???°?ó?à????????????×????÷?????????????????°???ù??±????±????·??ó?÷?????è????????×????°?????????????ò????????×????÷?¨????????????????????·??ó?÷???????????????ù?????÷?á????·??ó?÷?????¨?????ò????·??ó?÷?á??????????????????????????????????·????????±?????¨400ns???????ù?????÷??????????????????·??????????? (40??V)??±????????????????????????????÷?????????????°????
????

?????ó??·?????×????÷?¨ADC?????????ù???????????ù?????÷????????×??????°???????÷???????????????????¨??1(a)??????????????±?????t0?±???¨???ò??????????±????????¨??1(b)??????????×????÷???????í?????????????÷?¨°ü?¨???????¨???????°???ù??±??????±??
????????×????÷???è?????±±????·?¨???????÷?????????????÷???????ó?????ù???ù?¨kT/C???ù???????????????????÷?è????×????÷?????ù?????¨?????±??????????????????×????÷????????×÷????????
???????????÷???? (TI) ?????? ADS8361 ?????? 500kHz??16 ??????×????÷???????ù?????÷????????20pF???????±???ó???? 400ns?????????????¨????×??????§?? (LSB) ?ó??????°??????????ù???ú???? (FSR) ??????????
????1 LSB = FSR / 216
???????????????????????????????????ù?è?????í (f3dB)?????????±???? (Ta=400ns)??????·??ó?÷±????¨???? LSB ????°???????16??×????÷???????????ú???? (FSR)) ??1/216+1??????????????Vin ??????×????????ù??FSR??±?????????×????????????????????×?????ú?????°???ò???????÷(Vc)??????????????????????
????Vc(t)-Vin=FSR*e-Ta/??<FSR/216+1
????-Ta/??<ln(1/216+1)=-(16+1)*ln2
??????< Ta/((16+1)*ln2)=34ns (1)
????f3dB=1/(2????) = (16+1)*ln2/(2??*Ta) = 4.7MHz (2)

????????????·??ó?÷?????????÷???????????ò?¨?????±?????????????????????±????????????????·??ó?÷×????¨??2???????á?????¨???±????
???????????è????×?????????????±??????ú?????????? ADS8361 ???????? 5V??????×?????????°??????±?????ò????·??ó?÷??×????? (SR) ±???????????
????SR = 5V/0.2??s=25V/??s??
????????×??ó???????÷±????ó????
????C=?÷Q/?÷V=I*(?÷t/?÷V)=I/SR
????I=C*SR=20pF*25V/??s=0.5mA

??????

???????????ó?à??·??ó?÷????????????????·????????????????÷????????????·??ó?÷???à??????????????±????????¨???ò????·??ó?÷???????¨???á?????????????¨??3????
????????????°??????????????¨?÷???????ì????????????????×????÷?????????????ò????DC?????????è??±???????????????·??ó?÷????×????÷???????ú???????????????????±???????±???ò??????·??ó?÷??????????
????????·???·??ó?÷?ú?ú???????è?????????÷????·??ó?÷?????????¨????·??ó?÷???????÷????·?????×è???????¨??4????
??×è??×??ó?? (Rmax) ???????????? (1) ?????????????±????????????????
?????? = Rmax * C
????Rmax = ??/ C = 1.7k??
??????×????????ú??×è????????RC×é???????é??????±??????????????????????÷C?????????????????÷Cex???í?????è??????????×????÷????????×è?¨ADC)???????ó??·??é??????????±????????ò??×????÷????????×è???????·?·??
????????×è??????????????????????×??ó???????÷????????????·??ó?÷?????á??×?????
????Imax = FSR/R (= 5V/1.7k??= 2.90mA) (3)
???????????¨???????ü???????¤??????
???????????¨?§?? (THD) ??????????????·????°???ò×??ó??×è?????á????????????????
??????×è?÷?????ù?????÷?????????????????¨???¨?÷???ò??????????×????÷???????ú???????????????????? (2) ?ù??????3dB?????????????ù?????×??
?????í????????·??ó?÷???á?????????????ù???????·±??????ù?????????????ù????×????ù·??ù???ù??????×????÷?????ù?????è×????÷???ù·??ù???ù?ó????30??V??????180??V??·???·????ù?à???¨?ó?? ADS8361??2.5LSB???????????? (2) ?ù??????4.7MHz ???í??·??ó?÷?????ù??????????
???????ù = 30??V/sqrt (4.7MHz) = 13.8nV/sqrt (Hz)
??????×????????????????????????????????¨???¨?÷????20dB/????????????????????×????÷???????????????? 3dB ?????ù???????ü???????????????è?????? 1.5???í???? ADS8361 ??????·????????ò?????á??????????????×??????ù???????????????????? sqrt(2) ?ò????
???????ù=30??V/(sqrt(2)*sqrt (4.7MHz*1.5) )= 8nV/sqrt (Hz) (4)
?????????ù??·??ó?÷?????í?????¨?????????í????3dB????
????????ADS8361?????????????? TI?? OPA227 ·??ó?÷??????????????????????×è??????1.7k???¨?ó?? 1.2k?????????°??·??ó?÷?????????????í???????ò?ó??RC(f3dB, RC=1/(2??RC)= 6.6MHz) 3dB??×??ó???????÷???????? 4.2mA?¨????(3))?????ù?????? 6.7nV?¨????(4))??OPA227 ?????ú×??ù?????ó???????????í???????á??×???????????OPA227 ??????????·??????ò?à?????????á??????·??ò????·?°?±???
????????×????÷?è?????????????°?????????????????????°?????????????????ù???????????????????????á??±??????????á?°?ì??????±??????????????°???á??????????°ü?¨·??ó?÷????????×è?????í?°???ù???????????????????????????????á??????????????????????????·????????????ó??