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university:courses:electronics:electronics-lab-variable-gain-amplifier [26 Mar 2018 11:43] – add Voltage Controlled Amplifier using transistor Antoniu Miclaus | university:courses:electronics:electronics-lab-variable-gain-amplifier [23 Aug 2019 15:14] – Antoniu Miclaus | ||
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Consider the circuit schematic presented in Figure 1. | Consider the circuit schematic presented in Figure 1. | ||
- | <WRAP centeralign> | + | <WRAP centeralign> |
<WRAP centeralign> | <WRAP centeralign> | ||
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==== Procedure ==== | ==== Procedure ==== | ||
- | Use the first waveform generator as source Vin to provide a 2V amplitude, 1 kHz sine wave excitation to the circuit. Use the second waveform generator for controlling the transistor, providing a 2V amplitude, 1Hz square wave excitation. Supply the op amp to +/- 5V from the power supply. Configure the scope so that the input signal is displayed on channel 1 and the output signal is displayed on channel 2. | + | Use the first waveform generator as source Vin to provide a 2V amplitude |
An animated plot is presented in Figure 3. | An animated plot is presented in Figure 3. | ||
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The output signal varies between two values, determined by the two gain settings, based on the state of the controlled transistor. | 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: | ||
+ | |||
+ | |||