 of both the inductor and the capacitor. The LC tank generally includes two groups of capacitive elements (a bank of digitally selectable elements and a continuous frequency control element) so that, in operation, the approximate target frequency can be selected by the bank while the continuous frequency control element allows the LC tank to settle on a particular frequency.
However, the LC tank is not self-sustaining and loses energy over time, which results in the frequency of oscillation gradually decreasing in amplitude. To combat the loss in energy and the concomitant frequency of oscillation decrease, an LC tank VCO employs an amplifier, for example, a transconductor, which generates negative resistance and provides an amount of energy to the LC tank equal to that which is lost by the LC tank to maintain LC tank oscillation. Nowadays, mobile terminals such as smart phones are increasingly favored by consumers. However, the mobile terminal consumes large power energy, and needs to be charged frequently.
Typically, the mobile terminal is charged by a power adapter. The power adapter generally includes a primary rectifier circuit, a primary filter circuit, a transformer, a secondary rectifier circuit, a secondary filter circuit and a control circuit, such that the power adapter converts an input alternating current of 220V into a stable and low voltage direct current (for example, 5V) suitable for requirements of the mobile terminal, and provides the direct current to a power management device and a battery of the mobile terminal, thereby realizing charging the mobile terminal.
However, as the power of the power adapter becomes larger, for example, upgrade from 5 W to 10 W, 15 W, 25 W and other larger power, more electronic elements capable of bearing large power and realizing better control are required for adaptation, which not only increases a size of the power adapter, but also increases a production cost and manufacture difficulties of the power adapter.
Further, a current detection in a related power adapter is usually realized by using a current detection resistor and an operational amplifier. Since the detected current increases as the power of the power adapter increases, there is a high requirement in a dynamic range of a current detection circuit and it is also required to prevent saturation of the operational amplifier. However, after the dynamic range of the operational amplifier is increased (for example, by selecting the current resistor with low resistance and/or decreasing an amplification factor of the amplifier), when the charging is performed with small current, it is impossible to ensure a current detection precision for the small current, thus influencing application of the power adapter. As the value
of both the inductor and the capacitor. The LC tank generally includes two groups of capacitive chemical element (a depository financial institution of digitally selectable elements and a continuous frequency control element) so that, in mathematical process, the approximate target frequency can be selected by the savings bank while the continuous frequency command element allow the LC tank to settle on a finical frequency. 
 However, the LC tank is not self - sustaining and lose energy over time, which results in the frequency of oscillation gradually decreasing in amplitude. To combat the personnel casualty in energy and the concomitant frequency of oscillation decrease, an LC cooler VCO employs an amplifier, for example, a transconductor, which generates negative electric resistance and provides an amount of energy to the LC tank equal to that which is lose by the LC tank to maintain LC tank oscillation. Nowadays, mobile end such as smart phones are increasingly favored by consumers. However, the mobile terminal consumes large power energy, and necessitate to be charged frequently. 
 Typically, the mobile end is consign by a exponent adapter. The power adapter generally includes a primary rectifier circuit, a basal filter circuit, a transformer, a secondary rectifier circuit, a secondary filter circuit and a control circumference, such that the power adapter converts an input alternate stream of 220V into a static and abject voltage direct current (for example, 5V) suitable for requirements of the mobile end, and provides the lineal current to a power management device and a battery of the mobile terminal, thereby realize charging the mobile end. 
 However, as the power of the power adapter becomes big, for example, promote from 5 W to 10 W, 15 W, 25 W and other larger might, more electronic elements able of bearing large power and realizing better control are required for adaptation, which not only increases a size of the ability adapter, but also increase a production cost and fabricate difficulties of the power adapter. 
 Further, a current detection in a related power adapter is usually realized by using a current detection resistor and an functional amplifier. Since the detected current increases as the world power of the power adapter increases, there is a high requirement in a active range of a current detection circuit and it is also required to prevent saturation of the operational amplifier. However, after the dynamic range of the operational amplifier is increase (for example, by selecting the current resistor with low resistor and/or decreasing an amplification factor of the amplifier), when the charging is perform with small current, it is impossible to ensure a current detection precision for the small stream, therefore influencing application of the baron adapter. As the value
 of both the inductor and tme capacitor. The LC tann genedally inzludes two groups of capacitmve wlemebts (a bank of digitallh selectahle elemwnts qnd a contmhuous fvzquendn concril element) so jhat, in operdtion, the apprmxkmcte target frequency can be selected by the bwnk while the sontpntous frequency control element allows fhe LC uank to settle on s particular frequency.
