Logarithmic amplifier
Carry out all analyses before coming to the lab
Use Vcc=9V; Ignore the additional bias resistor of 3R initially
Assuming an ideal opamp, and an ideal exponential transistor, determine the output Vout and the transistor current Ic in the circuit in (a-i). What is the range of Vin over which the circuit functions correctly?
Modeling the transistor with a transconductance gm, 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 Vin?
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 Vcc=9V; Ignore the additional bias resistor of 3R initially
Assuming an ideal opamp, and an ideal exponential transistor, determine the output Vout and the transistor current Ic in the circuit in (b-i). What is the range of Vin over which the circuit functions correctly?
Modeling the transistor with a transconductance gm, 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 Vin? 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 Vcc=9V; Ignore the additional bias resistor of 3R initially
Assuming an ideal opamp, and an ideal exponential transistor, determine the output Vout and the transistor current Ic in the circuit in (c-i). What is the range of Vin over which the circuit functions correctly?
Modeling the transistor with a transconductance gm, 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 Vin?
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?