Sigma-Delta Thermal Sensor Scaling Without Capacitor Mismatch
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Solution Overview
Problem
Current temperature sensing circuits in Systems on a Chip (SOCs) face errors in temperature measurement due to mismatch in capacitance values of sampling capacitors, which affects the accuracy of the digital temperature reading.
Innovation Solution
A temperature sensor circuit utilizing a switched capacitor sigma-delta modulated analog to digital converter that samples and integrates voltages proportional to absolute temperature and a temperature-independent reference voltage, allowing for accurate scaling of these voltages in the time domain without the need for dynamic element matching, thereby reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sampling capacitors are used to scale Vptat and Vref, then voltage scaling is achieved, but mismatch errors occur due to capacitance value variations
Solution Approach 1:
The patent replaces the mechanical/electrical capacitor-based voltage scaling system with a time-domain scaling system using a sigma-delta modulator. Instead of using sampling capacitors with fixed capacitance values to scale voltages, the invention uses a modulator that performs scaling through time-domain operations (modulation and demodulation), thereby eliminating mismatch errors caused by capacitor fabrication variations.
Solution Approach 2:
The patent changes the parameter domain from spatial (capacitance values) to temporal (time-domain operations). By performing voltage scaling in the time domain through sigma-delta modulation rather than through capacitor ratios, the invention transforms the scaling mechanism to one that is insensitive to component mismatches.
2Measurement precision
If dynamic element matching hardware is used to correct capacitor mismatch, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the complex dynamic element matching hardware from the system by fundamentally changing the approach to voltage scaling. Instead of adding correction hardware to compensate for capacitor mismatches, the invention eliminates the source of mismatches by performing scaling in the time domain, thereby simplifying the overall device architecture.
Solution Approach 2:
The patent replaces the complex hardware-based dynamic element matching system with a time-domain processing approach using sigma-delta modulation. This substitution eliminates the need for additional matching hardware while maintaining or improving measurement accuracy.
Data Source
AI summary
A temperature sensing circuit a switched capacitor circuit selectively samples ΔVbe and Vbe voltages and provides the sampled voltages to inputs of an integrator. A quantization circuit quantizes outputs of the integrator to produce a bitstream. When a most recent bit of the bitstream is a logic zero, operation includes sampling and integration of ΔVbe a first given number of times to produce a voltage proportional to absolute temperature. When the most recent bit of the bitstream is a logic one, operation includes cause sampling and integration of Vbe a second given number of times to produce a voltage complementary to absolute temperature. A low pass filter and decimator filters and decimates the bitstream produced by the quantization circuit to produce a signal indicative of a temperature of a chip into which the temperature sensing circuit is placed.