¸ßƵģÄâÊÔÌâ¼°´ð°¸ - ͼÎÄ ÏÂÔØ±¾ÎÄ

ͼ3-3

£¨1£©V1ΪºÎÖÖÔª¼þ£¬ÆðºÎ×÷Óã¿ £¨2£©»­³öÕñµ´²¿·Ö½»Á÷ͨ·¡£

£¨3£©ÈôÊä³öµçѹuo(t)?2cos[?ct?12sin(2??103t)]V£¬Çó³ö¸ÃÐźŵÄ?fmºÍBW0.7

6-4£®±äÈݶþ¼«¹ÜÖ±½Óµ÷Ƶµç·ÖбäÈݶþ¼«¹ÜµÄr=2ʱºÍr¡Ù2ʱ¶Ôµ÷ƵϵͳÄÜÓÐʲôӰÏì?

½â£ºµ±?=2ʱ¿ÉʵÏÖÏßÐÔµ÷Ƶ£¬Ê¹µ÷ƵºóµÄ˲ʱƵÂÊËæµ÷ÖÆÐźÅÏßÐԱ仯£¬²úÉú·ÇÏßÐÔÊ§Õæ¡£µ±?²»µÈÓÚ2ʱ£¬½«²úÉú·ÇÏßÐÔÊ§ÕæºÍÖÐÐÄÆµÂÊÆ«ÒÆÊ¹µ÷ƵϵͳÐÔÄܱ仵¡£

7-1£®ËøÏ໷·ÓÉÄ¿·Ö×é³É£¬»­³ö·½¿òͼ¡£ËµÃ÷¸÷²¿·ÖÔÙ»·Â·ÖеÄ×÷Ó㬼òÊöÆä¹¤×÷Ô­Àí¡££¨10£©

½â£ºËøÏà»·Ö÷ÒªÓɼøÏàÆ÷£¨PD£©£¬»·Â·Â˲¨Æ÷£¨LF£©£¬Ñ¹¿ØÕñµ´Æ÷£¨VCO£©×é³É¡£ ¼øÏàÆ÷£¨PD£©:ÓÃÒԱȽÏui£¬uoÏà룬Êä³ö·´Ó³ÁËÏàλÎó²îµÄµçѹUd£¨t£©¡£ »·Â·Â˲¨Æ÷£ºÓÃÒÔÂ˳ýÎó²îÐźÅÖÐµÄ¸ßÆµ·ÖÁ¿ºÍÔëÒô£¬Ìá¸ßϵͳµÄÎȶ¨ÐÔ£» VCO£ºÔÙuc£¨t£©¿ØÖÆÏÂÊä³öÏàӦƵÂÊfo

£¨2£©¹¤×÷Ô­Àí£ºÈôvcoµÄwo²»µÈÓÚwi£¬ÔÙPDÖбȽÏÏà룬²úÉúÓë˲ʱÏàλ²î¡é£¨t£©³É±ÈÁеÄÎó²îµçѹuD£¨t£©¾­LFÈ¡³ö»ºÂý±ä»¯µÄÖ±Á÷¿ØÖƵçѹuc£¨t£©È¥¿ØÖÆvcoµÄƵÂʺÍÏàλÏà·´±ä»¯£¬Ê¹ui£¨t£©ºÍuo£¨t£©Ö®¼äµÄƵÂʺÍÏàλÏß¼õС£¬Ö±µ½wo=wi£¬¡é£¨t£©=³£ÊýʱΪֹ£¬ËøÏ໷·½øÈëËø¶¨×´Ì¬¡£

