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Consider the circuit shown above right. Here, you will use the following NMOS and PMOS models. You can import them into LTSpice a. Determine W2 such that an input DC level of 0.75 V yields an output DC level of 1 V. What is the low-frequency voltage gain under these conditions? Use AC analysis in SPICE to view the gain vs. frequency response of the amplifier. b. What is the change in the gain if the width and length of NMOS and PMOS devices varies by ±10% individually? Which one is the most sensitive? c. Establish a simulation setup to simulate the output resistance of the amplifier. What is the simulated value of the output resistance?

Consider the circuit shown above right. Here, you will use the following NMOS and PMOS models. You can import them into LTSpice a. Determine W2 such that an input DC level of 0.75 V yields an output DC level of 1 V. What is the low-frequency voltage gain under these conditions? Use AC analysis in SPICE to view the gain vs. frequency response of the amplifier. b. What is the change in the gain if the width and length of NMOS and PMOS devices varies by ±10% individually? Which one is the most sensitive? c. Establish a simulation setup to simulate the output resistance of the amplifier. What is the simulated value of the output resistance?

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Consider the circuit shown above right. Here, you will use the following NMOS and PMOS models. You can import them into LTSpice a. Determine W2 such that an input DC level of 0.75 V yields an output DC level of 1 V. What is the low-frequency voltage gain under these conditions? Use AC analysis in SPICE to view the gain vs. frequency response of the amplifier. b. What is the change in the gain if the width and length of NMOS and PMOS devices varies by ±10% individually? Which one is the most sensitive? c. Establish a simulation setup to simulate the output resistance of the amplifier. What is the simulated value of the output resistance?

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77. Consider the CS stage shown in Fig. 7.99, where M2 operates as a resistor. Figure 7.99 (a) Determine W2 such that an input dc level of 0.8 V yields an output dc level of 1 V. What is the voltage gain under these conditions? (b) What is the change in the gain if the mobility of the NMOS device varies by ±10% ? Can you explain this result using the expressions derived in Chapter 6 for the transconductance? In the following problems, unless otherwise stated, assume μnCox = 200 μA/V2, μpCox = 100 μA/V2, λ = 0, and VTH = 0.4 V for NMOS devices and −0.4 V for PMOS devices.

