带温度补偿的扩频振荡器研究与设计
发布时间：2018-09-17 19:40
【摘要】：由于具有体积小、效率高、稳定性好等优点,开关电源已逐渐取代传统线性稳压器,被广泛应用于各类电气电子设备的供电系统中。作为开关电源的重要组成部分,振荡器不仅为系统时序和逻辑控制提供同步时钟,还负责产生斜坡电压对电流内环进行补偿,还间接影响着系统芯片的面积。因此,时钟稳定性直接影响着开关电源性能的好坏,对高精度片内振荡器的研究具有极其重要的学术价值和现实意义。在对常见振荡器结构和工作原理进行分析对比的基础上,本文选择了适用于开关电源的张弛振荡结构。张弛振荡器输出频率容易受到环境温度、工艺偏差、电压波动等因素的影响,为了补偿时钟频率的稳定性,对振荡频率进行了公式推导,表明影响频率稳定性的参数主要有门限电压Vref、充电电流、比较器失调电压Vos。在传统张弛振荡器的基础上,本文提出了一种基于失调电压补偿的改进结构,使比较器门限电压和电容充电电压周期性地交换位置,从而削弱比较器失调电压对时钟频率的影响;利用经典的Broken带隙结构产生基准电压作为比较器门限电压,将带隙电路中IPTAT电流和另一路负温度特性的电流进行叠加,得到温度系数为零的基准电流作为振荡器充电电流,从而实现对振荡频率的温度补偿;在充电电容上并联数个大小依次减半的修调电容,当工艺出现偏差时,通过数字信号控制修调电容是否连接,对电容大小进行步进式调整,从而保证充电电容不随工艺偏差发生变化,实现对输出频率的工艺补偿。为了提高开关电源的电磁兼容性能,在振荡器主体上增加了频率扩展模块,通过周期性地改变充电电流的大小,使输出频率周期性抖动,时钟奇次谐波处的频带被拓宽,降低了开关电源的电磁干扰(EMI)。此外,为了满足开关电源在不同工作模式下对时钟的不同需求,振荡器还增加了分频和占空比调节等拓展功能。振荡器采用0.18 μm BCD工艺具体实现,用Hspice软件对电路进行直流、交流和瞬态仿真,仿真结果如下:典型工作条件下,振荡器输出频率为500 kHz、占空比为50%的方波时钟;在-40-125℃的温度范围内,振荡输出频率漂移为±0.91%;在三个不同工艺角(TT、FF、SS)条件下,时钟频率漂移在1.34%以内;在扩频模式下,输出频率在500 khz的中心频率处上下抖动,抖动范围为±6.44%,五次谐波处的频谱降幅高达12 dB;在降频模式下,时钟频率能进行八分频,输出62.5 kHz的低频时钟;在占空比调节模式下,可对时钟占空比向上调节。仿真结果表明,振荡器输出频率随温度和工艺偏差漂移较小,在扩频模式下能有效降低振荡器的电磁干扰,降频和占空比调节等拓展功能正常工作,所设计的振荡器性能稳定、实用性强,适用于各类开关电源管理芯片。
[Abstract]:Because of its advantages of small size, high efficiency and good stability, switching power supply has gradually replaced the traditional linear voltage regulator and has been widely used in various electrical and electronic equipment power supply systems. As an important part of switching power supply, oscillator not only provides synchronous clock for system timing and logic control, but also produces ramp voltage to compensate the current inner loop, and indirectly affects the area of system chip. Therefore, clock stability directly affects the performance of switching power supply, and has great academic value and practical significance for the study of high precision intrachip oscillator. On the basis of analyzing and comparing the structure and working principle of common oscillator, Zhang Chi oscillatory structure suitable for switching power supply is selected in this paper. The output frequency of Zhang Chi oscillator is easily affected by environmental temperature, process deviation, voltage fluctuation and so on. In order to compensate for the stability of clock frequency, the formula of oscillation frequency is deduced. It shows that the main parameters affecting frequency stability are threshold voltage Vref, charging current, comparator offset voltage Vos. Based on the traditional Zhang Chi oscillator, an improved structure based on offset voltage compensation is proposed, in which the comparator threshold voltage and capacitor charging voltage are periodically switched. In order to weaken the influence of comparator offset voltage on clock frequency, the reference voltage generated by the classical Broken bandgap structure is used as the comparator threshold voltage, and the IPTAT current in the bandgap circuit is superposed with the other negative temperature characteristic current. The reference current with zero temperature coefficient is obtained as the charging current of the oscillator, and the temperature compensation of the oscillation frequency is realized. Through the digital signal control whether the modified capacitor is connected or not, the size of the capacitor is adjusted step by step, so as to ensure that the charge capacitance does not change with the process deviation, and realize the process compensation for the output frequency. In order to improve the EMC performance of the switching power supply, a frequency expansion module is added to the main body of the oscillator. By periodically changing the charge current, the output frequency is periodically jitter, and the frequency band at the odd harmonics of the clock is widened. The electromagnetic interference (EMI).) of switching power supply is reduced. In addition, in order to meet the different demands of the switching power supply for clock in different operation modes, the oscillator also adds the extended functions of frequency division and duty cycle adjustment. The oscillator is realized by 0.18 渭 m BCD process, and the DC, AC and transient simulation of the circuit is carried out with Hspice software. The simulation results are as follows: under typical operating conditions, the output frequency of the oscillator is 50% square wave clock with the output frequency of 500 kHz, duty cycle; In the temperature range of -40-125 鈩，
