REPASO EXAMEN 2 INEL 4207 - Fall 2012
Monday, October 1, 12 SUBJECTS
• Pass-transistor Logic / Transmission gates
• Dynamic / Domino Logic
• Emitter-coupled Logic
• BiCMOS
Monday, October 1, 12 SOURCES • Textbook’s 5th ed.:
◦ PTL: 10.5 ◦ Dynamic/Domino Logic: 10.6 ◦ ECL: 11.7 ◦ BiCMOS: 11.8
• 6th Ed.: chapter 15th (int’l), 14th (USA) sections 2 to 5.
• Slides and examples on courses’ web page
• Your lecture notes
• Practice problems: 1, 2, 5, 6, 8-10, 12-14, 17, 21, 24-27, 30, 35, 36 & 39
Monday, October 1, 12 Pass-Transistor Logic
Figure 15.5 Conceptual pass-transistor logic gates. (a) Two switches, controlled by the input variables B and C, when connected in series in the path between the input node to which an input variable A is applied and the output node (with an implied load to ground) realize the function Y = ABC. (b) When the two switches are connected in parallel, the function realized is Y = A(B + C).
Monday, October 1, 12 Figure 15.6 Two possible implementations of a voltage-controlled switch connecting nodes A and Y: (a) single NMOS transistor and (b) CMOS transmission gate.
Monday, October 1, 12 Figure 15.7 A basic design requirement of PTL circuits is that every node have, at all times, a low resistance path to either ground or VDD. Such a path does not exist in (a) when B is low and S1 is open. It is provided in (b) through switch S2.
Monday, October 1, 12 For NMOS switch, load capacitor charges to vC - Vt Body effect -> Vt
Figure 15.8
Monday, October 1, 12 NMOS switch discharges capacitor completely
Monday, October 1, 12 For PMOS switch, C charges to vC and discharges to Vt
Monday, October 1, 12 Example Consider the NMOS switch shown in figs. 15.8 and 15.9 for which µnCox = 2 2 50µA/V , µpCox = 20µA/V , Vt0 =1V , =0.5 V ,2⇥f =0.6V and VDD = 5V . Let the transistor have W/L| =4| µm/2µm, and assume C = 50fF.
1. For vi high, (fig. 15.8) find VOH.
2. If the output feeds a CMOS inverter whose (W/L)p =2.5(W/L)n = 10µm/2µm, find the static current in the inverter and its power dissi- pation when its input is the value found in (1). Find the inverter output voltage.
3. Find tPLH.
4. Find tPHL for the case with vi going low (fig. 15.9).
5. Find tp.
Monday, October 1, 12 CMOS switch - C charges to vC and discharges to 0
Figure 15.11 The CMOS transmission gate and its circuit symbol.
Monday, October 1, 12 Figure 15.12
Monday, October 1, 12 Transmission gate resistance empirical for- mula (for submicron technologies) (eq. 15.36) 12.5 RTG = k (W/L)n
Monday, October 1, 12 Figure 15.14 (a) A transmission gate connects the output of a CMOS inverter to the input of another. (b) Equivalent circuit for the purpose of analyzing the propagation delay of the circuit in (a).
Monday, October 1, 12 Elmore delay formula (eq. 15.37):
tp =0.69 [C1R1 + C2 (R1 + R2)+C3 (R1 + R2 + R3)]
Figure 15.15 A three-section RC ladder network.
Monday, October 1, 12 Figure 15.16 Realization of a two-to-one multiplexer using pass-transistor logic.
Monday, October 1, 12 Figure 15.17 Realization of the XOR function using pass-transistor logic.
Monday, October 1, 12 Figure 15.18 An example of a pass-transistor logic gate utilizing both the input variables and their complements. This type of circuit is therefore known as complementary pass-transistor logic, or CPL. Note that both the output function and its complement are generated.
Monday, October 1, 12 Dynamic / Domino Logic
Figure 15.19 (a) Basic structure of dynamic-MOS logic circuits. (b) Waveform of the clock needed to operate the dynamic logic circuit. (c) An example circuit.
Monday, October 1, 12 Figure 15.20 Circuits for Example.
2 Assume VDD =1.8V , Vt =0.5V , µnCox =4µpCox =0.3mA/V ,(W/L)n = 0.27µm/0.18µm (including Qe), (W/L)p =0.54µm/0.18µm (for Qp), CL = 20fF.
a) For the pre-charge operation, with Qp’s gate at 0V and if CL is fully discharged at t = 0, find the time for vY to rise from 10% to 90% of VDD.
b) For A = B = C = D = 1, find tPHL
Monday, October 1, 12 Figure 15.21 (a) Charge sharing. (b) Adding a permanently turned-on transistor QL solves the charge sharing problem at the expense of static power dissipation.
Monday, October 1, 12 Cascading dynamic logic gates
By the time vY1 drops to Vt, CL2 can loose a significant amount of charge causing vY2 to can be significantly reduced.
Figure E 15.10
Figure 15.22 Two single-input dynamic logic gates connected in cascade. With the input A high, during the evaluation phase CL2 will partially discharge and the output at Y2 will fall lower than VDD, which can cause logic malfunction.
