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