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university:courses:electronics:electronics-lab-variable-gain-amplifier [26 Mar 2018 11:43]
Antoniu Miclaus add Voltage Controlled Amplifier using transistor
university:courses:electronics:electronics-lab-variable-gain-amplifier [03 Jan 2021 22:21] (current)
Robin Getz fix links
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 Consider the circuit schematic presented in Figure 1. Consider the circuit schematic presented in Figure 1.
  
-<WRAP centeralign>​ {{:​university:​courses:​electronics:​var_gain_amp_crl-sch.png|}} </​WRAP>​+<WRAP centeralign>​ {{ :​university:​courses:​electronics:​vctrl_amp_transistor.png|}} </​WRAP>​
  
 <WRAP centeralign>​ Figure 1. Voltage control using transistor </​WRAP>​ <WRAP centeralign>​ Figure 1. Voltage control using transistor </​WRAP>​
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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 ​peak-to-peak, 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.
  
 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>​ {{ :​university:​courses:​electronics:​var_g_invert_amp_pot.png|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 4. Variable Gain Inverting Amplifier using potetiometer </​WRAP>​
 +
 +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>​ {{:​university:​courses:​electronics:​var_gain_amp_pot2-bb.png|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 5. Variable Gain Inverting Amplifier using potetiometer - breadboard circuit </​WRAP>​
 +
 +==== Procedure ====
 +
 +Use the first waveform generator as source Vin to provide a 2V amplitude peak-to-peak,​ 1 kHz sine wave excitation to the circuit. ​ 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.
 +
 +By varying the value of the potentiometer,​ an animated plot is presented in Figure 6.
 +
 +<WRAP centeralign>​ {{:​university:​courses:​electronics:​var_gain_amp_pot2-wav.gif|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 6. Variable Gain Inverting Amplifier using potetiometer - waveforms </​WRAP>​
 +
 +Using this type of configuration,​ the output is inverted and amplified based on the feedback resistance value.
 +
 +===== Variable Gain Inverting/​Non-Inverting Amplifier using potetiometer =====
 +
 +==== Background ====
 +
 +Consider the circuit schematic presented in Figure 7.
 +
 +<WRAP centeralign>​ {{ :​university:​courses:​electronics:​var_gain_inv_noninv.png|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 7. Variable Gain Inverting/​Non-Inverting Amplifier using potetiometer </​WRAP>​
 +
 +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>​ {{:​university:​courses:​electronics:​var_gain_amp_pot-bb.png|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 8. Variable Gain Inverting/​Non-Inverting Amplifier using potetiometer - breadboard circuit </​WRAP>​
 +
 +==== Procedure ====
 +
 +Use the first waveform generator as source Vin to provide a 2V amplitude peak-to-peak,​ 1 kHz sine wave excitation to the circuit. ​ 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.
 +
 +By varying the value of the potentiometer,​ an animated plot is presented in Figure 9.
 +
 +<WRAP centeralign>​ {{:​university:​courses:​electronics:​var_gain_amp_pot-wav.gif|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 9. Variable Gain Inverting/​Non-Inverting Amplifier using potentiometer - waveforms </​WRAP>​
 +
 +Using this configuration,​ the output is amplified varying between +-Vin.
 +
 +===== 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: [[downgit>​education_tools/​tree/​master/​m2k/​fritzing/​var_gain_amp_bb | var_gain_amp_bb]]
 +  * LTspice files: [[downgit>​education_tools/​tree/​master/​m2k/​ltspice/​var_gain_amp_ltspice | var_gain_amp_ltspice]]
 +</​WRAP>​
 +
 +Some additional resources:
 +  * [[adi>​en/​analog-dialogue/​articles/​x-amp-45-db-500-mhz-variable-gain-amplifier.html|X-Amp™,​ A New 45-dB, 500-MHz Variable-Gain Amplifier (VGA) Simplifies Adaptive Receiver Designs]]
 +  * [[adi>​en/​analog-dialogue/​articles/​reinvent-the-signal-generator.html|Two New Devices Help Reinvent the Signal Generator]]
 +
 +**Return to Lab Activity [[university:​courses:​electronics:​labs|Table of Contents]]**
 +
 +
  
university/courses/electronics/electronics-lab-variable-gain-amplifier.1522057388.txt.gz · Last modified: 26 Mar 2018 11:43 by Antoniu Miclaus