions and an auxiliary TDC to determine polarity, along with calibration components to compensate for delay offsets, allowing for symmetric measurement of both positive and negative time intervals and reducing noise and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a positive offset is added to the signed time interval to ensure positive measurement, then the time interval can always be measured as positive, but the measurement time is prolonged resulting in increased phase noise and power consumption

Engineering Contradiction:

Improvemeasurement reliabilityVSAvoidphase noise

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The invention divides the bipolar time interval measurement into two separate unipolar measurements using two TDCs. One TDC measures the time interval when the first signal leads, and the other TDC measures the time interval when the second signal leads. This segmentation allows each TDC to operate in its optimal unipolar mode without requiring a positive offset, thereby reducing phase noise while maintaining measurement reliability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of adding a positive offset to convert bipolar measurement to unipolar measurement, the invention inverts the approach by using two unipolar TDCs that can directly handle bipolar intervals through selective operation. Each TDC is activated based on which signal leads, effectively inverting the conventional approach of offset addition and achieving noise-free bipolar measurement.

Inventive Principle:

Principle #13The other way round (Inversion)

2Ease of manufacture

If a positive offset is added to the signed time interval, then the measurement can be performed with a conventional TDC, but the conversion time increases resulting in higher power consumption

Engineering Contradiction:

ImproveTDC implementationVSAvoidpower consumption

Core Design Contradiction:

Ease of manufactureVSUse of energy by moving object

Solution Approach 1:

The invention segments the measurement function into two parallel unipolar TDC paths. Each TDC is designed for optimal unipolar operation without offset requirements, enabling efficient implementation while reducing the measurement time and power consumption compared to a single TDC with offset addition.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically selects which TDC to activate based on the relative timing of the input signals. When the first signal leads, the first TDC is activated; when the second signal leads, the second TDC is activated. This dynamic selection eliminates the need for fixed offset addition and reduces average power consumption by keeping only one TDC active at a time.

Inventive Principle:

Principle #15Dynamics

3Adaptability or versatility

If an edge selector is used with the linear TDC to determine the sign of the time interval, then bipolar measurement capability is achieved, but the device complexity increases

Engineering Contradiction:

Improvebipolar measurement capabilityVSAvoidTDC structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The invention segments the bipolar measurement function into two separate unipolar TDCs, each handling one polarity case. This eliminates the need for complex edge selection logic and signal routing within a single TDC, as each TDC simply measures its designated unipolar interval. The overall system achieves bipolar capability through parallel segmentation rather than sequential complex control.

Inventive Principle:

Principle #1Segmentation

4Manufacturing precision

If two TDCs are used, one forward and one reverse, then the measurement time is reduced resulting in reduced phase noise, but the area and power consumption increase by a factor of two

Engineering Contradiction:

Improvephase noiseVSAvoidcircuit area

Core Design Contradiction:

Manufacturing precisionVSArea of stationary object

Solution Approach 1:

The invention uses two TDCs operating in parallel, each dedicated to measuring one polarity of time intervals. This segmentation allows both TDCs to be shorter in length since they only need to cover half the measurement range, reducing individual TDC area. The total area is optimized by eliminating the need for offset addition circuitry and long delay lines required in single-TDC bipolar designs.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS8970420B2Bipolar time-to-digital converter

Publication Date: 2015.03.03 APPLE INC

AI summary

Representative implementations of devices and techniques provide bipolar time-to-digital conversion. For example, either a positive time duration or a negative time duration may be converted to a digital representation by a linear time-to-digital converter (TDC). A set of logic functions may be applied to the input of the TDC to provide start and/or stop signals for the TDC. Further, a correction component may be applied to an input or an output of the TDC to compensate for a delay offset of the TDC.