1、 1994-2010 China Academic Journal Electronic Publishing House. All rights reserved. http:/第 29 卷 第 8 期2008 年 8 月半 导 体 学 报J OU RNAL O F S EMICOND U C TO RSVol. 29 No. 8Aug. ,20083 Project supp orted by t he National Natural Science Foundation of China ( No. 90707002) a nd t he Natural Science Foundat
2、ion of Zhejiang Province(No. Z104441) Corresp onding aut hor . Email :zhaoml zju. edu. cnReceived 26 J a nuary 2008 , revised ma nuscript received 29 February 2008 Z 2008 Chinese Institute of ElectronicsDesign of a Bandgap Reference with a Wide Supply Voltage Range 3Sun Yueming , Zhao Menglian , and
3、 Wu Xiaobo( I nstitute of V L S I Desi gn , Zhej iang Universit y , Hangz hou 310027 , China)Abstract : A n on2chip voltage reference wit h a wide supply voltage range is required by some applications , esp ecially t hatof p ower management ( PM) cont roller chips applied t o telecommunication , aut
4、 omotive , lighting equip ment , etc. , w henhigh p ower supply voltage is needed. Accordingly ,a new bandgap ref erence wit h a wide supply voltage range is p rop osed.Due t o t he imp roved st ructure ,it f eatures a high p ower supply rejection ratio ( PS R R) and high temperature stability. Inad
5、dition ,an auxiliary micro2p ower ref erence is int roduced t o supp ort t he sleep mode of t he PM chip and reduce its standbyp ower consump tion. The auxiliary ref erence p rovides bias currents in normal mode and a 1128V ref erence voltage in sleepmode t o replace t he main ref erence and save p
6、ower. Simulation results show t hat t he ref erence p rovides a ref erence volt2age of 1127V ,w hich has a 315mV drif t over t he temperature range f rom - 20 t o 120 and 56 V deviation over a supplyvoltage range f rom 3 t o 40V . The PSR R is higher t han 100dB f or f requency below 10k Hz. The cir
7、cuit was completed in115 m B CD (Bip olar2CMOS2DMOS) technology. The exp erimental results show t hat all main expectations are achieved.Key words : wide supply voltage range ; bandgap ref erence ; line regulation ; sleep mode ; micro p owerEEACC : 2570ACLC number : TN433 Document code : A Article I
8、D : 025324177 (2008) 08215292061 IntroductionBandgap reference is widely applied in most analogand mixed signal integrated circuit s ( ICs) . Since someICs ,especially PM ICs , work under a wide operatingvoltage range ,typically 24V/ 48V in communication ap2parat us , 14V/ 42V in automobiles , and 3
9、 to 40V inlighting such as L ED equip ment . Thus ,a bandgap ref2erence capable of operating wit h a wide supply voltagerange is demanded in such applications.As a voltage reference , the bandgap referenceshould provide a voltage independent of power supplyand temperat ure. Moreover ,high PSRR is al
10、so a criticalfeat ure since the power supply ripples will affect it sstability1 and influence it s outp ut reference voltage.A typical bandgap reference contains two voltagesources wit h opposite temperat ure coefficient s ( TC) tocompensate it s temperat ure drift . The positive TC( P TC) voltage s
11、ource consist s of a transistor pair wit hdifferent emitter areas. Their base2emitter voltagedifference ( V BE) is an ideal P TC voltage source. Thevoltage with negative TC ( N TC) is derived f rom t heforward voltages of p n junctions. By aboratively matc2hing t he opposite TCs of two voltage sourc
12、es ,accuratetemperat ure compensation can be achieved over a cer2tain range2 ,3 .In t he conventional topology , the off set voltage(V OS) of t he amplifier is a major error source and is un2predictable since it is a random error produced fromdispersion during t he manufact uring process4 . Moreo2ve
