石英(ying)晶體振蕩器的(de)應用(yong)

石(shi)(shi)英(ying)(ying)鐘(zhong)走(zou)(zou)時(shi)(shi)準(zhun)、耗電(dian)(dian)省為(wei)(wei)其優點。不論(lun)是老式石(shi)(shi)英(ying)(ying)鐘(zhong)或(huo)是新(xin)式多功能石(shi)(shi)英(ying)(ying)鐘(zhong)都是以(yi)石(shi)(shi)英(ying)(ying)晶(jing)體振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)為(wei)(wei)電(dian)(dian)路(lu)，其頻(pin)率精(jing)(jing)度(du)決(jue)定了電(dian)(dian)子鐘(zhong)表的(de)走(zou)(zou)時(shi)(shi)精(jing)(jing)度(du)。石(shi)(shi)英(ying)(ying)晶(jing)體振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)原(yuan)理(li)的(de)示(shi)意如圖3所(suo)(suo)示(shi)，其中V1和V2構(gou)成(cheng)CMOS反相器(qi)(qi)石(shi)(shi)英(ying)(ying)晶(jing)體Q與振(zhen)(zhen)蕩(dang)(dang)電(dian)(dian)容(rong)(rong)C1及微調(diao)電(dian)(dian)容(rong)(rong)C2構(gou)成(cheng)振(zhen)(zhen)蕩(dang)(dang)系(xi)統(tong)，差(cha)分(fen)晶(jing)振(zhen)(zhen)，這里石(shi)(shi)英(ying)(ying)晶(jing)體相當于(yu)電(dian)(dian)感。振(zhen)(zhen)蕩(dang)(dang)系(xi)統(tong)的(de)元件參(can)數確定了振(zhen)(zhen)頻(pin)率。一般(ban)Q、C1及C2均為(wei)(wei)外接(jie)元件。另外R1為(wei)(wei)反饋電(dian)(dian)阻(zu)，差(cha)分(fen)晶(jing)振(zhen)(zhen)原(yuan)廠(chang)，R2為(wei)(wei)振(zhen)(zhen)蕩(dang)(dang)的(de)穩定電(dian)(dian)阻(zu)，差(cha)分(fen)晶(jing)振(zhen)(zhen)加(jia)工，它們都集(ji)成(cheng)在(zai)電(dian)(dian)路(lu)內部。故無法通過改變(bian)C1或(huo)C2的(de)數值來調(diao)整走(zou)(zou)時(shi)(shi)精(jing)(jing)度(du)。但此時(shi)(shi)仍(reng)可用加(jia)接(jie)一只(zhi)電(dian)(dian)容(rong)(rong)C有方法，來改變(bian)振(zhen)(zhen)蕩(dang)(dang)系(xi)統(tong)參(can)數，以(yi)調(diao)整走(zou)(zou)時(shi)(shi)精(jing)(jing)度(du)。根據電(dian)(dian)子鐘(zhong)表走(zou)(zou)時(shi)(shi)的(de)快慢，調(diao)整電(dian)(dian)容(rong)(rong)有兩種接(jie)法:若走(zou)(zou)時(shi)(shi)偏快，則(ze)可在(zai)石(shi)(shi)英(ying)(ying)晶(jing)體兩端并(bing)接(jie)電(dian)(dian)容(rong)(rong)C，如圖4所(suo)(suo)示(shi)。此時(shi)(shi)系(xi)統(tong)總電(dian)(dian)容(rong)(rong)加(jia)大，振(zhen)(zhen)蕩(dang)(dang)頻(pin)率變(bian)低，走(zou)(zou)時(shi)(shi)減慢。若走(zou)(zou)時(shi)(shi)偏慢，則(ze)可在(zai)晶(jing)體支路(lu)中串接(jie)電(dian)(dian)容(rong)(rong)C。如圖5所(suo)(suo)示(shi)。此時(shi)(shi)系(xi)統(tong)的(de)總電(dian)(dian)容(rong)(rong)減小，振(zhen)(zhen)蕩(dang)(dang)頻(pin)率變(bian)高(gao)，走(zou)(zou)時(shi)(shi)增快。只(zhi)要經(jing)過耐(nai)心的(de)反復試驗(yan)，就可以(yi)調(diao)整走(zou)(zou)時(shi)(shi)精(jing)(jing)度(du)。因此，晶(jing)振(zhen)(zhen)可用于(yu)時(shi)(shi)鐘(zhong)信號發生器(qi)(qi)。

