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university:courses:electronics:electronics-lab-variable-gain-amplifier [26 Mar 2018 10:46]
amiclaus add materials
university:courses:electronics:electronics-lab-variable-gain-amplifier [23 Aug 2019 15:14] (current)
amiclaus
Line 19: Line 19:
 1 OP97 operational amplifier\\ 1 OP97 operational amplifier\\
 1 2N3904 npn transistor\\ 1 2N3904 npn transistor\\
 +
 +===== Voltage Controlled Amplifier using transistor =====
 +
 +==== Background ====
 +
 +Consider the circuit schematic presented in Figure 1.
 +
 +<WRAP centeralign>​ {{ :​university:​courses:​electronics:​vctrl_amp_transistor.png|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 1. Voltage control using transistor </​WRAP>​
 +
 +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>​ {{:​university:​courses:​electronics:​var_gain_amp_crl-bb.png|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 2. Voltage control using transistor 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. 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.
 +
 +<WRAP centeralign>​ {{:​university:​courses:​electronics:​var_gain_amp_crl-wav.gif|}} </​WRAP>​
 +
 +<WRAP centeralign>​ Figure 2. Voltage control using transistor waveforms </​WRAP>​
 +
 +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: [[ https://​minhaskamal.github.io/​DownGit/#/​home?​url=https://​github.com/​analogdevicesinc/​education_tools/​tree/​master/​m2k/​fritzing/​var_gain_amp_bb | var_gain_amp_bb]]
 +  * LTspice files: [[ https://​minhaskamal.github.io/​DownGit/#/​home?​url=https://​github.com/​analogdevicesinc/​education_tools/​tree/​master/​m2k/​ltspice/​var_gain_amp_ltspice | var_gain_amp_ltspice]]
 +</​WRAP>​
 +
 +Some additional resources:
 +  * [[http://​www.analog.com/​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]]
 +  * [[http://​www.analog.com/​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.1522054002.txt.gz · Last modified: 26 Mar 2018 10:46 by amiclaus