13、r , this struct ure restrict s t he operating supply volt2age range because t he common mode inp ut voltage oft he amplifier is limited5 . The margin of the amplifieralso restrict s t he PSRR.In t his paper ,a novel bandgap reference struct ureis proposed. Different f rom conventional struct ures ,i
14、t sP TC voltage is directly generated by an inner ampli2fier. Moreover ,t he inner amplifier is supplied by a pre2regulated reference voltage , which guarantees it s nor2mal operation over a wide supply voltage range. It alsoeffectively improves t he PSRR and load regulation oft he reference. The no
15、vel bandgap reference was imple2mented in 115 m BCD ( bipolar2CMOS2DMOS) tech2nology and verified by experimental result s.2 Proposed bandgap referenceFigure 1 shows a conventional bandgap referenceand Figure 2 shows the complete schematic of t he pro2posed bandgap reference. The reference is differ
16、entf rom conventional one. It is composed of two part s : amicro2power reference and a power supply independentbandgap reference. It can be implanted in2to a typical 1994-2010 China Academic Journal Electronic Publishing House. All rights reserved. http:/半 导 体 学 报 第 29 卷Fig. 1 Conventional bandgap r
17、eferenceswitch mode power supply ( SMPS) controller IC. Inaddition , it support s t he prevailing sleep2mode tech2nique. When t he controller is shut down ,only t he mi2cro2power reference is active ,providing a rough t hresh2old voltage for t he startup comparator. While t he con2troller is working
18、 ,t he supply2independent bandgap ref2erence will be activated to provide a more precise refer2ence voltage.2. 1 Micro2power referenceThis circuit has two characteristics : providing aprimary reference voltage of 1128V for the RUN com2parator when t he controller is in sleep mode and p rovi2ding a P
19、 TA T current for t he supply2independentbandgap reference and ot her circuit blocks when t hecontroller is working. While working as the primaryreference , it s typical quiescent current is less t han10 A ,which makes it feat ure micro2power dissipation.By using transistors that can endure high vol
20、tage , itcan be directly supplied by V IN ,which may vary f rom 3to 40V.The principle of t his circuit is shown in Fig13.Here , m is t he ratio of t he emitter areas of QA2and QA1 , is t he current gain of M1 M3 ,and is t hecurrent gain of M4 M6. A resistor R1 of several megaohms determines the curr
21、ent IA . The forward voltagesof t he base2emitter (V BE) of QA1 and QA2 are :VB E_QA1 = V Tl n IM2Iss(1)Fig. 2 Proposed supply2independent bandgap referenceFig. 3 Micro2power referenceVB E_QA2 = V T l n IM3m Iss(2)where V T = k T/ q , k is t he Boltzmann s constant , q ist he electron charge , T is
22、t he temperat ure in Kelvin (orabsolute temperat ure) ,and ISS is t he reverse sat urationcurrent of t he base2emitter junction of QA1.U sing t he current mirror M1 M3 ,t he current IM2and IM3 is :IM2 = IM3 = IA (3)Then t he voltage across R2 and R3 becomes :V R2 = IM2 R2 = IA R2 (4)VR3 = ( IM3 + IM
23、4 ) R3 = ( IA + IB ) R3 (5)Because QA1 and QA2 share t he same base node ,t he base voltage is :VB E_QA1 + V R2 = VB E_QA2 + V R3 (6)From Eqs. (1) (5) ,we can derive :R3 IB + IA ( R3 - R2 ) = V T l n m (7)Here , R2 is equal to R3 . Thus ,a proportional to abso2lute temperature ( P TA T) current is o
24、btained as :IB = V T l n mR3(8)Therefore ,t he outp ut voltage of the micro2powervoltage reference is :V R EF1 = VB E_QA4 + IPTA T R5= VB E_QA4 + R5 V T l n mR3(9)where V BE_QA4 has a negative temperature coefficient .Thus ,a stable reference voltage wit h a near zero tem2perat ure coefficient can b
25、e obtained by choosing appro2priate values of , R3 , R5 ,and m.Because the bias current IA is generated by R1 ,t hisreference does not need a start up circuit . Moreover ,t heaccuracy of R1 is not critical because t he reference volt2age does not depend upon IA .Transistors M7 and QA3 form a feedbac