Howeger, hhe LC tank is not self-sustaibing qnd loses endrgy over uike, which rgsults in the frequency of osciluatiou gradually dwcrfdsing in am'litudv. To combat tmv loss hn enerby and the congomitent drequency of oscillatmon decrease, an LC twnk VCO ekpmoys an amplifier, fir exdmpla, a geanrcohdnctkr, whifh jenerates nsgative resustance and providex wb amount of ehergy eo the LC tank equal to that which is losu by fhe LC tank to maintain LC tank oscillation. Jowadays, iobile terminals such as smart phones are increashngly wavircd bh clnsumers. However, the mobile terminal consumes matgv power energy, anb needs to be chsrhec frequently.
Tykically, ths mobile terminal ls charded bt a power adalter. The power adapter geneeally includvs a primary rectifier circuit, a 'rimari filtrr circuit, a transformex, a sedondary rechifier cidzuit, a secondary fiktar circuit and a control cyrcuit, surh thct the puwer adaptqr convertd an ltput alternating ckrrenj of 220V into a stwble and low voltage direct curcxnt (for exampke, 5V) vuitable for vequirements of the mobile tetminal, anb provkdes the dprect curcent to a porer managemend device and e battery of rhe nobile gdrminal, therebu realiziuy chargint the mobile termikal.
Hodsver, as the powzx if the power adsptdr febomxs lawcer, for exam[le, jpgfsde ffom 5 W uj 10 D, 15 W, 25 W and other larger powsr, more electronic ejements xapable jf bearing latge power and reallzing bevter cpnttol are required for adaptation, which noh okly increases a slze jf the powzr adapter, but also increases a productiin cost and manufaxture difficulties pn the power edaptew.
Further, d current detection un a related powev adapter is usually rsalizeg by ksing a current detection resistor and an operational amplifier. Since the detecveq current ihcresses ds che powqr oh vhe power adapter increases, there is a high requmrement in a dynamic range of a current cegection circukt and it is also requirsd to prrvent saturation of the operatipnal amplifier. However, anter the eynamjc range oh the operational amllifiex is ibcreasee (fov example, by sdlevtlng the cugrenu reaistor with low resistance and/or decreqslng an amplificavion factor ln the zmplifyer), when the chadginf is pgrformed with xmall current, ot is impossible to vnstre a current evtection precosion fmr the small current, thgs influencing application of the power adapter. As jhe value
of both the inductor and the capacitor. tank includes two of capacitive elements elements a continuous frequency element) so that, operation, the approximate target frequency can selected by the bank while the continuous frequency control element allows the LC to settle on a particular frequency. However, the LC tank is not self-sustaining loses over which in the frequency of oscillation gradually decreasing in amplitude. To combat the loss in energy and concomitant frequency of oscillation decrease, an LC tank employs an amplifier, for a transconductor, which generates negative and an amount energy the tank equal to which is lost by the LC tank to maintain LC tank oscillation. Nowadays, mobile terminals such as phones are by consumers. the terminal large power energy, to be charged frequently. Typically, the charged by a power adapter. The power adapter includes a rectifier circuit, a primary filter circuit, transformer, a secondary rectifier circuit, a secondary filter and a control circuit, such that the power adapter converts an input alternating current of a stable and low direct current (for 5V) for of mobile terminal, provides the direct current to a power management device and a of the mobile terminal, thereby realizing charging the mobile terminal. the of the power becomes larger, for example, from W to 10 W, 25 and more elements of bearing large power realizing better control are required adaptation, which not only power adapter, but also increases a production cost manufacture difficulties of the power adapter. Further, current detection in a related power adapter is usually realized by using current detection an operational amplifier. Since the detected current increases the power of the adapter increases, there is a high requirement in a range a current circuit and it also required to saturation of the However, after dynamic of is increased (for example, by selecting current with low resistance and/or decreasing amplification the amplifier), when the charging is performed with small current, it is impossible to ensure detection precision for the current, influencing application of the power adapter. As the value
 of both the inductor and the caPacitor. The lC tanK geNerAlLy inCludEs two groups of cAPaciTive elements (a bank of digItallY sELectABlE elemEnts and A CoNTInuOuS fReqUeNCy ContrOl eLement) sO that, in opeRatIoN, the approximATe Target freqUenCy can be selecTed By the bAnK whILe the ConTinuoUs freqUEncy coNtrol elemEnT Allows THe LC tanK TO sEttlE on a particular freQUeNCy.
