發(fā)布時(shí)間：2018-09-17 19:40

【摘要】：由于具有體積小、效率高、穩(wěn)定性好等優(yōu)點(diǎn),開關(guān)電源已逐漸取代傳統(tǒng)線性穩(wěn)壓器,被廣泛應(yīng)用于各類電氣電子設(shè)備的供電系統(tǒng)中。作為開關(guān)電源的重要組成部分,振蕩器不僅為系統(tǒng)時(shí)序和邏輯控制提供同步時(shí)鐘,還負(fù)責(zé)產(chǎn)生斜坡電壓對(duì)電流內(nèi)環(huán)進(jìn)行補(bǔ)償,還間接影響著系統(tǒng)芯片的面積。因此,時(shí)鐘穩(wěn)定性直接影響著開關(guān)電源性能的好壞,對(duì)高精度片內(nèi)振蕩器的研究具有極其重要的學(xué)術(shù)價(jià)值和現(xiàn)實(shí)意義。在對(duì)常見振蕩器結(jié)構(gòu)和工作原理進(jìn)行分析對(duì)比的基礎(chǔ)上,本文選擇了適用于開關(guān)電源的張弛振蕩結(jié)構(gòu)。張弛振蕩器輸出頻率容易受到環(huán)境溫度、工藝偏差、電壓波動(dòng)等因素的影響,為了補(bǔ)償時(shí)鐘頻率的穩(wěn)定性,對(duì)振蕩頻率進(jìn)行了公式推導(dǎo),表明影響頻率穩(wěn)定性的參數(shù)主要有門限電壓Vref、充電電流、比較器失調(diào)電壓Vos。在傳統(tǒng)張弛振蕩器的基礎(chǔ)上,本文提出了一種基于失調(diào)電壓補(bǔ)償?shù)母倪M(jìn)結(jié)構(gòu),使比較器門限電壓和電容充電電壓周期性地交換位置,從而削弱比較器失調(diào)電壓對(duì)時(shí)鐘頻率的影響;利用經(jīng)典的Broken帶隙結(jié)構(gòu)產(chǎn)生基準(zhǔn)電壓作為比較器門限電壓,將帶隙電路中IPTAT電流和另一路負(fù)溫度特性的電流進(jìn)行疊加,得到溫度系數(shù)為零的基準(zhǔn)電流作為振蕩器充電電流,從而實(shí)現(xiàn)對(duì)振蕩頻率的溫度補(bǔ)償;在充電電容上并聯(lián)數(shù)個(gè)大小依次減半的修調(diào)電容,當(dāng)工藝出現(xiàn)偏差時(shí),通過數(shù)字信號(hào)控制修調(diào)電容是否連接,對(duì)電容大小進(jìn)行步進(jìn)式調(diào)整,從而保證充電電容不隨工藝偏差發(fā)生變化,實(shí)現(xiàn)對(duì)輸出頻率的工藝補(bǔ)償。為了提高開關(guān)電源的電磁兼容性能,在振蕩器主體上增加了頻率擴(kuò)展模塊,通過周期性地改變充電電流的大小,使輸出頻率周期性抖動(dòng),時(shí)鐘奇次諧波處的頻帶被拓寬,降低了開關(guān)電源的電磁干擾(EMI)。此外,為了滿足開關(guān)電源在不同工作模式下對(duì)時(shí)鐘的不同需求,振蕩器還增加了分頻和占空比調(diào)節(jié)等拓展功能。振蕩器采用0.18 μm BCD工藝具體實(shí)現(xiàn),用Hspice軟件對(duì)電路進(jìn)行直流、交流和瞬態(tài)仿真,仿真結(jié)果如下:典型工作條件下,振蕩器輸出頻率為500 kHz、占空比為50%的方波時(shí)鐘;在-40-125℃的溫度范圍內(nèi),振蕩輸出頻率漂移為±0.91%;在三個(gè)不同工藝角(TT、FF、SS)條件下,時(shí)鐘頻率漂移在1.34%以內(nèi);在擴(kuò)頻模式下,輸出頻率在500 khz的中心頻率處上下抖動(dòng),抖動(dòng)范圍為±6.44%,五次諧波處的頻譜降幅高達(dá)12 dB;在降頻模式下,時(shí)鐘頻率能進(jìn)行八分頻,輸出62.5 kHz的低頻時(shí)鐘;在占空比調(diào)節(jié)模式下,可對(duì)時(shí)鐘占空比向上調(diào)節(jié)。仿真結(jié)果表明,振蕩器輸出頻率隨溫度和工藝偏差漂移較小,在擴(kuò)頻模式下能有效降低振蕩器的電磁干擾,降頻和占空比調(diào)節(jié)等拓展功能正常工作,所設(shè)計(jì)的振蕩器性能穩(wěn)定、實(shí)用性強(qiáng),適用于各類開關(guān)電源管理芯片。
[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，

本文編號(hào)：2246893