CHAPTER 3: SPECIAL PURPOSE OP-AMP CIRCUITS. Objectives:. Explain and analyze the operation of an instrumentation amplifier. Explain and analyze the operation of an isolation amplifier. Explain and analyze the operation of log and antilog amplifiers. INSTRUMENTATION AMPLIFIER.
A differential voltage-gain device that amplifies the difference between the voltages existing at its two input terminals.
The main purpose is to amplify small signals that may be riding on large common-mode voltages.
It is an integrated circuit that internally has three operational amplifiers and several resistors.
Op-amps A1 and A2 are noninverting configurations that provide high input impedance and voltage gain.
where R1 = R2 = R.
Determine the value of the external gain-setting resistor RG for a certain IC instrumentation amplifier with R1 = R2 = 25 kΩ. The closed-loop voltage gain is to be 500.
Answer : RG = 100 Ω
Calculate the voltage gain and determine the bandwidth using the graph gain vs. frequency for AD622 for the instrumentation amplifier in figure below.
Determine the total voltage gain of the 3656KG isolation amplifier in figure above.
Answer : Av(tot) = 62.7
where IR is a constant for a given diode
Determine the output voltage for the log amplifier in figure above. Assume IR = 50 nA.
Answer : VOUT = -0.150 V
where IEBO is the emitter-to-base leakage current
What is Vout for a transistor log amplifier with Vin = 3 V and R1 = 68 kΩ ? Assume IEBO = 40 nA.
Answer : Vout = -175.1 mV
For the antilog amplifier in figure below, find the output voltage. Assume IEBO = 40 nA.
Answer : Vout = -3V