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Example 3: A shunt-shunt feedback amplifier is shown in Figure EX3. Assume the following specifications: gm = 40 mA/V RF = 33 kΩ rπ = 4 kΩ ro = ∞ (a) Determine the A-circuit. (b) Determine the input resistance Ri, the output resistance Ro, and the open-loop transresistance (A) of the A-circuit. (c) Determine the feedback factor β = If/Vo and the closed-loop gain Af. (d) Determine the input and output resistance of the feedback amplifier Rif and Rof, respectively. (e) Determine Rin and Rout . Figure EX2

Example 3: A shunt-shunt feedback amplifier is shown in Figure EX3. Assume the following specifications: gm = 40 mA/V RF = 33 kΩ rπ = 4 kΩ ro = ∞ (a) Determine the A-circuit. (b) Determine the input resistance Ri, the output resistance Ro, and the open-loop transresistance (A) of the A-circuit. (c) Determine the feedback factor β = If/Vo and the closed-loop gain Af. (d) Determine the input and output resistance of the feedback amplifier Rif and Rof, respectively. (e) Determine Rin and Rout . Figure EX2

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Example 3: A shunt-shunt feedback amplifier is shown in Figure EX3. Assume the following specifications:
g m = 40 m A / V R F = 33 k Ω r π = 4 k Ω r o = ∞
(a) Determine the A-circuit. (b) Determine the input resistance R i , the output resistance R o , and the open-loop transresistance ( A ) of the A-circuit. (c) Determine the feedback factor β = I f / V o and the closed-loop gain A f . (d) Determine the input and output resistance of the feedback amplifier R i f and R o f , respectively. (e) Determine R in and R out . Figure EX2

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In the amplifier circuit, given VCC = 10 V, R1 = 160 kΩ, R2 = 40 kΩ, RC = 2 kΩ, and RL = 2 kΩ, answer the following questions. Assume the BJT has a β = 100. (a) Calculate RE to make the BJT's operating point (Q-point) current ICQ = 2 mA. (b) Assuming ro = ∞ and CE = ∞, draw the small-signal equivalent circuit of the amplifier and calculate the amplifier's input resistance (Rin), output resistance (Rout), and voltage gain (Av). (c) Assuming ro = ∞ and CE = 0, draw the small-signal equivalent circuit of the amplifier and derive the expression for the voltage gain (Av). Then, calculate the value of Av. (d) Assuming ro = 10 kΩ and CE = 0, draw the small-signal equivalent circuit of the amplifier and derive the expressions for Rin , Rout , and Av. Then, calculate their values. (e) To operate as an amplifier, in which operating region should the BJT be biased? Explain the reason with the help of the voltage transfer characteristic.In the amplifier circuit, given VCC = 10 V, R1 = 160 kΩ, R2 = 40 kΩ, RC = 2 kΩ, and RL = 2 kΩ, answer the following questions. Assume the BJT has a β = 100. (a) Calculate RE to make the BJT's operating point (Q-point) current ICQ = 2 mA. (b) Assuming ro = ∞ and CE = ∞, draw the small-signal equivalent circuit of the amplifier and calculate the amplifier's input resistance (Rin), output resistance (Rout), and voltage gain (Av). (c) Assuming ro = ∞ and CE = 0, draw the small-signal equivalent circuit of the amplifier and derive the expression for the voltage gain (Av). Then, calculate the value of Av. (d) Assuming ro = 10 kΩ and CE = 0, draw the small-signal equivalent circuit of the amplifier and derive the expressions for Rin , Rout , and Av. Then, calculate their values. (e) To operate as an amplifier, in which operating region should the BJT be biased? Explain the reason with the help of the voltage transfer characteristic.
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11.65 The feedback transresistance amplifier in Fig. P11.65 utilizes two identical MOSFETs biased by ideal current sources I = 0.4 mA. The MOSFETs are sized to operate at VOV = 0.2 V and have Vt = 0.5 V and VA = 16 V. The feedback resistance RF = 10 kΩ. (a) If Is has a zero dc component, find the dc voltage at the input, at the drain of Q1, and at the output. (b) Find gm and ro of Q1 and Q2. (c) Provide the A circuit and derive an expression for A in terms of gm1, ro1, gm2, ro2, and RF. (d) What is β ? Give an expression for the loop gain Aβ and the amount of feedback (1+Aβ). (e) Derive an expression for Af. (f) Derive expressions for Ri, Rin , Ro, and Rout . (g) Evaluate A, β, Aβ, Af, Ri, Ro, Rin , and Rout for the component values given. Figure P11.65 11.65 The feedback transresistance amplifier in Fig. P11.65 utilizes two identical MOSFETs biased by ideal current sources I = 0.4 mA. The MOSFETs are sized to operate at VOV = 0.2 V and have Vt = 0.5 V and VA = 16 V. The feedback resistance RF = 10 kΩ. (a) If Is has a zero dc component, find the dc voltage at the input, at the drain of Q1, and at the output. (b) Find gm and ro of Q1 and Q2. (c) Provide the A circuit and derive an expression for A in terms of gm1, ro1, gm2, ro2, and RF. (d) What is β ? Give an expression for the loop gain Aβ and the amount of feedback (1+Aβ). (e) Derive an expression for Af. (f) Derive expressions for Ri, Rin , Ro, and Rout . (g) Evaluate A, β, Aβ, Af, Ri, Ro, Rin , and Rout for the component values given. Figure P11.65

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