本文编号：2246893
[Abstract]:Because of its advantages of small size, high efficiency and good stability, switching power supply has gradually replaced the traditional linear voltage regulator and has been widely used in various electrical and electronic equipment power supply systems. As an important part of switching power supply, oscillator not only provides synchronous clock for system timing and logic control, but also produces ramp voltage to compensate the current inner loop, and indirectly affects the area of system chip. Therefore, clock stability directly affects the performance of switching power supply, and has great academic value and practical significance for the study of high precision intrachip oscillator. On the basis of analyzing and comparing the structure and working principle of common oscillator, Zhang Chi oscillatory structure suitable for switching power supply is selected in this paper. The output frequency of Zhang Chi oscillator is easily affected by environmental temperature, process deviation, voltage fluctuation and so on. In order to compensate for the stability of clock frequency, the formula of oscillation frequency is deduced. It shows that the main parameters affecting frequency stability are threshold voltage Vref, charging current, comparator offset voltage Vos. Based on the traditional Zhang Chi oscillator, an improved structure based on offset voltage compensation is proposed, in which the comparator threshold voltage and capacitor charging voltage are periodically switched. In order to weaken the influence of comparator offset voltage on clock frequency, the reference voltage generated by the classical Broken bandgap structure is used as the comparator threshold voltage, and the IPTAT current in the bandgap circuit is superposed with the other negative temperature characteristic current. The reference current with zero temperature coefficient is obtained as the charging current of the oscillator, and the temperature compensation of the oscillation frequency is realized. Through the digital signal control whether the modified capacitor is connected or not, the size of the capacitor is adjusted step by step, so as to ensure that the charge capacitance does not change with the process deviation, and realize the process compensation for the output frequency. In order to improve the EMC performance of the switching power supply, a frequency expansion module is added to the main body of the oscillator. By periodically changing the charge current, the output frequency is periodically jitter, and the frequency band at the odd harmonics of the clock is widened. The electromagnetic interference (EMI).) of switching power supply is reduced. In addition, in order to meet the different demands of the switching power supply for clock in different operation modes, the oscillator also adds the extended functions of frequency division and duty cycle adjustment. The oscillator is realized by 0.18 渭 m BCD process, and the DC, AC and transient simulation of the circuit is carried out with Hspice software. The simulation results are as follows: under typical operating conditions, the output frequency of the oscillator is 50% square wave clock with the output frequency of 500 kHz, duty cycle; In the temperature range of -40-125 鈩，
本文编号：2246893
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