| Switching mode power supply technology has been well developed and has become widely used in today's electronic world. The DC switching mode power supply occupies the largest market share, especially DC to DC converters. A synchronizable oscillator for the application in DC to DC converters is presented in this paper. For this kind of application, the request for the oscillator's frequency stability is not as strict as for that of communication products, but it has a higher stability request for its duty cycle. Therefore, to meet the frequency and duty cycle stability requirements, the key sub-blocks such as the comparator and the bias block which provides a supply-insensitive and temperature-insensitive current to bias the oscillator are carefully designed in order to acquire a supply-insensitive, temperature-insensitive and process-insensitive output oscillator frequency.A special function of the oscillator designed here is the synchronization to external frequencies, that is, when the frequency and duty cycle of the external clock signal are different from that of the oscillator's, the oscillator changes automatically its frequency and duty cycle to that of the clock signal's so that a unique frequency is presented in the IC. What's special is that in the application of external synchronization, the range of the external frequency is extended (it can be smaller than the oscillator's intrinsic frequency) and the duty cycle of the oscillator's frequency is controlled only by its internal circuitry. While the duty cycle of the external frequency varies greatly, the duty cycle of the oscillator frequency is kept to be constant (usually 80%), and the cycle is synchronized to the external frequency.The key parameters of the oscillator are finally verified by Hspice simulation results. Comparison between the oscillator designed and an oscillator product Maxim7387 widely used in today's power supply market indicates that the oscillator designed here can be widely used in IP applications. |
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