ES 330 Electronics II Homework # 8 Soltuions (Fall 2017 Due Wednesday, November 13, 2017)

Transcription

1 Page1 Name Solutions ES 330 Electronics Homework # 8 Soltuions (Fall 017 ue Wednesday, November 13, 017) Problem 1 (16 points) You are given a common-emitter BJT and a common-source MSFET (n-channel). Fill in the table below. ssume the BJT to be in the forward active mode and the n- channel MSFET to be in the saturation region of operation. [The purpose of this exercise is to compare BJT and MSFET parameters. Remember that 0 is the voltage gain without a separate load resistance RL.] NPN BJT Cell = 100, = 100 and TH = kt/q = 5 millivolt N-channel MSFET Cell ncx = 00 /, (W/L) = 40 and = 10 Bias Current is C = 0.1 m C = 1 m = 0.1 m = 1 m gm (m/) r0 (k) (/) RN (k) 5.5 Equations: For the BJT: g ; r ; g r ; R r C m 0 m 0 in TH C gm For the MSFET: g C 4 L mi n X i i i ' L 40 r0i ; gmir0i ; Rin i i m ;

2 Page Problem (0 points) You are given the circuit drawn below. t is fabricated in a CMS process for which ncx = pcx = 00 /, n = p = 0 /m, tn = -tp = 0.5 volt and =.5 volts. The two transitor types have L = 0.5 m and are to be operated at = 0.1 m and = 0.3 volt. Find the required gate node voltage G applied to Q and the (W/L) ratios for both the n-channel and p-channel MSFETs to meet the stated conditions. [The subscripts n and p denote n-channel and p-channel, respectfully.] Note: 0.1 m 100 μ is specified as the operating current and SG tp G SG 1 W 1 W W 1 1 nc X (0.3) 11.1 L L L 1 W C L p X p n n n 1 W W (0.3). L L gm1 r01 r0 and gm r ' L r 100 k ; therefore, p m p G = _1.7_ volts (W/L)n = _11.1_ and (W/L)p = _._

3 Page3 Problem 3 (14 points) The schematic below shows a cascoded n-channel MSFET pair used to achieve higher output resistance RUT. We want to achieve RUT = 00 k using this cascode pair operating at a drain current = 0.5 m. ssuming identical geometrical device layouts, so that (W/L)1 = (W/L) = (W/L), ncx = 0.1 m/volt, and = 10 volts; what is the required gate width-to-length ratio (W/L) for this circuit? R g r r UT m must equal 00 k is given. 10 r0 0,000 ohms (0.0005) We know that r r r ,000 g (0,000) ; hence, g.0005 m1 m1 m Using gm1 nc X ; (0.0001) L L Solving for W/L gives,.5 L

4 Page4 Problem 4 (10 points) n a MSFET cascode amplifier we want the transistor performing the cascoding function to increase the output resistance by a factor of 50. Reference: See Figure 8.30 on page 548. (a) f the cascoding transistor is operated at = 0. volt, what must the value of the Early voltage be to accomplish this? For a MSFET: g ; r ; m 0 For a cascode MSFET the multiplying factor K for the resistance step up we have Equation (8.7) gives 50 5 volts K g r m 0 (b) f the process technology specifies as 5 /m, what channel length L must the transistor have? ' ' μm 5 volts = L and for 5 implies L 1 μm Problem 5 (0 points) Given the cascoded current source as shown in the figure:

5 Page5 (a) Show that if the two transistors are identical, the current supplied by the current source, and the output resistance R0 are related bythe expression, R0 = /. For a MSFET cascoded current source: gm ; The output resistance R R g r r R R m (Fig on page 550) is ssuming identical FET devices, as was to be shown. for both NMS (b) Next, consider the case of transistors having = 4 volts and operated at = 0. volt. lso, let ncx = 100 /. Find the W/L ratios required and the output resistance realized for different two currents: (1) = 0.1 m and () = 0.5 m. ssume that S for both devices is the minimum voltage required, that is, S =. r0 and PMS. Given = 4, = 0. and C = 0.1 μ/ n X 0.1 For case (1), = 0.1 m; gm 1 m/ 0. 4 r0 40 k ; R gm( r0) 0.001(40000) 1.6 M 0.1 C L L g m Using m n X 50 L 0.5 For case (), = 0.5 m; so gm 5 m/ 0. 4 r0 8 k ; R gm( r0) (8000) 30 k 0.5 m Using L L

6 Page6 Problem 6 (0 points) Consider the cascoded amplifier shown schematically below. t is operated at a current = 0. m with all devices operating at = 0.0 volt. ll four devices have = 4 volts. Find gm1, the output resistance of the amplifier Ro,n, the output resistance of the current source Ro,p and the voltage gain. Given: 0. m; 0. volt; 4 volts We want to find g, R, R and. m1 (0.) 0. m1 o, p o, n ll four devices are identical (same g and r for each). g m 4 r0 0 k and Ro, n Ro, p ( g mr0) r0 0. R R ( ) 800 k o, n o, p and R ( R R ) 400 k o, n o, p g R 0.00(400000) 800 m m 0