DLL-Based Temperature Sensor One-Point Calibration
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Solution Overview
Problem
Microprocessor thermal profiling requires efficient temperature sensing to manage temperature variations, but existing delay-based CMOS smart temperature sensors necessitate two-point calibration, which is resource-intensive and complex, especially in microprocessor applications where simplicity is crucial.
Innovation Solution
A delay-based smart temperature sensor employing a one-point calibration method, utilizing a delay-locked loop (DLL) as a time-to-digital converter (TDC) to separate inverter delay into temperature-dependent and process-dependent functions, allowing for calibration in a single step and using a stable clock source for accurate temperature measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two-point calibration is used to compensate for process variation, then measurement precision is improved, but device complexity increases due to additional temperature control steps
Solution Approach 1:
The patent extracts the process variation component from the temperature measurement by using a reference inverter chain that is isolated from temperature variations. By measuring only the delay difference between the test inverter chain and the reference chain, the calibration process eliminates process variations without requiring two-point calibration, thus reducing calibration complexity while maintaining measurement precision
Solution Approach 2:
The patent introduces a reference inverter chain as an intermediary element that experiences the same process variations but is isolated from temperature variations. This reference chain serves as a mediator to cancel out process effects, allowing single-point calibration to achieve the same precision as two-point calibration would provide
2Ease of manufacture
If delay-based CMOS temperature sensors are used, then ease of manufacture is improved by using standard CMOS transistors, but measurement precision deteriorates compared to bandgap-based sensors
Solution Approach 1:
The patent implements a feedback mechanism where the measured delay difference is used to calculate and output a temperature value. By continuously measuring the delay difference between the test and reference inverter chains and converting this measurement to a temperature reading through calibration data, the system achieves measurement precision comparable to bandgap-based sensors while maintaining the manufacturing simplicity of standard CMOS transistors
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
The one-point calibration approach simplifies the calibration process, reduces system test effort, and provides consistent temperature representation across different process corners with minimal error, making it suitable for microprocessor applications.
Implementation Method 1
Exploiting the fact that the time delay of a CMOS inverter varies with temperature, the CMOS smart temperature sensors measure delays in open-loop inverter chains
Implementation Method 2
Although the DLL requires an external stable frequency reference like a crystal oscillator, such stable clock sources are readily available in almost all microprocessor applications
Data Source
AI summary
A temperature sensor includes an open-loop delay line comprising plural delay cells and a multiplexer configured to select a first number of the plural delay cells; a delay-locked loop comprising plural delay cells and a multiplexer configured to select a second number of the plural delay cells; a clock coupled to an input of the open-loop delay line and to an input of the delay-locked loop; a detector having a first input coupled to an output of the open-loop delay line and a second input coupled to an output of the delay-locked loop; and a finite state machine configured to detect a transition in the output of the phase detector.