Comparison of bulk driven, floating gate and sub threshold methods in designing of a typical amplifier

Transcription

1 Journal of Novel Applied ciences Available online at 03 JNA Journal-03--9/ IN JNA Coparison of bulk driven, floatin ate and sub threshold ethods in desinin of a typical aplifier Abdullah Ahadi, ina Mohaadi, Mohaad Farahanchi and Abdolreza Esaeli 3*. Departent of Electrical Enineerin,MahoodAbaad University, MahoodAbaad, Iran. Departent of Electrical Enineerin, University of cience and echnoloy, Mazandaran-Babol, Iran 3. Plasa Physics and nuclear fusion research school, Nuclear cience and echnoloy Research Institute, ehran, Iran Correspondin author: Abdolreza Esaeli ABRAC: Nowadays one of the ost iportant paraeters in desinin analo circuits or even in the diital circuits is Reducin the consuption power of the circuit. In analo circuits, power consuption has a direct relationship with the values of circuit supply voltae and iven the equation in diital circuits the power can be directly related to the square of the supply voltae value. It is therefore concluded that the reduction of power consuption of analo or diital circuits can be achieved by reducin the supply voltae. Another advantae of low supply voltae is that circuits are easy to transport because the sall battery is used as the supply voltae on the. (e.., audio devices). Keywords: electronic aplifier, bulk driven, floatin ate, sub threshold, power consuption, low voltae supply, CMO, HPICE. INRODUCION In the industry it is tried to reduce the electronic tools size for easier access to the such as audio devices includin obile. One of the ways to reduce the volue is usin the low supply voltae. Because in doin so In addition to reducin the volue of the produced part, its power consuption will also be reduced. Althouh a reduced supply voltae is suitable to achieve this oal but there are liits to the threshold voltae of transistors and so that the supply value cannot be reduced. However, several ethods have been proposed throuh which one can achieve to a voltae ain and appropriate arin with inial supply voltae, aon the there are subthreshold, bulk-driven, floatin ate that each has strenths and pitfalls. in the paper it is tried to copare 3 ethods in order to deal with their strenths and pitfalls therefore a double floor circuit has been proposed which all entioned ethods have been used in order to desin it to reach a 35 db ain with 6 supply.then in the next sections we have tried to copare the results considerin briefly each ethod the intended circuit will be desined finally. Floatin ate MOFE Please Floatin ate MOFE has a structure siilar to a conventional MOFE. he only difference between the control ate and its substrate is that there is a poly silicon floatin ate which is surrounded by an insulatin silicon dioxide. (Blalock and Allen, 995; ai, 006). Gure. shows the structure of an N-channel floatin ate MOFE with two inputs &. he circuit analysis of this MOFE is siilar to an increental MOFE the only difference is that the inputs are connected to the transistor ate as capacitor connection. he sybol of the device is shown in Fiure. he capacitors & are sybol of fored capacitors between the floatin ate and input ates and is the capacitor between the floatin

2 ate and body. he perforance of the device is siilar to a conventional MOFE, which the only difference with the conventional MOFE is that the voltae on the ate is not directly controlled by the input control but the inputs can control the voltae on the ate via capacitors &.. he transistors can also work in active and sub-threshold area based on voltae relationship between ate and source and threshold voltae value. if transistor works in he active reion. ( ) c () c c0 c theq th c c C I v C 0 theq D FG C C k FG c th th c w v vt l QFG C DD C n C BB CGi i C D C B Gi n / C C Gi () (3) (4) (5) (6) However, if the transistor works in the active area, we will have the followin equation: and source and threshold voltae value.. Heq k I D (7) hus via a floatin ate transistor the total threshold voltae of the device can be lowered by applyin a DC voltae (Razavi, 00; Bahani and Fakhraie, 000). We'll di the threshold voltae by selectin values of the input capacitors even by selectin appropriately k and v we can reach the value th to zero. Its sall sinal odel is shown in Fiure. he capacitor between ate and drain causes the output ipedance of the transistor is reduced and the circuit ain died. (A) (B) Fiure. floatin-ate MOFE odel Fiure. all sinal odel of MOFE floatin ate C GD 0 f 0 C (8) 430

