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university:courses:electronics:electronics-lab-variable-gain-amplifier [26 Mar 2018 10:39] – created Antoniu Miclaus | university:courses:electronics:electronics-lab-variable-gain-amplifier [23 Aug 2019 15:14] – Antoniu Miclaus | ||
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====== Activity: Variable Gain Amplifiers ====== | ====== Activity: Variable Gain Amplifiers ====== | ||
- | ===== Objective: ===== | + | ===== Objective ===== |
In this laboratory we continue our discussion on operational amplifiers (see the previous lab here: [[university: | In this laboratory we continue our discussion on operational amplifiers (see the previous lab here: [[university: | ||
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A variable-gain or voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage. This type of circuit has many applications, | A variable-gain or voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage. This type of circuit has many applications, | ||
+ | |||
+ | ===== Materials ===== | ||
+ | |||
+ | ADALM2000 Active Learning Module\\ | ||
+ | Solder-less breadboard, and jumper wire kit\\ | ||
+ | 2 1 kΩ resistor\\ | ||
+ | 1 4.7 kΩ resistors\\ | ||
+ | 3 10 kΩ resistors\\ | ||
+ | 1 10 kΩ potentiometer\\ | ||
+ | 1 OP97 operational amplifier\\ | ||
+ | 1 2N3904 npn transistor\\ | ||
+ | |||
+ | ===== Voltage Controlled Amplifier using transistor ===== | ||
+ | |||
+ | ==== Background ==== | ||
+ | |||
+ | Consider the circuit schematic presented in Figure 1. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | The configuration of the circuit is similar to a basic non-inverting amplifier. The only addition consists of a transistor and a resistor in parallel with resistor R2. The transistor works as a switch that allows 2 gain settings, based on its current state (on/off). | ||
+ | |||
+ | ==== Hardware Setup ==== | ||
+ | |||
+ | Build the following breadboard circuit for the voltage-controlled amplifier using transistors. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | ==== Procedure ==== | ||
+ | |||
+ | Use the first waveform generator as source Vin to provide a 2V amplitude peak-to-peak, | ||
+ | |||
+ | An animated plot is presented in Figure 3. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | The output signal varies between two values, determined by the two gain settings, based on the state of the controlled transistor. | ||
+ | |||
+ | ===== Variable Gain Inverting Amplifier using potetiometer ===== | ||
+ | |||
+ | ==== Background ==== | ||
+ | |||
+ | Consider the circuit schematic presented in Figure 4. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | On the inverting amplifier a potentiometer is used to control manually the output voltage, replacing the standard feedback resistor. | ||
+ | |||
+ | ==== Hardware Setup ==== | ||
+ | |||
+ | Build the following breadboard circuit for the voltage-controlled amplifier using transistors. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | ==== Procedure ==== | ||
+ | |||
+ | Use the first waveform generator as source Vin to provide a 2V amplitude peak-to-peak, | ||
+ | |||
+ | By varying the value of the potentiometer, | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | Using this type of configuration, | ||
+ | |||
+ | ===== Variable Gain Inverting/ | ||
+ | |||
+ | ==== Background ==== | ||
+ | |||
+ | Consider the circuit schematic presented in Figure 7. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | In this amplifier configuration a potentiometer is used to control manually the output voltage, being able to invert the input by adjusting properly the potentiometer. | ||
+ | |||
+ | ==== Hardware Setup ==== | ||
+ | |||
+ | Build the following breadboard circuit for the voltage-controlled amplifier using transistors. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | ==== Procedure ==== | ||
+ | |||
+ | Use the first waveform generator as source Vin to provide a 2V amplitude peak-to-peak, | ||
+ | |||
+ | By varying the value of the potentiometer, | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | Using this configuration, | ||
+ | |||
+ | ===== Questions ===== | ||
+ | |||
+ | 1. Which are the gain values for each of the circuits used in this lab activity? | ||
+ | |||
+ | 2. Based on the input signals and the computed gains, which are the expected output values? Compute and compare them with the measured values. | ||
+ | |||
+ | 3. Considering the circuit in Figure 7, how can you increase the output range above +-Vin? | ||
+ | |||
+ | ===== Further Reading ===== | ||
+ | |||
+ | <WRAP round download> | ||
+ | **Lab Resources: | ||
+ | * Fritzing files: [[ https:// | ||
+ | * LTspice files: [[ https:// | ||
+ | </ | ||
+ | |||
+ | Some additional resources: | ||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | |||
+ | **Return to Lab Activity [[university: | ||
+ | |||
+ | |||
+ |