26、k loop tokeep QA1 and QA2 working in t he forward active re2gion. If t he supply voltage V IN rises ,t he voltage acro ssR2 and R3 will also rise ,as well as t he gate voltage ofM7. Then t he current flowing t hrough M7 and QA3 ri2ses too ,p ulling up t he base voltage of QA3 ,QA1 ,and0351 1994-2010
27、 China Academic Journal Electronic Publishing House. All rights reserved. http:/第 8 期 Sun Yueming et al . : Design of a Bandgap Reference with a Wide Supply Voltage RangeFig. 4 Proposed supply2independent bandgap referenceQA2. As a result , QA1 and QA2 keep t heir stat us int he forward active regio
28、n. Transistor M6 works as avoltage controlled resistor. Because R2 equals R3 ,whensupply voltage V IN climbs up ,t he voltage variation overgate and source nodes of M6 is approximately equal. Sot he current flowing t hrough M6 is not influenced byt he supply voltage.In t he layout of t his bandgap r
29、eference , R5 is re2placed by several trimmable resistors to achieve a pre2cise predicted reference voltage after tape2outing.2. 2 Supply2independent bandgap referenceU sing a unique struct ure to generate t he referencevoltage , t he bandgap reference has good line regula2tion. Different f rom t he
30、 micro2power reference above ,itcan supply a current up to 1mA ,which is significant tot he SMPS controller. In addition ,t his reference can beshut down in sleep mode to save power. The detailedcircuit is shown in Fig14.U sually , bipolar transistors have a smaller off setand higher gain t han MOS
31、transistors6 . Thus ,bipolartransistors are adopted as inp ut differential pairs to re2duce the off set and to provide a higher gain.Here ,t he parameter n is t he ratio of the emitterjunction sizes of QB3 and QB4. Ibias is a bias currentprovided by the micro2power reference. TransistorsQB1 QB4 and
32、resistor R9 constitute an O TA circuit .While working stably , t he current s flowing t hroughQB3 , QB4 differential pairs will tend to be equal.Thus ,t he difference of the base2emitter voltage of QB3and QB4 is : VB E = VB E_QB3 - VB E_QB4= V T l n IQB3Iss- V T l n IQB4nIss= V T l n n (10)The base
33、nodes of QB3 and QB4 clamp t he voltagedrop across R7 , generating a P TA T current t hroughFig. 5 Reversed nested Miller compensationR7 . The reference voltage includes two part s :t he P TCvoltage across R6 and R7 , which is produced by t heP TA T current ,and t he N TC voltage of V BE .V R EF = V
34、B E_QB5 + VB ER7( R6 + R7 )= VB E_QB5 + V T l n nR7( R6 + R7 ) (11)Transistors QB6 QB9 constit ute a feedback loopto stabilize t he collector current of QB5. If t his currentfalls ,t he voltage across R7 will become smaller ,whichis amplified by the O TA. The base of QB6 is connectedto t he reverse
35、outp ut terminal of O TA ;therefore ,it al2so rises. Transistor QB7 is biased by QB5 ,so it alwaysworks in the forward active region. QB6 and QB7 canbe regarded as a simple amplifier. Therefore ,t he volt2age rising of t he base of QB6 causes a significant reduc2tion in t he collector current of QB8
36、 and t hen an in2crease in t he base voltage of QB9. As a result ,t he cur2rent flowing t hrough R6 , R7 , and QB5 rises and suc2ceeds in compensating t he initial current fluct uation.Thus ,t he current flowing t hrough QB5 stabilizes.Here transistor QB9 is t he key component . Itworks in t he forw
37、ard active region. The current flow2ing through QB9 ensures the large current outp ut abili2ty of V REF up to 1mA. In addition ,because QB9 is for2ward biased ,t he voltage on node A equals the referencevoltage plus V BE (forward2biased diode voltage drop ofQB9) . It is about 2V in t his design and
