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university:courses:electronics:electronics-lab-envelope-detector [28 Feb 2018 13:56] – add questions and further reading Antoniu Miclaus | university:courses:electronics:electronics-lab-envelope-detector [03 Jan 2021 22:21] – fix links Robin Getz | ||
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===== Objective ===== | ===== Objective ===== | ||
- | In this lab activity we will use [[http:// | + | In this lab activity we will use [[adi>en/ |
Amplitude modulation (AM) is a modulation technique used in electronic communication, | Amplitude modulation (AM) is a modulation technique used in electronic communication, | ||
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Consider the circuit presented in Figure 1. | Consider the circuit presented in Figure 1. | ||
- | <WRAP centeralign> | + | <WRAP centeralign> |
<WRAP centeralign> | <WRAP centeralign> | ||
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The capacitor in the circuit stores up charge on the rising edge, and releases it slowly through the resistor when the signal falls. The diode in series rectifies the incoming signal, allowing current flow only when the positive input terminal is at a higher potential than the negative input terminal. | The capacitor in the circuit stores up charge on the rising edge, and releases it slowly through the resistor when the signal falls. The diode in series rectifies the incoming signal, allowing current flow only when the positive input terminal is at a higher potential than the negative input terminal. | ||
- | ==== Hardware Setup: ==== | + | ==== Hardware Setup ==== |
Build the following breadboard circuit for the envelope detector circuit. | Build the following breadboard circuit for the envelope detector circuit. | ||
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<WRAP centeralign> | <WRAP centeralign> | ||
- | === Procedure: === | + | ==== Procedure |
Use the first waveform generator as source to provide the AM signal, with the following parameters: | Use the first waveform generator as source to provide the AM signal, with the following parameters: | ||
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<WRAP centeralign> | <WRAP centeralign> | ||
- | The obtained signal is the envelope of the positive half wave obtained previously. It is actually the 100 Hz message signal with some 10 KHz variations on it. | + | The obtained signal is the envelope of the positive half wave obtained previously. It is actually the 100 Hz message signal with some 10 KHz variations on it (introduced by the carrier signal). |
+ | |||
+ | ==== Frequency Domain Spectrum ==== | ||
+ | |||
+ | We can also view these signals in the frequency domain using the Spectrum Analyzer tool. First we can look at the 10 KHz carrier and 100 Hz message signals together (since both are present at the output of this circuit). Enable channel 1 and set the sweep range from 10 Hz to 15kHz. Run a single sweep. Enable markers 1 and 2 from the Markers tab and the Marker Table. Move each marker using "Prev Peak", "Next Peak" to set them on the carrier and the message signal. A plot example is presented in Figure 6. | ||
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+ | <WRAP centeralign> | ||
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+ | <WRAP centeralign> | ||
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+ | Set the Sweep range from 9 kHz to 11kHz. In Figure 7, the main peak is at the 10 KHz carrier frequency and there are the modulation side-bands +/- 100 Hz on either side of the carrier. (i.e. 9900 Hz and 10100 Hz). | ||
+ | |||
+ | <WRAP centeralign> | ||
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+ | <WRAP centeralign> | ||
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+ | Set the Sweep range from 20Hz to 180Hz. In Figure 8, the main peak is at the 100Hz message frequency. | ||
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+ | <WRAP centeralign> | ||
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+ | <WRAP centeralign> | ||
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+ | Since the frequency analysis is made on the output signal using a basic envelope detector circuit, we are able to see both the message and carrier signal. In contrast to the applied input signal, where the carrier amplitude is larger than the message amplitude, on the spectrum analyzer plot we can notice that, in terms of magnitude, the message signal (100 Hz) is emphasized with respect to the carrier signal (see Marker table). | ||
===== Extended Envelope Detector ===== | ===== Extended Envelope Detector ===== | ||
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==== Background ==== | ==== Background ==== | ||
- | Consider the circuit presented in Figure | + | Consider the circuit presented in Figure |
- | <WRAP centeralign> | + | <WRAP centeralign> |
