Sub-nanoampere-sensitivity current comparatorbased temperature sensor with bucket searching algorithm
Peiyong Zhang, Hangyi Lu
This Letter presents a new real-time and compact current-mode temperature sensor for system-on-chip thermal monitoring. The proposed temperature sensor provides a low-cost readout scheme that utilises a current switching comparator and dual-control bucket searching algorithm. It does not require an ADC or charged capacitor with large area and power dissipation. The dynamic element matching and threshold-setting techniques are employed to further increase the accuracy of the proposed sensor. It
... s fabricated with a standard 55 nm CMOS process, achieves an accuracy of 0.5°C while occupying a silicon area of 0.021 mm 2 , and consumes 75 mW with a 6.5 ms conversion time. Introduction: Temperature sensors are essential components of system on chip (SoC) for various applications. In addition to providing users with an interface to measure the temperature, they are also used as auxiliary components with other circuits , such as temperature calibration of ultra-high-speed interfaces. Due to this reason, the temperature sensors should have a small silicon area, low-power consumption, short conversion time and moderate resolution. Traditional bipolar junction transistor (BJT)-based voltage-mode temperature sensor exhibits excellent accuracy and resolution when used with a high-precision ADC  . However, to achieve an acceptable conversion time, this type of temperature sensor usually requires a large area or high power dissipation , which occupies precious resources needed by the core circuits. All-digital temperature sensors in time domain have better compatibility with different processes but are vulnerable to supply noise [4, 5] . They also require dedicated calibration to obtain the desired accuracy. A temperature sensor with duty-cycle-modulated output proposed in  provides an accurate and convenient readout, but the large capacitor (150 pF) increases the cost. The designers have to use such a large capacitor to obtain high accuracy and resolution, which results in long conversion time, large area, and high power consumption. Based on the shortcomings of the existing sensors, a current-mode CMOS temperature sensor with BJT-based front-end and high precision current switching comparator (CSC) is presented in this letter. The proposed structure has high accuracy and removes a large capacitor necessary for the previous current-mode temperature sensor to economise area and power consumption. Moreover, we adopt a bucket searching algorithm to achieve a fast readout. To further improve the accuracy of the CSC, dynamic element matching (DEM) and thresholdsetting techniques are applied.