3 he transistor has various applications in the circuit.due to insulator between floatin ate the other nodes the load on it can be aintained for lon periods of tie. For this reason its iportant application is to ake EPROM and EEPROM eories in diital circuits. In analo circuits because the aount of threshold voltae of transistors can be controlled and reduced they are used in low voltae circuits. Input capacitance can cause an increase in circuit noise which is eliinated via suitable ethods. he ajor disadvantae of transistors is the hih cost durin construction. (Rosenfeld and Kozak, 004; Noran and Neff, 008; Yan and Andrrou, 009). A Brief tudy on the sub-threshold ethod When the ate - source voltae of a MOFE transistor is less than the threshold voltae, the Channel is in weak inversion which the area of the perforance is called sub-threshold transistor. Device consuption current in the reion is an exponential equation: I D r 0 I K " w l I D nk / q nk q e q( v G v tn ) exp nk (9) (0) () In this reion because the aount of transistors current is very low, circuit consuption power will below and also voltae drop on the drain - source terinal is low. Because of these two above iportant properties in desinin the low voltae and power circuits this structure is used. Nearly iilar to a transistor BJ, MOFE transistor trans-induction is directly related to the transistor current in the sub-threshold area (Rosenfeld and Kozak, 004) Because in the sub-threshold area there is low transistor current so the trans-induction value is low too. But iven the ain value is equal to, it is clear that the channel lenth plays an iportant role in the operation thus due to channel lenth increase the ain value will rise. But its weakness is that due to very low transistor current the trans-induction value of transistor is very sall, as a result the ain width and extent of circuit is reduced Because - for exaple - in a two-floor circuit, the value of circuit sinle ain width is directly related to the value of input floor trans-induction iven the equation (4). herefore, this type of circuit is used in the low frequency. GBW cc () In this ethod we ake use of the auxiliary and folded cascade circuit with it to strenthen further ain. his structure has pitfalls includin: It has no a ood frequency response. r For he values D 3k / q,the equations & 0 are non-linear and akes it difficult to desin. 3 o increase the ain of a transistor the devices width should be hih and so the speed of the circuit will be reduced. Investiation of body-driven circuits Dependency of the threshold voltae to the body voltae Usually the body terinal voltae in soe cases is naed as source of error. But the reality is that althouh the body terinal and the voltae on which and even the voltae deference between this terinal and especially the source terinal create soe probles in desinin and probably calculation and we should care about it as a second ate for this and even apply input sinal to it and expect the sinal aplification by the device in these conditions. Given that different discussions set forth for the arraneents with ate input (ate-driven) such as voltae aplification value, frequency response quality, input & output voltae liit, etc. It is necessary to adopt that whether the body can be as input, the above discussion should investiated. he chapter ais to learn ore about transistor circuits with sinal input to the body terinal (Bulk - Driven), and explorin soe iportant features of aplifier. 43

4 with respect to the threshold voltae relations in the devices PMO, NMO: bs H B ID ( B s ID G ( f B id h id h ) H )( ) B s (3) - ) NMO H th0 ( f B f ) PMO (4) I D C n ox w ( l G th ) (5) It can be seen that the rate of voltae chanes of body-source ay ipact on the threshold voltae. For exaple, as shown in Fiure 3 due to increase of the body terinal voltae in relation to the source, threshold voltae is reduced. hus, iven the drain current relationship with threshold voltae reduction the drain current increases. Another point is presuable fro equations (5),(6) and (7) is that the rate of chanes of transistors current is less than that of body-source voltae in coparison to that of source-ate voltae, o when the devices are bein used up by the body-driven ethod they have ore input chanes than ate driven state. he quality of the above entioned atter is shown in Fiure 3. Accordin to Fiure 3 in a transistor, n-type increases due to increase in the body voltae relative to the transistor current source. But what is iportant is that the body terinal voltae value should also be liited because pad lock or leakae current throuh device internal diodes will effect on the transistor function. If the input voltae of the body (in the device NMO) increases, internal bonds PN between the body and source and that of the drain and body source will becoe active and even activates the links (Fiure 4). In addition unwanted BJ transistors ay be activated and pad lockin happen. Fiure 3. the drain current with respect to body-source and ate - source voltae Fiure 4. internal structure of an NMO 43

