Abstract-This paper describes the design of a CMOS temperature-to-digital converter (TDC). It operates by measuring the temperature-dependent phase shift of an electrothermal filter (ETF). Compared to previous work, this TDC employs an ETF whose layout has been optimized to minimize the thermal phase spread caused by lithographic inaccuracy. To minimize electrical phase spread, the TDC's front-end consists of a wide bandwidth gain-boosted transconductor. The transconductor's output current is then digitized by a phase-domain 61 modulator whose phase-summing node is realized by a chopper demodulator. To minimize the residual offset caused by the demodulator's switching action, the demodulator is located at the virtual ground nodes established by the transconductor's gain-boosting amplifiers. Measurements on 16 samples (within one batch) show that the TDC has an untrimmed inaccuracy of less than 0.7 C (3 ) over the military range ( 55 C to 125 C).
Emails. [s.m.kashmiri, s.haddad, w.a.serdUn]@,ewi.tudelft.nl domain transfer function decreased overshoot in the step Abstract-The frequency-domain exponential transfer function of a response, while keeping the other characteristics fixed. delay function cannot be realized with a finite number of lumped This paper has six sections. Section II briefly recapitulates the elements. Therefore an approximation of a rational quotient of mostly used Bessel-Thomson delay-filter approximation method. polynomials has to be used. While the use of Bessel polynomials Pad6 approximation is introduced in section III, and a systemresults in the well-known all-pole Bessel-Thomson approximation, a l Taylor expansion of the exponential transfer function of a delay level overview of the delay-filter performance is investigated in around one point results in another type of rational transfer, known this section. A systematic simulation of both methods using as Pade approximation. Although a Bessel-Thomson approximation MATLABW is illustrated in section IV. The proposed method of results in an overshoot-free step response it has slower response and narrow Gaussian time-domain impulse response is discussed, smaller bandwidth in comparison to a Padc-approximated delay. simulated, and compared to the other two methods in section V. Unfortunately, the latter suffers from overshoot. To reduce the A conclusion of the derived results can be found in section VI. overshoot but preserve the fast-response and large-bandwidth properties, a new delay approximation method is introduced. The method is based on approximation of the delta time-domain II. BESSEL-THOMSON APPROXIMATION response of an ideal delay by a narrow Gaussian time-domain Bessel Thomson is the most widely used approximation method impulse response. The subsequent Pade approximation of the corulseresponding Gaussian trnsferfuenctio ylds approationa f trfer of delay filters. This method leads to a family of low-pass allcorresponding Gaussian transfer function yields a rational transfer pl rnfrfntosTs,wihwudgv prxmtl function that is ready for implementation in an analog fashion and pole transfer functions T(s), which would give approximately realizes a delay with both a large bandwidth and little overshoot. constant time delay over as large frequency range as possible.The resultant transfer functions are of the form [1]:
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