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# Category: buliding blocks of integrated circuit amplifiers chaptet 8 sedra and smith

# **8.101 In each of the six circuits in Fig. P8.101, let β = 100, and neglect ro. Calculate the overall voltage gain

# 8.100 Consider the CD–CG amplifier of Fig. 8.48(c) for the case gm = 5 mA/V, Rsig = 500 k, and RL = 10 k. Neglecting ro, find Gv.

# 8.99 For the amplifier in Fig. 8.48(a), let I = 0.5 mA and β = 100, and neglect ro. Assume that a load resistance of 10 k is connected to the output terminal. If the amplifier is fed with a signal vsig having a source resistance Rsig = 10 k, find G v.

# 8.98 The BJTs in the Darlington follower of Fig. P8.98 have β = 100. If the follower is fed with a source having a 100-k resistance and is loaded with 1 k, find the input resistance and the output resistance (excluding the load). Also find the overall voltage gain, both open-circuited and with load. Neglect the Early effect.

# D *8.97 Consider the BiCMOS amplifier shown in Fig. P8.97. The BJT has VBE = 0.7 V and β = 200. The MOSFET has V t = 1 V and kn = 2 mA/V2. Neglect the Early effect in both devices (a) Consider the dc bias circuit. Neglect the base current in Q2 in determining the current in Q1. Find the dc bias currents in Q1 and Q2 and show that they are approximately 100 μA and 1 mA, respectively. (b) Evaluate the small-signal parameters of Q1 and Q2 at their bias points. (c) Determine the voltage gain Av = vo/vi. For this purpose you can neglect RG. (d) Noting that RG is connected between the input node where the voltage is vi and the output node where the voltage is Avvi, find Rin and hence the overall voltage gain vo/vsig. (e) To considerably reduce the effect of RG on Rin and hence on G v, consider the effect of adding another 10 -M resistor in series with the existing one and placing a large bypass capacitor between their joint node and ground. What will R in and Gv become?

# 8.96 The transistors in the circuit of Fig. P8.96 have β = 100 and V A = 50 V. (a) Find Rin and the overall voltage gain. (b) What is the effect of increasing the bias currents by a factor of 10 on R in, Gv, and the power dissipation?

# 8.95 A source follower for which k n = 200 μA/V2, VA = 20 V/μm, χ = 0.2, L = 0.5 μm, W = 20 μm, and Vt = 0.6 V is required to provide a dc level shift (between input and output of 0.9 V.) What must the bias current be? Find gm, gmb, ro, Avo, and Ro. Assume that the bias current source has an output resistance equal to ro. Also find the voltage gain when a load resistance of 2 k is connected to the output

# 8.94 Use the source-follower equivalent circuit in Fig. 8.45(b) to show that its output resistance is given by R o = ro3ro1 1 gm +gmb 1 gm +gmb

# D 8.93 If the pnp transistor in the circuit of Fig. P8.93 is characterized by its exponential relationship with a scale current I S, show that the dc current I is determined by IR = V T ln(I/IS). Assume Q1 and Q2 to be matched and Q3, Q4, and Q5 to be matched. Find the value of R that yields a current I = 200 μA. For the BJT, VEB = 0.7 V at I E = 1 mA

# D 8.92 (a) For the circuit in Fig. P8.92, assume BJTs with high β and vBE = 0.7 V at 1 mA. Find the value of R that will result in I O = 10 μA. (b) For the design in (a), find Ro assuming β = 100 and VA = 40 V.

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