振蕩器的常見指標

初始(shi)準確(que)率:指(zhi)振(zhen)蕩器上(shang)電工(gong)作(zuo)某(mou)一段短時間內的(de)頻(pin)率準確(que)度:—般為開機八分(fen)鐘至30分(fen)鐘，25度室溫(wen)，需要等到晶振(zhen)穩定工(gong)作(zuo)

老化率:振蕩(dang)器在工作一段時(shi)間(jian)后由于內部結構(gou)的改變引起的頻率偏移

引起原因:不同(tong)的(de)(de)熱膨脹(zhang)系數(shu)、焊接(jie)材料在(zai)(zai)凝固、加(jia)工時(shi)尺寸的(de)(de)改變、由于成(cheng)型，差分晶振價格，焊接(jie)時(shi)的(de)(de)殘余應力，電(dian)極(ji)的(de)(de)內應力、石英在(zai)(zai)生(sheng)長中的(de)(de)不均勻，雜質和(he)其他缺陷、切割(ge)，點清晰和(he)腐蝕(shi)引起的(de)(de)表(biao)面破壞(huai)的(de)(de)影響、電(dian)極(ji)應力和(he)支架為對準的(de)(de)彎(wan)矩(ju)，晶格內部產生(sheng)局部化(hua)應力產生(sheng)的(de)(de)破壞(huai)

根(gen)據測(ce)試(shi)時(shi)長老化率一(yi)般分日老化率、月老化了(le)、年老化率。

選擇振(zhen)蕩(dang)器時需要考慮哪些因素(su)

選擇振蕩(dang)(dang)器(qi)時(shi)需要考慮(lv)功(gong)(gong)(gong)耗(hao)。分立振蕩(dang)(dang)器(qi)的(de)(de)功(gong)(gong)(gong)耗(hao)主要由反(fan)饋放大(da)器(qi)的(de)(de)電(dian)(dian)源電(dian)(dian)流以(yi)及(ji)電(dian)(dian)路(lu)內部的(de)(de)電(dian)(dian)容值(zhi)所(suo)決定。CMOS放大(da)器(qi)功(gong)(gong)(gong)耗(hao)與(yu)工(gong)(gong)作頻率(lv)成正比，可(ke)以(yi)表(biao)示為功(gong)(gong)(gong)率(lv)耗(hao)散電(dian)(dian)容值(zhi)。比如，HC04反(fan)相器(qi)門電(dian)(dian)路(lu)的(de)(de)功(gong)(gong)(gong)率(lv)耗(hao)散電(dian)(dian)容值(zhi)是90pF。在(zai)4MHz、5V電(dian)(dian)源下工(gong)(gong)作時(shi)，相當(dang)于(yu)1.8mA的(de)(de)電(dian)(dian)源電(dian)(dian)流。再加上(shang)20pF的(de)(de)晶振負載電(dian)(dian)容，整個電(dian)(dian)源電(dian)(dian)流為2.2mA。陶(tao)瓷(ci)諧振槽(cao)路(lu)一般(ban)具有(you)較大(da)的(de)(de)負載電(dian)(dian)容，相應地也需要更多(duo)的(de)(de)電(dian)(dian)流。相比之下，晶振模塊一般(ban)需要電(dian)(dian)源電(dian)(dian)流為10mA ~60mA。硅振蕩(dang)(dang)器(qi)的(de)(de)電(dian)(dian)源電(dian)(dian)流取決于(yu)其(qi)類型與(yu)功(gong)(gong)(gong)能，范(fan)圍可(ke)以(yi)從低(di)頻（固定）器(qi)件(jian)的(de)(de)幾(ji)個微安到可(ke)編程(cheng)器(qi)件(jian)的(de)(de)幾(ji)個毫安。一種低(di)功(gong)(gong)(gong)率(lv)的(de)(de)硅振蕩(dang)(dang)器(qi)，如MAX7375，工(gong)(gong)作在(zai)4MHz時(shi)只(zhi)需不(bu)到2mA的(de)(de)電(dian)(dian)流。在(zai)特定的(de)(de)應用(yong)場合(he)優化時(shi)鐘源需要綜合(he)考慮(lv)以(yi)下一些因素：精(jing)度、成本、功(gong)(gong)(gong)耗(hao)以(yi)及(ji)環境(jing)需求。