Interface electronics for a CMOS electrothermal frequency-locked-loop

2008

2008 IEEE Sensors

This work presents a CMOS temperature sensor based on thermal diffusivity sensing. This sensor is insensitive to leakage currents, and so can reliably operate up to and beyond 150ºC. Also, thermal diffusivity sensors have low intrinsic spread, which means that in many applications, they do not require trimming. A thermal diffusivity sensor and its interface circuit were realized in 0.7µm CMOS technology. The untrimmed device-to-device spread corresponds to a temperature error of ±0.7ºC (3σ) from -70ºC to 160ºC. This operating range is a significant improvement on the state-ofthe-art.

Section: Introductionsupporting

confidence: 57%

Thermal diffusivity sensors for wide-range temperature sensing

Vroonhoven

2008

2008 IEEE Sensors

“…8b). This level of accuracy is comparable to that of the analog electrothermal FLL's reported in [1][2][3]. However, these required the use of large external capacitors.…”

Section: M Eas Urement R Es Ultssupporting

confidence: 72%

“…In [1][2][3], the output frequency of an electrothermal FLL was locked to the phase shift of an ETF. Due to the temperature dependence of the thermal diffusivity of silicon, the resulting frequency is proportional to r 1.8 [1,7], where T is the absolute temperature.…”

Section: Introductionmentioning

confidence: 99%

A digitally-assisted electrothermal frequency-locked loop

Kashmiri

2009 Proceedings of ESSCIRC

2009

Self Cite

a) Figure I. The analog FLL of (I], (a), and the digitally-assisted FLL, (b).(b) '------1 II. SYSTEM-LEVEL DESIGN In Fig. 1a, a simplified block diagram of an analog FLL of [1] is shown. The YCO drives the ETF as well as a synchronous demodulator, which detects the phase of the ETF's output signal. The output of the synchronous demodulator is then integrated by an analog filter, which drives the YCO. The loop locks when the demodulator's DC output is zero, corresponding to a YCO frequency fvco = .190at which the phase shift of the ETF's near-sinusoidal output is about 90°. The FLL's phase-frequency characteristic is thus locked to that of the ETF.A block diagram of the proposed digitally-assisted electrothermal FLL is shown in Fig. 1b. Besides a YCO and an ETF, it consists of a phase domain M: modulator (PDM:M), a DAC, and a digital filter. The YCO drives the ETF, whose phase shift is then digitized by the PDM:M [5,6]. The latter's bitstream output is then compared with a phase reference of 90°, and the resulting error signal is then Hz were achieved with the help of a large (1 IlF) off-chip capacitor. In the digitally-assisted FLL described here, the noise bandwidth is defined by a digital filter, resulting in a solution that is more amenable to CMOS integration.In the next section, the system-level design of a digitallyassisted electrothermal FLL is described. Section III provides an overview of the circuit, while the measurement results are presented in section IY. The paper ends with conclusions.

“…A very stable physical effect, i.e. the thermal diffusivity of bulk silicon, could be exploited for use in frequency references [5]; however, the silicon substrate needs to be heated to measure the diffusivity and this requires a few mW. The trimmed RC oscillator described in [6] also seems to achieve performances suitable for WSN, although the effect of process spread is not discussed.…”

Section: Introductionmentioning

confidence: 99%

A low-voltage mobility-based frequency reference for crystal-less ULP radios

Foti

Breems

ESSCIRC 2008 - 34th European Solid-State Circuits Conference

et al. 2008

Abstract-The design of a 100 kHz frequency reference based on the electron mobility in a MOS transistor is presented. The proposed low-voltage low-power circuit requires no off-chip components, making it suitable for Wireless Sensor Networks (WSN) applications. After one-point calibration the spread of its output frequency is less than 1.1% (3σ) over the temperature range from -22• C to 85• C. Fabricated in a baseline 65-nm CMOS technology, the frequency reference occupies 0.11 mm 2 and draws 34 µA from a 1.2-V supply at room temperature.