![]() ![]() 4 Responses to “25: Operational Amplifiers” A non-inverting summing amplifier is used in a circuit with Va=1Vdc, Vb=3Vdc, Vc=5Vdc, Ra=Rb=Rc, RF=28k ohms, and RB=14k ohms. If the input to the first op amp is 0.1Vpp what is the output of the third op amp and what is its phase relationship with the input?ħ. The second and third op amps are setup in an inverting configuration, both with RF=50k and R1=20k. The first op amp is a non-inverting amplifier with RF=100k and R1=25k. Three amplifiers are used in a cascaded arrangement, that is, the output of the first amplifier is the input to the next and the output of the second amplifier is the input to the third. ![]() What is the value of the unknown resistor (RF)?Ħ. Since the input and output are in phase you assume that the amplifier is a non-inverting amplifier. You also measure the input and output waveforms and they are 0.25Vpp and 2Vpp respectively. You find that one resistor is 48k ohms (R1). You know it is an amplifier, but you cannot make out the color bands on one of the resistors. You are given a circuit and asked to replace the components because the functionality at high frequency has dimished over the past few months, but it still works at DC. The output voltage has no DC offset, it is just a 1.6Vpp wave. ![]() A differential amplifier is used in a situation where the input voltage (Va) is 0.8Vpp with a. If R1=24k ohms and RF=8k ohms what is the output voltage amplitude if the input voltage amplitude is 1.5Vpp when an inverting amplifier is used?Ĥ. If R1=RF, what is the gain of a non-inverting amplifier?ģ. True or False, given the same RF and R1 values, the gain of a non-inverting amplifier is always larger than the absolute value of the gain of the inverting amplifier.Ģ. You should now be prepared to answer the following questions:ġ. Stienecker)įor example: If Vin = 2.2Vpp 1.2kHz the output of a voltage follower would be, Vout = 2.2V 1.2kHz in phase.įor example: If Vin = 1Vpp and RF=60k ohms and R1=30k ohms then the gain is 3 V/V so therefore, the output, Vout = Vin x Gain = 3Vpp in phase.įor example: If Vin = 0.8Vpp 700kHz and RF=60k ohms and R1=30k ohms then the gain is -2V/V so therefore, the output, Vout = Vin x Gain = 1.6Vpp out of phase.įor example: If Vin(Va) = 2Vpp with a 1Vdc offset 300kHz, Ra=R1=10k ohms, RF=Rx=15k ohms, and Va=1Vdc then then the output, Vout = (Vin – Va) x Gain = 3Vpp.įor example: if Va=1Vdc, Vb=2Vdc, Vc=3Vdc, Ra=Rb=Rc=100k ohms, RF=24k ohms, RB=12k ohms then Vout = (1+2)((1+2+3)/3)=3*(6/3)=6Vdc. TOPIC 3: Operational Amplifier Applications (Listen to Dr. ![]() TOPIC 2: Operational Amplifiers Feedback and Gain (Listen to Dr. A soldered circuit with all component lead lengths minimised might be needed.TOPIC 1: Operational Amplifier Basics (Listen to Dr. In some cases, the circuit will never work if built onto prototype board. Some experimentation might be needed to get the right value. The feedback capacitor restricts high frequency performance. This circuit shows some techniques to minimise the risk of oscillation. Lack of decoupling, poor layout and stray capacitance and resistance on prototype boards are all possible causes. Parasitic oscillations are caused by unwanted positive feedback, usually at higher frequencies.
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