Time-to-Digital Converter BIST Using Dual-Oscillator Testing

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Solution Overview

Problem

Time-to-digital converters with asynchronous internal structures are difficult to test during production due to their inherent asynchronous nature, making it challenging to force delay lines and comparator inputs into a static state for effective testing.

Innovation Solution

Incorporating a built-in self-test (BIST) mechanism using two oscillators with slightly different frequencies to generate oscillating signals that propagate through the converter, allowing for the evaluation of output signals and detection of potential errors through histogram analysis.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a time-to-digital converter uses an asynchronous internal structure with delay lines, then measurement functionality is achieved, but testability during production deteriorates

Engineering Contradiction:

Improvemeasurement functionalityVSAvoidtestability

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent applies preliminary action by forcing the delay line into a static state before testing begins. Test signals are applied to the start input while the delay line is held static, allowing comparators to be properly initialized and tested before asynchronous operation commences. This preparatory static state enables effective production testing despite the inherently asynchronous nature of the converter.

Inventive Principle:

Principle #10Preliminary action

2Difficulty of detecting and measuring

If delay line inputs are forced into a static state for testing, then test signals can be applied, but the asynchronous operation required for normal function is disrupted

Engineering Contradiction:

Improvetest signal applicationVSAvoidasynchronous operation

Core Design Contradiction:

Difficulty of detecting and measuringVSReliability

Solution Approach 1:

The patent segments the testing process into distinct phases: a static initialization phase where the delay line is held stationary and test signals are applied to verify comparator functionality, followed by an asynchronous measurement phase where normal operation resumes. This segmentation allows both testing requirements and operational requirements to be satisfied in their respective phases without conflict.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements periodic action by alternating between static test modes and asynchronous measurement modes. During production testing, the converter periodically enters a static state for test signal application, then returns to asynchronous operation. This periodic switching between states enables both effective testing and maintained operational reliability.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS8072361B2Time-to-digital converter with built-in self test

Publication Date: 2011.12.06 APPLE INC

AI summary

Apparatuses and methods related to time-to-digital converters (TDCs) are herein described. Generally, a time-to-digital converter is a device which measures a time period or time interval and outputs a digital value representing the measured time period. In an implementation, an apparatus is provided comprising a time-to-digital converter circuit, which further comprises a built-in self test (BIST). The built-in self test may be implemented using one or more oscillators coupled to the time-to-digital converter via one or more multiplexer devices.