Problem 1

The circuit in Fig 1 uses a potentiometer whose total resistance is R1. The movable stylus on terminal 2 creates two variable resistors: (1-β) R1 between terminals 1-2 and β R1 between terminals 2-3. The movable stylus varies β over the range 0 ≤ β ≤ 1.

Fig. 1. Circuit to be evaluated [2].

Analysis

1. Derive an expressior for gain G = v_o/v_s in terms of β. Show all steps and annotate as necessary.

2. Calculate the amplifier gain for β = 0.0, β = 0.5, and β =1.0 with component values R1=10kΩ and R2=1.5kΩ.

Problem 2

An Op-Amp circuit is shown below. For the ideal Op-Amp with A = ∞

a) find V_o and

b) the input impedance R_i = V_i/I_i.

c) Next assume A = 6 V/V, and repeat part a) and find V_o

Problem 3

A current amplifier is characterized by a short-circuit current gain A_i = 50, an input resistance Ri of 500, and an output resistance R_o of 2K.

Assume that the input of the current amplifier is driven by a voltage source with an open-circuit voltage Vs and a series resistance of R_s.= 250. Assume also that the output is loaded with a resistance R_L of 2K. Let the output voltage be designated by V_o.

Determine the voltage gain V_o/V_s in dB.