7-2£®ËùÏ໷·ÓÐÄÄЩÖ÷ÒªÌØµã£¿£¨6·Ö£©

´ð:ËøÏ໷·Ö÷ÒªÓÐÈý¸öÌØµã£º£¨1£©ËøÏà»·Ëø¶¨Ê±£¬ÎÞÆµÂÊÎó²î£»wo=wi£¬?£¨t£©=

41

³£Êý£¬?£¨t£©=d?£¨t£©/dt=0£»£¨2£©¾ßÓÐÕ­´øÂ˲¨ÌØÐÔ£»£¨3£©¾ßÓÐÆµÂʸú×ÙÌØÐÔ¡£

Î壮¼ÆËãÌâ 6-1¡¢ÒÑÖªµ÷ƵÐźÅ

6(t)?100cos(2??10t?20sin2??10t)(mv)UFM

mÇó£º1£®Ôز¨ÆµÂÊfc£¬µ÷ÖÆÐÅºÅÆµÂÊFºÍµ÷ÖÆÖ¸Êýf 2£®×î´óƵƫ?fm 3£®µ÷Ƶ²¨ÓÐЧ´ø¿íBW

m½â£º1£®Ôز¨ÆµÂÊfc?1MHz µ÷ÖÆÐÅºÅÆµÂÊF?1kHz µ÷ƵָÊýf=20rad 2×î´óƵƫ?fm=

mf F=20kHz

µ÷Ƶ²¨ÓÐЧ´ø¿íBW=2£¨?fm+F£©=42kH

73u(t)?3cos(4??10?10sin(2??10)) £¨V£©¼øÆµ¿çµ¼FM6-2¡¢¼øÆµÆ÷µÄÊäÈëÐźÅΪ

SD??5mV/kHz£¬ÏßÐÔ¼øÆµ·¶Î§´óÓÚ2?fm¡£ÇóÊäÈëµçѹu0(t)£® (6·Ö)

3mF½â£º ?fm=f=10?10Hz?10kHz

?u0?SD?fm=5mv/kHz?10kHz?50mv

u0(t)?s0cos(2??103t)mv

723u(t)?3cos[2??10t?5sin(2??10t)]k?10? rad/sv£¬ÊÔ£º06-3£®ÒÑÖªµ÷ƵÐźÅV£¬r£¨1£©Çó¸Ãµ÷ƵÐźŵÄ×î´óÏàÎ»Æ«ÒÆ