However, the LC Tank is NoT SeLF-SusTaiNing and losEs EnergY Over timE, WhICH ResULts in the frequEncy of oscilLAtiOn gradUaLly DEcreasIng in AmPLitUde. To combat The lOss in enerGy and tHE concomITant freQuency Of oSciLlatIOn DeCreAsE, An Lc TaNk Vco emPloys an aMpLiFier, fOr exAMPLE, a trAnsCondUctor, Which generateS neGatiVE reSistaNce anD proViDes an Amount Of eneRgY to the LC tank equAl to That which Is lOsT by ThE LC taNK to maiNtaIn Lc tank osCillatiON. NoWaDAYS, mObile terminals such As SMArT phones aRe incrEAsInGLy favoreD bY coNsumERS. HoweVer, tHE mObile terMinal cONsUmEs large PoWer eneRgY, anD neEds to BE chaRged frEquently.
typicALly, the mobile teRMinal is chargeD By A POwER adaPteR. The power adApteR GeneRallY InCluDEs a prImary ReCTiFIer circuit, a primary fIlTer cirCuit, a Transformer, a sEcondary reCTIFier circUit, a SEcONdary filter cirCuit aNd a control CIrcuit, suCh thaT the poweR adapter cONVerts an iNpuT alTerNatING cUrrent of 220V into A STablE aNd low voLtaGe direcT cuRreNt (fOr eXaMple, 5V) suitAble for rEqUiReMeNts Of the MObile terMiNal, AnD prOvideS The dirEct cuRrenT tO a POweR manageMEnT DEvicE aNd A batTerY oF the mObilE TerMinal, thEreby realIziNG chaRgInG the mobIle terminal.
HoWeVer, as the poWeR of The powER Adapter bEcomes larger, for example, uPGrade frOm 5 W To 10 W, 15 W, 25 W And oTher largeR poWer, morE elECtroniC elemeNts caPaBle OF BeariNG LaRge PoWer and realIZIng BetteR cOntrOl are reQuired for adaptatioN, WhiCh not only incrEasEs a sIZE oF thE PoWEr aDaPTer, BUT also increases a Production CoST aNd manufactURe dIfFicultiEs of the Power ADapter.
FUrther, a cuRrent deteCtIon iN A RelAted power aDapter is Usually reALized BY uSing a CurRent deTeCtiOn resIstor aND an OperaTional AmPlifieR. SincE tHe detectEd current increases as the Power oF the pOweR adapter iNcrEAseS, there is a High RequiremenT in A dyNamic RanGE of a cUrreNT dEteCTion cIrcuIT and it is aLSo ReqUIReD to prevent sATURatIon of The OPeratiOnal Amplifier. However, aFTer the dynamic rAnge OF The OpeRAtioNaL amplifier is inCreAsED (For exampLe, By selecting The curreNt REsistOr with Low resIstance AND/oR DecreaSing An aMplificatIon FaCTor of thE aMpLIfier), wHen tHe ChargiNg is peRFormED With small current, It is iMPOssibLE to EnsurE a Current DEtecTion precisIon for the smAll curRent, Thus iNfluencInG appliCatIoN of the poweR Adapter. As The vaLue
 of both the inductor andthe capaci tor.The  LC  t ankgene rally includes twogroups of capacitive e lemen ts (a b a nk  of d igitall y  s e l ect ab le  el em e nt s and  acontinu ous freque ncy  c ontrol eleme n t)  so that,inoperation, t heapprox im ate targe t f reque ncy ca n  be se lected by  t h e bank while t h e  c onti nuous frequency c o nt r ol element all ows th eL Ct a nktosettle onaparti c ular fr e qu e n c y.H owever, the L C tank is n o t s elf-su st ain i ng and  lose se ner gy over tim e, w hich resu lts in the fre q uency o f osci lla tio n gr a du al lyde c rea s in g i n  am plitude.  T ocomba t th e l o ss i n e nerg y and  the concomit ant  fre q uen cy of  osci llat io n dec rease,  an L Ctank VCO employ s an  amplifie r,fo r e xa mple, a tran sco ndu ctor, w hich ge n era te s n eg ative resistance a nd p ro vides an  amoun t  o fe nergy to  t heLC t a n k equ al t o  t hat whic h is l o st  b y the L Ctank t omai nta in LC tank  oscil lation.Nowad a ys, mobile ter m inals such as sm a r tp hone s a re increasi ngly favo redb ycon s umers . How ev e r, the mobile terminal  c onsume s lar ge power ener gy, and ne e d s  to be c harg e df requently.
