Ring Oscillator Temperature Sensing With Supply-Voltage Compensation
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Solution Overview
Problem
Ring-oscillator-based temperature sensors in integrated circuits are overly sensitive to power supply voltage variations, leading to inaccurate temperature readings, as a 5% shift in supply voltage can result in a 30° C shift in indicated temperature.
Innovation Solution
A bias current generator operable in two modes, one for constant current and one for proportional-to-absolute-temperature current, is used to alternate the operation of a ring oscillator, allowing temperature determination from the ratio of output frequencies in both modes, which cancels out supply voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a ring oscillator is used as a temperature sensor, then the sensor can be easily integrated into circuitry and consume little power, but the output frequency becomes overly sensitive to power supply voltage variations, leading to inaccurate temperature readings
Solution Approach 1:
The patent changes the operating parameters of the ring oscillator by using two different bias current values (first bias current and second bias current) to generate two different output frequencies. By measuring the change in frequency as a function of this parameter change, the system can determine temperature while compensating for voltage variations, thus resolving the contradiction between ease of integration and measurement precision
Solution Approach 2:
The system uses feedback by measuring the output frequencies at two different bias current levels and using the ratio or difference of these frequencies to determine temperature. This feedback mechanism allows the system to compensate for voltage supply variations and achieve accurate temperature readings while maintaining the simplicity of the ring oscillator structure
2Device complexity
If the bias current generator operates in constant current mode, then the circuit is simpler, but the temperature sensitivity is reduced
Solution Approach 1:
The bias current generator alternates between constant current mode and proportional-to-absolute-temperature current mode in periodic fashion. This periodic action allows the system to gather information from both simple constant current operation and temperature-sensitive PTAT current operation, enabling accurate temperature measurement while managing circuit complexity through time-multiplexed operation
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 approach results in a temperature sensor that is relatively insensitive to power supply voltage variations, providing accurate temperature readings by isolating temperature-dependent frequency ratios from voltage-dependent frequency shifts.
Implementation Method 1
The output frequency of the ring-oscillator-based temperature sensor varies as a function of temperature of the integrated circuit device
Implementation Method 2
a bias current generator on the integrated circuit device, the bias current generator being selectably operable in one of (i) a first mode in which the bias current generator has a first sensitivity to temperature of the integrated circuit device and (ii) a second mode in which the bias current generator has a second sensitivity to temperature of the integrated circuit device
Data Source
AI summary
Circuitry for determining temperature of an integrated circuit device includes, on the device, a ring oscillator and a bias current generator. The bias current generator is selectably operable in (i) a first mode having a first sensitivity to device temperature or (ii) a second mode having a second sensitivity to device temperature, to provide bias current for the ring oscillator. A controller operates the bias current generator in the first mode and records a frequency output of the ring oscillator, then operates the bias current generator in the second mode and records a frequency output of the ring oscillator, and determines the temperature of the integrated circuit device from a ratio of (a) the frequency output of the ring oscillator while the bias current generator operates in the first mode to (b) the frequency output of the ring oscillator while the bias current generator operates in the second mode.