BJT Dynamic Element Matching for Accurate On-Chip Temperature Sensing
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Solution Overview
Problem
Temperature sensing circuits in integrated circuits face inaccuracies due to mismatches between diode-connected bipolar junction transistors, leading to large area consumption and poor measurement reliability.
Innovation Solution
A dynamic element matching (DEM) circuit is implemented using a 1:N array of diode-connected bipolar junction transistors with force and sense switches, controlling current sources and switch logic to reduce mismatches through analog averaging at higher frequencies, effectively attenuating mismatch tones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 1:N BJT array is used for temperature sensing, then temperature measurement function is achieved, but mismatch errors occur leading to inaccurate measurements
Solution Approach 1:
The patent implements dynamic element matching by periodically rotating which BJT receives the reference current versus the scaled current through switch control. This dynamic switching converts static mismatch errors into time-varying signals that can be filtered, thereby improving temperature measurement accuracy while maintaining measurement reliability
Solution Approach 2:
The system employs periodic switching of current allocation among BJTs at a frequency higher than the mismatch tone frequency. This periodic action modulates the mismatch errors into higher frequency components that can be effectively filtered out, resolving the contradiction between measurement precision and reliability
2Measurement precision
If a 1:N current bias is implemented, then temperature sensing is enabled, but large area is consumed due to matching requirements
Solution Approach 1:
By dynamically switching the current allocation among BJTs rather than requiring all BJTs to be simultaneously matched, the patent reduces the area requirement. The switches allow temporal multiplexing of current paths, eliminating the need for large matched BJT arrays and reducing overall circuit area while maintaining temperature sensing functionality
3Productivity
If mismatch errors are present in BJT array, then temperature sensing circuit operates, but inaccurate temperature measurements result
Solution Approach 1:
The patent converts the harmful static mismatch errors into beneficial time-varying signals through periodic switching. The mismatch errors become modulated at the switching frequency, allowing them to be separated from the DC temperature signal through filtering, thus improving measurement accuracy while maintaining circuit operation
Solution Approach 2:
The switch network acts as an intermediary that periodically redistributes current among BJTs. This intermediary mechanism transforms the direct mismatch error path into a time-varying path that can be filtered, enabling accurate temperature measurement despite inherent BJT mismatches
Data Source
AI summary
An example dynamic element matching (DEM) circuit includes: a plurality of bipolar junction transistors (BJTs), each of the plurality of BJTs having a base terminal and a collector terminal coupled to electrical ground; a plurality of pairs of force switches, each pair of force switches coupled to an emitter of a respective one of the plurality of BJTs; a plurality of pairs of sense switches, where each pair of sense switches is coupled to the emitter of a respective one of the plurality of BJTs, a first switch in each pair of sense switches is coupled to a first node, and a second switch in each pair of sense switches is coupled to a second node; a first current source coupled to a first switch in each pair of force switches; and a second current source coupled to a second switch in each pair of force switches.