Monday, October 1, 12 Consider the circuit as the evaluation phase begins: at t = 0, vY 1 = vY 2 = VDD and v = vA = VDD. Qp1 and Qp2 are cuto⇥ and can be removed from the equivalent circuit. Replace series combinations of Q1 Qe1 and Q2 Qe2 by equivalent devices. Consider the interval t during which vY 1 falls from VDD to Vt, at which time Qeq2 turns o⇥ and CL2 stops discharging. Assume (W/L)n =4µm/2µm and CL1 = CL2 = 40fF. Assume VDD =5V , Vt0 =1V , µnCox =2.5µpCox = 2 50µA/V ,(W/L)n =4µm/2µm. Find
a) (W/L)eq1 and (W/L)eq2.
b) an average iD1, iD1,av, from iD1(vY 1 = VDD) and iD1(vY 1 = Vt).
c) t using iD1,av
d) iD2,av obtained when vY 1 is halfway through its excursion (i.e. vY 1 =3V ). Hint: Qeq2 is in saturation.
e) Use t found in (c) and iD2,av to estimate the reduction in vY 2 and its final value.
Monday, October 1, 12 Figure E 15.10
Monday, October 1, 12 Figure 15.23 The Domino CMOS logic gate. The circuit consists of a dynamic-MOS logic gate with a static-CMOS inverter connected to the output. During evaluation, Y either will remain low (at 0 V) or will make one 0-to-1 transition (to VDD).
Monday, October 1, 12 Figure 15.24 (a) Two single-input Domino CMOS logic gates connected in cascade. (b) Waveforms during the evaluation phase.
Monday, October 1, 12 ECL
Figure 15.25 The basic element of ECL is the differential pair. Here, VR is a reference voltage.
Monday, October 1, 12 Figure E15.12
Monday, October 1, 12 Figure 15.26 Basic circuit of the ECL 10K logic-gate family.
Monday, October 1, 12 Figure 15.27 The proper way to connect high-speed logic gates such as ECL. Properly terminating the transmission line connecting the two gates eliminates the “ringing” that would otherwise corrupt the logic signals. (See Section 15.4.6.)
Monday, October 1, 12 Figure 15.28 Simplified version of the ECL gate for the purpose of finding transfer characteristics.
Monday, October 1, 12 Monday, October 1, 12 Figure 15.30 Circuit for determining VOH.
Monday, October 1, 12 fig. 15.32 (international, 6th edition)
Monday, October 1, 12 Figure 15.36 The wired-OR capability of ECL.
Monday, October 1, 12 Name: INEL4207 Digital Electronics - A2
Student #: Sec.: December 21, 2010
This exam has 3 problems. Each problem counts for 1/3 of the exam grade.
1. For the ECL inverter shown in the following sketch, the high voltage level is V = 1.7V and H − the average power dissipated when the input is high 50 % of the time is P =5mW .Determine the source’s current IEE,thelowvoltagelevelVL,thereferencevoltagelevelVREF and the value of resistance R3.
2k
2k
Q3
vin vout Q1 Q2 VREF
R3
IEE -3.3V -5.2V
Monday, October 1, 12 2. El siguiente diagrama muestra una red de transmisi´on:
+5V +5V +5V c +5V ab
CL
2 Los parametros son: VT 0 =0.75V , γ =0.55√V ,2φF =0.6V ,yKn =100µA/V .
a)(15puntos)Determineelvoltajeenlosnodosa, b,yc si se desprecia el body effect. b)(20puntos)Repitalaparte(a)tomandoencuentael ”body effect.”Debe analizar el circuito y mostrar el procedimiento que conduce al resultado.
Monday, October 1, 12 Name: Student number:
2. Find VL, VH and VREF for the following circuit. Neglect base currents and assume VBE =0.7V if a transistor is ON. (25 points)
1kΩ
Q2
vIN Q1 VREF vOUT
1kΩ 4kΩ
-2V -5V
Monday, October 1, 12 BiCMOS
Figure 15.37 Development of the BiCMOS inverter circuit. (a) The basic concept is to use an additional bipolar transistor to increase the output current drive of each of QN and QP of the CMOS inverter. (b) The circuit in (a) can be thought of as utilizing these composite devices. (c) To reduce the turn-off times of Q1 and Q2, “bleeder resistors” R1 and R2 are added. (d) Implementation of the circuit in (c) using NMOS transistors to realize the resistors. (e) An improved version of the circuit in (c) obtained by connecting the lower end of R1 to the output node.
Monday, October 1, 12 Figure 15.38 Equivalent circuits for charging and discharging a load capacitance C. Note that C includes all the capacitances present at the output node.
Monday, October 1, 12 Figure 15.39 A BiCMOS two-input NAND gate.
Monday, October 1, 12 The diagram shows the charging of a load capacitance C by the pull-up section of a BiCMOS.
Find tPLH (the time it takes vO to reach VDD/2 if the cap is initially discharged) if VDD = 5V, vbe 2 = 0.7V, kP = 100 µA/V , C = 1pF and R1 = 20kΩ.
Monday, October 1, 12 The diagram shows the charging of a load capacitance C by the pull-up section of a BiCMOS.
Find tPLH (the time it takes vO to reach VDD/2 if the cap is initially discharged) if VDD = 5V, vbe 2 = 0.7V, kP = 100 µA/V , C = 1pF and R1 = 20kΩ.
i = iE + iR1 i =( + 1) (i i )+i D R1 R1 =( + 1)i i D R1 dv i = C O dt
The average current method can be used to estimate tPLH.
Monday, October 1, 12