Logarithmic amplifier

Carry out all analyses before coming to the lab

• Use V_cc=9V; Ignore the additional bias resistor of 3R initially
• Assuming an ideal opamp, and an ideal exponential transistor, determine the output V_out and the transistor current I_c in the circuit in (a-i). What is the range of V_in over which the circuit functions correctly?
• Modeling the transistor with a transconductance g_m, determine the small signal loop gain of the circuit. You can break the loop at the inverting input of the opamp as shown in (a-ii), and assume that the opamp's gain is A(s).
• Does the loop gain depend on the input voltage V_in?
• Build the circuit and verify the functionality determined above. Apply a 1kHz square wave input varying between -0.25V and -2.5V and observe the output.
• Connect the additional bias resistor and observer the output with bipolar inputs? What is the largest allowable input amplitude?

• Use V_cc=9V; Ignore the additional bias resistor of 3R initially
• Assuming an ideal opamp, and an ideal exponential transistor, determine the output V_out and the transistor current I_c in the circuit in (b-i). What is the range of V_in over which the circuit functions correctly?
• Modeling the transistor with a transconductance g_m, determine the small signal loop gain of the circuit. You can break the loop at the inverting input of the opamp as shown in (b-ii), and assume that the opamp's gain is A(s).
• Does the loop gain depend on the input voltage V_in? What does it mean for the stability of the circuit?
• Build the circuit and verify the functionality determined above. Apply a 1kHz square wave input varying between +0.25V and +2.5V and observe the output.
• Connect the additional bias resistor and observer the output with bipolar inputs? What is the largest allowable input amplitude?

• Use V_cc=9V; Ignore the additional bias resistor of 3R initially
• Assuming an ideal opamp, and an ideal exponential transistor, determine the output V_out and the transistor current I_c in the circuit in (c-i). What is the range of V_in over which the circuit functions correctly?
• Modeling the transistor with a transconductance g_m, determine the small signal loop gain of the circuit. You can break the loop at the inverting input of the opamp as shown in (c-ii), and assume that the opamp's gain is A(s).
• Does the loop gain depend on the input voltage V_in?
• Build the circuit and verify the functionality determined above. Apply a 1kHz square wave input varying between +0.25V and +2.5V and observe the output.
• Connect the additional bias resistor and observer the output with bipolar inputs? What is the largest allowable input amplitude?