A Poly Resistor Based Time Domain CMOS Temperature Sensor with 9b SAR and Fine Delay Line

Abstract

This paper presents a new type of time domain CMOS temperature sensor with a 9b successive approximation register (SAR) control logic and a fine delay line. We adopted an N-type poly resistor as the sensing element for temperature linearity. The chip was implemented in a standard 0.18 m 1P6M bulk CMOS process with general VTH transistors and the active die area was 0.432 mm2. The temperature resolution was 0.49 °C and the temperature error was from −1.6 to +0.6 °C over the range of 0 to 100 °C after two-point calibration. The supply voltage sensitivity was 0.085 °C/mV. The conversion rate was 25kHz and the energy efficiency was 7.2 nJ/sample.

A 0.026 mm2 Time Domain CMOS Temperature Sensor with Simple Current Source

“…In this paper, in regard to the detailed definition of the temperature estimation function, we introduced and explained the 12 types of operational principles and the corresponding temperature estimation functions of the time domain CMOS temperature sensors from our previous work [ 1 ]. Finally, the START signal enables the 11b binary counter and the additional logic circuit to start the operation of this time domain CMOS temperature sensor.…”

“…Figure 1 shows the conventional current source based on a single n -type poly resistor [ 1 , 8 , 9 , 13 ]. It consists of multiple diode-connected PMOS transistors between V DD and the ground, a differential input to a single-ended output amplifier, an n -type poly resistor and a PMOS transistor.…”

“…Due to their small form factor, low power consumption, low cost and convenient digital interface capability, integrated temperature sensor chips have been widely used for thermal monitoring in various smart applications such as the smart farm, smart factory, smart health, and so on. Integrated temperature sensor chips can be implemented in various ways depending on the sensing element which is generally chosen from the threshold voltage, mobility, resistance or thermal voltage; the measured signal type, which is generally chosen from the voltage, current, frequency, or delay time; and the overall architecture which is basically determined by the chosen sensing element and the measured signal type [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ].…”

“…Among the possible architectures, a time domain architecture based on frequency or delay time is promising because it can benefit from the recent trend that time resolution is being increased while voltage resolution is being decreased as the CMOS channel length and the supply voltage are scaled down. By measuring time domain signals such as the clock frequency, clock period or delay time, an efficient estimate of the current temperature can be obtained [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. The sensing element can be chosen from the mobility, threshold voltage or resistance.…”

Categorization and Characterization of Time Domain CMOS Temperature Sensors

“…The previously published time domain CMOS temperature sensors in literature [ 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ] can be categorized into one of the types 3, 4, 5, 7, 8, 11 and 12, respectively, as shown in Figure 4 . In this section, their temperature estimation functions, X(T), are derived first and then characterized as follows.…”