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Current Mirrors (35 points) This problem introduces current mirrors, which will be covered in more details in future lectures. Consider the circuit shown below (Figure 2). (W/L)1 = 1, (W/L)2 = 5, Rref = 50 kΩ, ignore channel length modulation unless otherwise stated. Assume L1 = L2 = 1 μm. Figure 2 a) (5 points) Assume RL = 10 kΩ. Calculate IL, the current flowing through RL. What is the current mirroring ratio ( IL over Iref , where Iref is the current through Rref )? We want the current mirror to provide a load-independent current as much as possible, so check that M2 is in saturation. b) (5 points) Determine the maximum RL and minimum VOut such that the current mirror still functions with the same current mirroring ratio you calculated in part a). Hint: for the current mirror to function as desired, transistor saturation should be maintained. c) (5 points) Channel length modulation introduces load-dependent errors in the mirroring ratio. Using λ = 0.1 V−1 for L = 1 μm, estimate the percentage error in the mirroring ratio. Here, set RL to its maximum value you got in part b ), and assume that we want the same IL as in parts a) and b). Hint: what should be the new VX and Iref ? d) (4 points) Compute the output resistance, Rout, , looking into the drain of M2. Use λ = 0.1 V−1 and assume the same IL as in parts a) through c). e) (5 points) Now consider redesigning the previous current mirror with source-degenerated transistors as shown in Figure 3. Ignore channel length modulation and body effect ( Assume bulk is tied to source). Transistor sizes remain the same, (WL)1 = 1 and (WL)2 = 5. This circuit has been designed to have the same Iref as in part a). What should the value of Rs2 be if we want the same current mirroring ratio as in a)? f) (5 points) Similarly to part b, determine the maximum RL and minimum VOut such that the current mirror still functions with the same current mirroring ratio as in part e). g) (4 points) Now compute the output resistance, Rout , looking into the drain of M2 (using λ = 0.1 V−1 ). Assume IL as used in parts e) and f ). h) (2 points) Comparing the minimum output voltage and the output resistance of these two current mirrors, comment on the advantages and disadvantages of using source degeneration in a current mirror. Figure 3 Current Mirrors (35 points) This problem introduces current mirrors, which will be covered in more details in future lectures. Consider the circuit shown below (Figure 2). (W/L)1 = 1, (W/L)2 = 5, Rref = 50 kΩ, ignore channel length modulation unless otherwise stated. Assume L1 = L2 = 1 μm. Figure 2 a) (5 points) Assume RL = 10 kΩ. Calculate IL, the current flowing through RL. What is the current mirroring ratio ( IL over Iref , where Iref is the current through Rref )? We want the current mirror to provide a load-independent current as much as possible, so check that M2 is in saturation. b) (5 points) Determine the maximum RL and minimum VOut such that the current mirror still functions with the same current mirroring ratio you calculated in part a). Hint: for the current mirror to function as desired, transistor saturation should be maintained. c) (5 points) Channel length modulation introduces load-dependent errors in the mirroring ratio. Using λ = 0.1 V−1 for L = 1 μm, estimate the percentage error in the mirroring ratio. Here, set RL to its maximum value you got in part b ), and assume that we want the same IL as in parts a) and b). Hint: what should be the new VX and Iref ? d) (4 points) Compute the output resistance, Rout, , looking into the drain of M2. Use λ = 0.1 V−1 and assume the same IL as in parts a) through c). e) (5 points) Now consider redesigning the previous current mirror with source-degenerated transistors as shown in Figure 3. Ignore channel length modulation and body effect ( Assume bulk is tied to source). Transistor sizes remain the same, (WL)1 = 1 and (WL)2 = 5. This circuit has been designed to have the same Iref as in part a). What should the value of Rs2 be if we want the same current mirroring ratio as in a)? f) (5 points) Similarly to part b, determine the maximum RL and minimum VOut such that the current mirror still functions with the same current mirroring ratio as in part e). g) (4 points) Now compute the output resistance, Rout , looking into the drain of M2 (using λ = 0.1 V−1 ). Assume IL as used in parts e) and f ). h) (2 points) Comparing the minimum output voltage and the output resistance of these two current mirrors, comment on the advantages and disadvantages of using source degeneration in a current mirror. Figure 3

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For all circuits, do not consider channel length modulation for calculating bias points. Unless otherwise specified, channel length modulation effect needs to be considered for small-signal analysis. All answers should be given to the second decimal place. Circuit and device parameters are: Vdd = 5 V;VTn = VTp = 1 V; μnCox = 50 μA/V2; μpCox = 25 μA/V2; λn = λp = 0.01 V−1; Lmin = 1 μm Figure 1 (for problems 1-3) Figure 2 (for problems 5-9) Figure 1: Transistor M1 has (W/L) = (160 μm/2 μm) and a bias current Iout = 2 mA. We desire M1 to be in saturation. You should assume λn = 0 for problems (1)-(3). Determine the ratio R1 /R2 required. 1 point Let VTn increase by 10% to 1.1 V. What is the new value of Iout in mA ? 1 point Let μnCox increase by 10% to 55 μA/V2. What is the new value of Iout in mA ? 1 point Figure 2: The circuit has Iref = 2 mA and Vp = 4 V. Transistors M1, M2 and M3 have (W/L) = (80 μm/1 μm). Determine the value of vx. (in volts) 1 point Determine the minimum allowable value of Vb (in volts) such that all devices are in saturation. 1 point Determine the maximum allowable value of Vb (in volts) such that all devices are in saturation. 1 point Determine Vb (in volts) such that vX = VY. 1 point determine the output resistance of this circuit ∂Vp/∂Iout in MΩ. 1 point Description for questions 9-10: An NMOS device with ID = 1 mA must operate in saturation with drain-source voltages as low as 0.5 V. The minimum required small-signal output impedance is 400 kQ. {Hint: You need to use the relations: rout = 1 /(λ⋅ID); λ⋅L = constant; and expression for VDS, sat = VGS−VT} Determine the length of the device in μm. 1 point Determine the width of the device in μm. 1 point

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