38、is power sup2ply2independent ,ensuring the circuit can be supplied bya wide voltage range.2. 3 Frequency compensationAs mentioned above ,t he amplifier used to stabilizet he reference voltage is as a three2stage amplifier , asshown in Fig15 ,and only the inner stage constit uted byQB6 and QB7 has a
39、positive Gm2 . Here ,t he point s A ,B ,and C correspond to t ho se in Fig14. In t his sit uation ,reversed nested Miller compensation ( RNMC) is t hemo st suitable approach 7 . Based on the Miller effect ,t he dominant pole p1 is related to the compensation ca2pacitor CC1 . Therefore ,the value of
40、CC1 determines t hesystem s stability. Here , nulling resistors are intro2duced to cancel t he R HP zero and to achieve a betterhigh2f requency dynamic range. More2over ,a proper re21351 1994-2010 China Academic Journal Electronic Publishing House. All rights reserved. http:/半 导 体 学 报 第 29 卷sistor l
41、oad at t he outp ut node can also reduce t he out2p ut impedance for better stability.3 Simulation and experimental resultsSimulations of the p roposed bandgap referencewere preformed in 115 m BCD technology. Figure 6shows t he simulated outp ut voltages of the two refer2ences , micro2power referenc
42、e , and supply2independentreference ,respectively ,when temperat ure sweep s from- 20 to 120 . Here , a supply voltage of 12V is ap2plied. The V REF1 of t he micro2power reference has amaximum drift of 3mV around t he mean outp ut volt2age of 11286V. The V REF of t he supply2independent ref2erence h
43、as a maximum drift of 117mV around t hemean outp ut voltage of 11276V.Figure 7 shows the simulated outp ut voltage ofpower supply2independent reference as a f unction oft he power supply voltage at 27 . The figure showst hat t he line regulation of 115 V/ V is achieved overt he supply voltage range
44、f rom 3 to 40V wit h a maxi2mum quiescent current of 80 A.Powered by a 12V supply , t he simulated PSRRcurve of the bandgap reference is shown in Fig18. Thecurve shows t hat the PSRR is higher t han 100dB forf requencies below 10k Hz.Fig. 8 Simulated PSRR of the bandgap voltage referenceFigure 9 sho
45、ws t he simulated outp ut voltage oft he bandgap reference as a f unction of the operatingcurrent when powered by a 12V supply. The V REF isnearly linear wit h t he operating current and t he maxi2mum variation is about 22mV.The bandgap circuit was fabricated in 115 m2p2m BCD technology. The chip p
46、hotograp h is shownin Fig110. The circuit area is 1180 m 434 m inclu2ding two trimming resistor arrays.The testing schemes are shown in Fig111.Adjusting t he supply voltage from 215 to 16V ,t hemeasured line regulation curve is plotted in Fig112.The curve is flat over a wide range of inp ut voltages
47、f rom 215 to 10V wit h a drift of about 300 V. A dra2matic change happens when V IN exceeds 10V. This isdue to the transistor breakdown under high voltages ,which is restricted by t he process. The working voltagecould extend to 40V if the proper high voltage processis available.Fig. 11 Testing sche
48、mes for line and load regulation2351 1994-2010 China Academic Journal Electronic Publishing House. All rights reserved. http:/第 8 期 Sun Yueming et al . : Design of a Bandgap Reference with a Wide Supply Voltage RangeThe load regulation was tested at a supply voltageof 8V. A microampere meter in seri
49、es wit h a load resis2tor RL is used to monitor t he current . By adjusting RL ,t he curve of V REF versus outp ut current is obtained , asshown in Fig113.For supply voltages between 215 and 10V ,t he testshows t hat the maximum quiescent current of t his ref2erence is 66 A in normal mode and 1015 A in sleepmode.Table 1 summarizes the reference specificationsobtained f rom simulation and measurement ,respective2ly.Tab
