Fast start crystal oscillator design with negative resistance control |
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Affiliation: | 1. School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024, PR China;2. Key Laboratory of Inorganic Coating Materials, Chinese Academy of Sciences, Shanghai 200050, PR China;1. Electronic Design Centre, Department of Electronic Engineering, NED University of Engineering and Technology, P.O. Box 75270, Karachi, Pakistan;2. Electrical Engineering Department, United Arab Emirates University, P.O. Box 15551, Al-Ain, UAE;3. IFM Department, Linkoping University, Sweden;1. School of Computer and Information, Hefei University of Technology, 193 Tunxi Road, Hefei 230009, China;2. School of Electronic Science&Applied Physics, Hefei University of Technology, 193 Tunxi Road, Hefei 230009, China |
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Abstract: | Clock is an essential part of most of the integrated circuits as time base reference. It must be very accurate, highly reliable and readily available as soon as it is enabled. In all types of oscillator architectures, crystal oscillator is the most accurate and stable clock generator. But usually the crystal oscillator circuit suffers from slow startup. Therefore, it is essential to improve the startup time with optimally controlled crystal drive such that crystal drive power rating is not compromised. We propose a method that discusses about increasing the negative resistance during startup, using a startup circuit for fast start. Once the reliable startup is achieved, the negative resistance is decreased and the startup circuit is disconnected. The reduction in negative resistance is done with current steps and there are two ways in which it is achieved, the Digital control method and Analog control method. In digital control method, the current steps are timed at regular intervals and in analog control method, oscillator output amplitude is given as feedback to the startup circuit there by reducing the negative resistance. In the 32768 Hz real time clock generating oscillator, the startup time can be improved from 330 ms to 220 ms using the conventional startup method. With the proposed digital control method, lesser startup time of 160 ms is achieved and in analog control method it is further reduced to 120 ms. |
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Keywords: | Crystal oscillator Startup circuit Stable clock generator Gm-stage |
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