ECEN326: Electronic Circuits Fall 2017

Transcription

1 CN326: lectonic Cicuits Fall 2017 Lectue 6: Opeational Tansconductance Aplifies (OTAs) Sa Paleo Analo & Mixed-Sinal Cente Texas A&M Uniesity

2 Announceents HW4 due today HW5 due 11/1 2

3 OpAps and OTAs OpAp OTA Hih oltae ain Hih input ipedance Voltae souce output (low ipedance) Hih oltae ain Hih input ipedance Cuent souce output (hih ipedance) 3

4 Siple OTA Ipotant Paaetes Tansconductance Output esistance Diffeential Gain Coon-Mode Input ane 4

5 Siple OTA Tansconductance: ioous Analysis A 1 3 The 1 3 O3 ON in1 in2 and The 2 i ON p 4A in1 in2 2 To find isc, we need to find ip and in ON in1 in2 i O3 2 ON Fo Lectue 3 i 4 p ON in1 A in2 2 3 in1 in2 n i 2 sc ON i G p 1 i 3 n in1 isc in2 in1 2 in2 in1 in2 5

6 Siple OTA Tansconductance: Infoal Vitual Gound Appoach As the diffeential cicuit is not puely syetic, we cannot foally assue a itual ound at node P Howee, if the diffeential pai tansistos M1 and M2 hae hih output esistance, a itual ound can be appoxiated at node P to siplify the analysis G i sc in1 i p isc i in2 i i n n p in1 in1 in2 Assuin an ideal cuent io load in1 in1 2 in2 2 in2 in2 6

7 Siple OTA Output esistance G out out It is often useful to also use the output conductance 1 out Op On op on 7

8 Siple OTA Diffeential Gain A G A out On Op op On on Op 8

9 Siple OTA Coon-Mode Input ane Coon-ode input ane set by tansisto satuation conditions Low-end set by tail cuent souce satuation V ic V DSAT 5 Hih-end set by diffeential pai satuation V ic V oc 2I C n V ox SS W L V GS1 n 2I C SS TH, n1 VDD VGS3 VTH, n1 VDD VTH, p3 VTH, n1 W pc ox L 3 5 n I C SS ox W L 1 V TH, n1 V ic V DD I C p I SS ox W L ox 3 SS W L 5 V TH, p5 C n I SS ox V W L 1 TH, n1 V TH, n1 9

10 Bipola Siple OTA Followin a siila pocedue A G out On Op On Op on op Low-end V ic set by keepin tail cuent souce in actie ode Vic VC, sat VB, on 0.3V 0.7V 1V Hih-end V ic set by keepin diffeential pai in actie ode V V V V V V C1 V CC ic V B, on CC V ic C, sat V B, on CC 0.3V C, sat 10

11 3 Cuent Mio OTA BI TAIL 2 MN B : 1 MP V- I V+ M1 M1 I TAIL 1 : B 1 : 1 i o O G sc i sc While G has inceased by the cuent io facto B, the oltae ain eains the sae due to the output esistance bein educed by B -1 i i p out i i p i n n B B B B B G out A Op B 1 1 B O1 1 B op Op B B O1 1 Op o1 1 O1 B 1 Coon-ode input ane expession eains the sae as the peious siple OTA 11

12 Bipola 3 Cuent Mio OTA w/ Deeneated G (Lab 7) In ode to ipoe the distotion pefoance, eitte esistos hae been added in the input diffeential pai In ode to ipoe the output esistance, eitte esistance has been added to all the cuent io/souce tansistos G Assuin a 1:1atio fo all the cuent ios, is set by the deneated G of the input tansistos 1 G e1 1 e1 1 12

13 Bipola 3 Cuent Mio OTA w/ Deeneated G (Lab 7) ,, e e e e o o o o out

14 Bipola 3 Cuent Mio OTA w/ Deeneated G (Lab 7) Maxiu diffeential input ap. fo ood distotion V id 1 2 e1 1 Low-end V ic set by keepin tail cuent souce in actie ode T V ic V IT B3 VC, sat 1 VB, on Hih-end V ic set by keepin diffeential pai in actie ode C1 V CC IT 2 V ic 2 V V CC B, on IT 2 V 2 ic V I 2 V C, sat B, on V C, sat I id, ax T 1 14

15 Siulatin the 3 Cuent Mio OTA To siulate diffeential aplifies, use oltae-contolled oltae souces (VCVS o eleents) to eneate the diffeential input sinal and onito the cuent thouh the load esisto Note: This exaple is desined fo 2X the Lab 7 G Sinle-ended input souce Monito I(L) DC oltae souce to set input DC leel 2 VCVS to eneate diffeential inputs 15

16 Siulatin Tansconductance Set Inputs 1 Gain=0.5 and 2 Gain=-0.5 With input souce AC=1, siply plot the load esisto cuent I(L) to et the tansconductance Monito I(L) Sinle-ended input souce DC=0 AC=1 DC oltae souce to set input DC leel Gain=0.5 Gain=

17 Siulatin Tansconductance G = 2.01A/V 17

18 Siulatin Diffeential ind The diffeential input esistance is equialent to the diffeential input (Vi) diided by the input cuent, whee I use the base cuent of Q1 o IB(Q1) ind = 159k 18

19 Siulatin THD Set input souce to diffeential input aplitude spec Fo Lab 7, that is 2V Check the THD at 3 diffeent coon-ode points 0V, V CM,in, V CM,ax V CM =0V V CM =-2V V CM =2V 19

20 Siulatin Output esistance Gound input souce and apply an AC-coupled oltae stiulus at output With output souce AC=1, plot the atio of V(Vout) oe the cuent thouh the couplin capacito Output stiulus Gound input souce 20

21 Siulatin o The output esistance is equialent to the output stiulus V(Vout) diided by the output cuent, which is equal to the cuent thouh the output capacito I(C5) o = 25.4k 21