5 In DC analysis of transistor circuit, the drain current can be calculated via followin equation reardless of any arraneent. w ID 0Cox G H0 f B f l (6) Which the followin equations are defined in: aturation reion D G H (7) riode reion D G H (8) Cut-off reion G H (9) o the DC voltae of body - source terinal has a feature either in circuits(bulk-driven) or in circuits (Gate- Driven) and will chane the operatin point to the sae extent.in all-sinal analysis of a device as body-driven or with ate input or observin sall sinal odel of the aplifiers we will have the followin equations. Latch up: bs bs B s ID H G f f ID ( B ( B (0) () () 0. x 0.4 (3) id h B id h ) s H )( ) B B f (4) In he sall-sinal analysis, the drain current in addition to dependency on the ate - source sall sinal voltae ( s ) is depended as well to the Body - source sall-sinal voltae that the dependency value and bs is f defined via trans-inductions & which in the equations described if B , bs is ore than, but the pitfall of this is the hih leakae current and probably the pad lockin Relations (Philllip, 003). As it has been shown in the above equations bs, this eans that the trans-induction value could even be five bs ties larer than that of trans-induction.i.e. he value of the sinal strenth by insertin the input into the body is 5 ties lower than sinal insertion into the ate, and then it is also the weakness of body-driven circuit. Another weakness with the body input is its speed reduction relative to the oent the sae device works with input ate frae (Pease Robert, 000). ft f bulkdriven t 3. 8 atedriven (5) Coparison of ethods Fiures 5,6 and 7 are respectively the circuits with quite siilar structure which their differences are: how to insert the input voltae to the circuit, how to bias and also kind of input transistor. he circuit K in the first floor is a PMO differential double floor circuit that was used. he second floor circuit is a low voltae aplification AB. a voltae source was used to bias the second floor circuit. We exaine 3 paraeters such as size,phase arin and consuption power to copare the ethods for 433

6 achievin the voltae ain in 35 db. Fiure 5- shows the circuit with differential pair input in the body-driven layout. Fiure 5. he circuit with body-driven input able. ize of circuit transistors and eleents in fiure 5 L(µ) W(µ) eleents ize M CL 5p M.7 R 0.k M.7 C 0n M3 4.8 A 35db M4 8 PH 75 M5 P(w) 946n M5 eleents ize M7 7 Fiure 6. Frequency response of the circuit in Fiure 5 Fiure 7. the proposed circuit which all devices are biased in sub-threshold reion able. he transistors and eleents size of the circuit in Fiure 7 M L(µ) W(µ) M 0 70 M 0 70 M3 70 M4 60 M5 40 M eleents ize CL 5p C.3p R 00K A 35db PH 30 P(w) 6n 434

7 Fiure 8. Frequency response of the circuit in Fiure 7 Fiure 9. Circuit with floatin ate input We will discuss the circuit via floatin ate transistor inputs. able 3. ize of the transistors and eleents of circuit in Fiure 9 M L(µ) W(µ) eleents ize M 5 CL 5p M 5 C f M3.5 R 0.5K M4 A 35db M5 5 PH 8 M5 5 P(w).97u M7 5 Fiure 0. Frequency response of the circuit in Fiure 9 It can be seen that in Coparison of phase arin and circuit size (occupied space) the body driven is ore preferred and the sub-threshold ethod will occupy ore volue. In coparison of power consuption three ethods are perceived. he sub-threshold ethod has less consuption power in proportion to two other ethods and the floatin-ate ethod will have ore consuption power. 435

8 CONCULION In the paper after desinin a double floor circuit by 3 ethods which has been carried out throuh 6 supply voltae; it was evident that even if all of the can be used in low supply voltae very well but dependin on the overall oal everyone can be used. For exaple, if circuit desin taret is led to very low consuption power the sub-threshold technique is the ost appropriate one However; its low frequency response still reains as before or if the objective of circuit desin is with a suitable volue of bulk. REFERENCE Bahani and Fakhraie M A Rail o Rail Constant G -olt cosopap proceedin of the IEEE international syposiu on circuit and syste,ol., PP Blalock B J and Allen PE A low-voltae,bulk-driven MOFE current Mirror for CMO echnoloy IEEEInternational yposio on Circuit and yste,ica95.,ol.3, PP B Kin Fahd university of petroleu and Minerals "Ultera-Lowoltae Operational plifier". Noran L, Neff J "A Novel Floatin Gate Circuit Faily with ubthreshold oltae win Ultra Low Power operation" International conference.on circuit and yste Dec, pp.-6. Pease R "he Desin Of Band- ap circuits"ieee 990 Bipolar and circuitechnoloy Meetin,PP 4-8. Philllip E Allen Benjain J.Blalock scool of electrical and coputer enineerin Georia institute of technoloy Atlanta"Low voltae analo circuits usin standards Cos technoloy". Rairez J "Low upply oltae Ota Artitecture Usin Floatin Gate ransistors"ieee Electrical and coputer enineerin. Razavi B. 00. Desin of Analo CMO Interated circuits New York:Mc Graw-Hill. Rosenfeld J and Kozak M A Bulk-Driven CMO OA with 68db DC Gain, th IEEE International conference.on circuit and yste,icec 004,dec,pp.5-8. ai C F Usin Bulk-Driven echnoloy Operate In subthreshold to Reion to Desin alow oltaeand Operatoinal Aplifier IEEE Circuit and yste. pp Yan K and Andrrou G "he Multiple Input Floatin Gate MO Difrential Aplifier An Analo oputational Buildin Block" IEEE Circuit and yste pp