mf¡¢×î´óƵƫ?fmºÍÓÐЧƵÆ×´ø¿íBW£»£¨2£©¡£Ð´³ö

µ÷ÖÆÐźźÍÔØ²¨Êä³öµçѹ±íʾʽ¡££¨10·Ö£©

½â£º£¨1£©

mf=5rad£¬?fm=

mf2F=5?10Hz

BW=2£¨

mf2+1£©F=2£¨5+1£©?10Hz=1200Hz

u?(t)?U?mcos?t?£¨2£©

7U(t)?3cos2??10t c

Um2??500cos?t?cos(2??102t)?cos2??102t3Rf10?£¨v£©

6-4¡¢ÇóÏÂÁÐÁ½ÖÖÇé¿öʱ£¬µ÷ƵFMºÍµ÷ÏàPMµÄ?fmºÍBW0.7¡£

42

F=1kHz£¬

mfmp==75rad£¬U?mÏàµÈ¡£

F=10kHz£¬U?m²»±ä¡£ ½â£º£¨1£©U?mÏàµÈ£¬

mfmp=£¬ËùÒÔ?fmºÍBW0.7¶¼ÏàµÈ£º

?fm=mF=75kHz£¬

BW0.7=2£¨m+1£©F=2£¨75+1£©*1kHz=152kHz U?m²»±ä£¬Ôò£º FM£º?fm=PM£º

kfU?m?75kHz²»±ä£¬BW=

2(?fm?1)F?170kHzF

mp=75 rad£¬²»±ä?fm=

mpF=75?10kHz

BW=2£¨

mp+1£©F=2£¨75+1£©?10kHz=1520kHz

63u(t)?3cos[2??10t?10sin(2??10t)]£¨v£©6-5¡¢ÓÐÒ»µ÷ƵÐźűí´ïʽΪ£ºFM£¬ÊÔ¸ù¾Ý

±í´ïʽ·Ö±ðÈ·¶¨£º£¨1£©¡¢×î´óƵƫ£»£¨2£©¡¢×î´óÏàÒÆ100?µç×èÉÏµÄÆ½¾ù¹¦ÂÊ¡££¨8·Ö£©

½â£º£¨1£©

mf£»£¨3£©¡¢ÐźŴø¿í£»£¨4£©¡¢inhaoÔÚ

?fm?mf?F?10?103?10kHz2(mf?1)F?22kHz2£¨2£©??m?10rad

£¨3£©BW=£¨4£©

PAV

cm?U2RL?0.5W

6-6µ÷ÖÆÆµÂÊF=10Hz~100kHz£®×î´óƵƫ?fm?75kHz£¬U?m²»±ä£¬¼ÆËãµ÷Ƶ´ø¿í¶ÈBWÈçºÎ±ä»¯£¿µÃ³öʲô½áÂÛ£¿

½â£º£¨1£©FM²¨£ºF1=10Hz£¬BWf1=2£¨

mf1??fm/F1?75?103/10?7.5?103

mf3+1£©F1=2£¨7£®5+1£©?10=150?10Hz=150kHz

F2?10kHz,mf2??fm/F2?75?103/10?103?7.5radBW

f2

=

(mf2?1)F2?2(7.5?1)?10?103?170?103Hz?170kHz£¬²»±ä

Mp?75?103rad

43

£¨2£©PM²¨£º±¶¡£

BWp?2(7500?1)(10~10?103)?150kHz~150?103£¬±ä»¯Ô¼Îª1000

½áÂÛ£º£¨1£©FMµÄF±ä»¯1000±¶¡£ £¨2£©PMµÄ±ä»¯1000±¶£¬ÎÞ·¨ÊµÏֵġ£

BWf´Ó150kHz~170kHz£¬¼¸ºõ²»±ä£¬ÂÔÔö15%¡£

3BWp´Ó150kHz~150?10kHz£¬±ä»¯Îª1000±¶£¬ÊÇ

6-7¡¢Ä³µ÷Ƶ·¢Éä»ú¿òͼÈçÏÂͼËùʾ£¬µ÷ƵÆ÷Êä³öFMÐźŠµÄÖÐÐŤ×÷ƵÂÊ

fc?8MHz£¬×î´óƵƫ?fm?40kHz¿òͼÖÐ»ìÆµÆ÷Êä³öÈ¡²îƵÐźţ»Èô×î¸ßµ÷ÖÆÆµÂÊFmax?15kHz£¬Çó£º

¸ÃÉ豸Êä³öÐźŵÄÖÐÐÄÆµÂÊf0¼°×î´óƵƫ?fmo£»

·Å´óÆ÷1ºÍ·Å´óÆ÷2Êä³öµÄÐźÅÖÐÐÄÆµÂÊÓëÆµÆ×´ø¿í¸÷Ϊ¶àÉÙ£¿

½â£º1£® Êä³öÐźŵÄÖÐÐÄÆµÂÊf0=3*8-15=9MHz ×î´óƵƫ?fmo=120kHz ·Å´óÆ÷1Êä³öµÄÖÐÐÄÆµÂÊΪ8MHz£¬BW=2*£¨15+40£©=110kHz ·Å´óÆ÷2ºô³öµÄÖÐÐÄÆµÂÊΪ9MHz£¬BW=2*£¨15+120£©=270kHz

33u?5cos2??10tu?cos2??10t£¨v£©c?t6-8¡¢Ôز¨£¨v£©£¬µ÷ÖÆÐźÅ×î´óƵƫ?fm?20kHz

Ç󣺣¨1£©µ÷Ƶ²¨±í´ïʽ£» £¨2£©µ÷ƵϵÊý

mfºÍÓÐЧ´ø¿íBW£»

3 £¨3£©Èôµ÷ÖÆÐźÅu?(t)?3cos2??10t£¨v£©£¬Ôòmr=£¿BW=£¿ ½â£º£¨1£©

mf??fm/F?20rad

uFM(t)?5cos(2??108t?20sin2??103t)£¨v£©

44