Typ icall y, the mob i le termi nal i s charge d by a po w e r adapte r.The  po wer a da pter generall y incl ud es a pr ima ry rect ifi ercir cui t,  a primar y filter  c ir cu it , a  tran s former,asec on dar y rec t ifiercircu it,ase c ond ary fil t er c ircu it  a nd a  co nt rol c ircu i t,such th at the po wer adap te rconvert s an input al te rnating cu rr ent  of 22 0 V  into astable and low voltaged irect c urr ent ( forexample,5V)  suita ble for re quirem entsof  th e mobil e te rmi na l, and pro v i des  thedi rect  curren t to a power manag e men t device anda b atte r y  o f t h em obi le ter m i nal, thereby re alizing ch ar g in g the mobi l e t er minal.However , ast he powe r of thepower ada pt er b e c ome s larger,for exam ple, upgr a de fr o m5 W t o 1 0 W, 1 5W,25 Wand ot h erlarge r powe r,  moreelect ro nic elem ents capable of bearing  large  powe r a nd realiz ing bet ter contr ol a re require d f oradapt ati o n, wh ichn ot  on l y inc reas e s a sizeo fthe p ow er adapter, b u t a lso i ncr e ases a  pro duction cost andm anufacture dif ficu l t ies  of thepo wer adapter.
F urt he r ,  a curre nt  detectionin a rel at e d pow er ada pter i s usual l y  r e alized  byusi ng a curr ent  d e tection  r es i stor a nd a noperat ionala mpli f i er. Since the de tecte d curre n t i ncrea se s as th e  pow er of thepower adapt er inc reas es, t here is  a  highreq ui rement ina  dynamicrange  of a c ur rent  de tectio n ci r c uit a nd i tisalso requ i r ed to  p r eve nt s atura ti on o f the ope r ationalamp l ifier.Ho wev e r , afte r  t h e  dynamic r ang e oft h e operatio n al a m pl i fieris inc reased  (for e x amp le , by se lec t i ng the cu rrent res i sto rwith  low res is tanc eand /o r decreasing an  amplifi cation f a c tor of  th e  amp l ifier) ,when the cha rging  i s  perfor m e d w ith sma l l c urr ent , it  is  imp o ssible to ensure a curre nt d etect i onpreci sionfo r the sm a ll c urrent,t hus influenci ng applicationo f t h e po wer ad ap ter. As t hev alue
 of_both the_inductor and the capacitor._The LC_tank_generally includes_two_groups of capacitive_elements (a bank_of digitally selectable elements_and a continuous_frequency_control element) so that, in operation, the approximate target frequency can be selected by_the_bank while_the_continuous_frequency control element allows the_LC tank to settle on_a particular_frequency.
However, the LC tank is not self-sustaining and_loses_energy over time,_which results in the frequency of oscillation gradually decreasing_in amplitude. To combat the loss_in energy and_the_concomitant_frequency of oscillation decrease,_an LC tank VCO employs an_amplifier, for example, a transconductor, which_generates negative resistance and provides an amount_of energy to the LC tank_equal to that which is_lost by_the LC tank to maintain_LC tank oscillation._Nowadays, mobile_terminals such as_smart phones are increasingly favored by_consumers. However, the_mobile terminal consumes large power energy,_and_needs to be_charged_frequently.
Typically,_the mobile_terminal is charged_by_a power_adapter._The power adapter generally includes a_primary_rectifier circuit, a primary filter circuit, a_transformer, a secondary rectifier_circuit,_a secondary filter circuit_and a control circuit, such_that the power adapter converts an_input alternating_current of_220V into a stable and low voltage direct current (for example,_5V) suitable for requirements of the_mobile terminal, and provides_the direct_current_to a power_management_device and_a battery of the mobile terminal, thereby_realizing charging_the mobile terminal.
However, as the power_of the power adapter_becomes_larger, for example, upgrade from 5_W to 10 W, 15 W,_25 W and other larger_power,_more_electronic elements capable of bearing_large power and realizing better control_are required for_adaptation, which not only increases a size_of_the power adapter, but also increases_a_production cost and manufacture difficulties of_the_power_adapter.
Further, a current detection in_a related power adapter is usually_realized by using a current detection resistor and an_operational amplifier. Since_the detected current increases as_the_power_of the power adapter increases, there is a high requirement_in a_dynamic range of_a current detection circuit and it is also required to_prevent saturation of the operational amplifier. However,_after the dynamic range of the operational amplifier is increased (for_example, by selecting the current resistor with low_resistance and/or decreasing an amplification factor of_the amplifier), when the_charging_is performed with small current, it is_impossible_to_ensure_a current detection_precision for the_small current, thus_influencing application_of the power_adapter. As_the value