- | <WRAP centeralign> | + | <WRAP centeralign> |
A similar circuit is added to the circuit in Figure 1 , the only difference being that the diode is reversed, allowing the negative voltages to pass through the RC circuit. | A similar circuit is added to the circuit in Figure 1 , the only difference being that the diode is reversed, allowing the negative voltages to pass through the RC circuit. | ||
- | ==== Hardware Setup: ==== | + | ==== Hardware Setup ==== |
- | Build the following breadboard circuit for the envelope detector circuit. | + | Build the following breadboard circuit for the extended |
<WRAP centeralign> | <WRAP centeralign> | ||
- | <WRAP centeralign> | + | <WRAP centeralign> |
- | === Procedure: === | + | === Procedure === |
Use the first waveform generator as source to provide the AM signal, with the following parameters: | Use the first waveform generator as source to provide the AM signal, with the following parameters: | ||
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* ω< | * ω< | ||
* A = 3 | * A = 3 | ||
- | To generate the AM signal use the math function from the Scopy signal generator. Set the main frequency to 100Hz and apply the following function: // | + | To generate the AM signal use the math function from the Scopy signal generator. Set the main frequency to 100Hz and apply the following function: // |
<WRAP centeralign> | <WRAP centeralign> | ||
- | <WRAP centeralign> | + | <WRAP centeralign> |
Configure the scope so that output signal is displayed on channel 1. | Configure the scope so that output signal is displayed on channel 1. | ||
- | Disconnect the capacitors C1 and C2 from the circuit and observe the output signal. A plot example is presented in Figure | + | Disconnect the capacitors C1 and C2 from the circuit and observe the output signal. A plot example is presented in Figure |
<WRAP centeralign> | <WRAP centeralign> | ||
- | <WRAP centeralign> | + | <WRAP centeralign> |
Without the capacitors connected, the circuit works like a positive half-wave rectifier and negative half-wave rectifier, separating the positive half from the negative one. | Without the capacitors connected, the circuit works like a positive half-wave rectifier and negative half-wave rectifier, separating the positive half from the negative one. | ||
- | Now connect the capacitor back to the circuit. A plot example is presented in Figure | + | Now connect the capacitor back to the circuit. A plot example is presented in Figure |
<WRAP centeralign> | <WRAP centeralign> | ||
- | <WRAP centeralign> | + | <WRAP centeralign> |
The obtained signal is the envelope of the positive half wave and negative half wave obtained previously. | The obtained signal is the envelope of the positive half wave and negative half wave obtained previously. | ||
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1. What happens if the capacitor/ | 1. What happens if the capacitor/ | ||
- | 2. For the circuit in Figure 1, if a resistor is added in series with the diode, between D1 and R1, how will this affect | + | 2. For the circuit in Figure 1, if a resistor is added in series with the diode, between D1 and R1, how is the output |
- | ===== Further Reading | + | ===== Extra Activity: Biased Envelope Detector |
- | Additional resources: | + | The simple diode based envelope detector of Figure 1 does not well or at all if the amplitude i.e. Swing is less than the forward turn voltage of the diode. It will suffer significant distortion on the negative half of the modulation signal for high modulation indexes (near 100%) when the diode is not fully turned on. A way around this limitation is to introduce a small DC bias to the diode. This small bias current moves to quiescent operating point of the circuit to right at the turn on point of the diode. |
- | * [[http:// | + | ==== Materials ==== |
- | * [[http:// | + | |
- | * [[http:// | + | |
- | * [[http:// | + | |
- | ]] | + | |
+ | ADALM1000 Active Learning Module\\ | ||
+ | Solder-less breadboard, and jumper wire kit\\ | ||
+ | 1 - 1.5 KΩ resistor (brown green red)\\ | ||
+ | 1 - 10 KΩ resistor (brown black orange)\\ | ||
+ | 1 - 20 KΩ resistor (red black orange)\\ | ||
+ | 2 - 1.0uF capacitor, C1, C2\\ | ||
+ | 1 - 2N3904 NPN transistor\\ | ||
+ | 1 - 1N914 diode\\ | ||
+ | ==== Background ==== | ||
+ | Consider the circuit shown in Figure 14. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | The amplitude modulated signal is AC coupled into the Base of NPN transistor Q1 which is configured as an emitter follower. Voltage divider R1 and R2 along with diode D1 act to set the DC bias point of the AC coupled input ([[university: | ||
+ | |||
+ | ==== Hardware Setup ==== | ||
+ | |||
+ | Build the following breadboard circuit for the biased envelope detector circuit. | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | |||
+ | ==== Procedure ==== | ||
+ | |||
+ | Connect the circuit to 5V supply. | ||
+ | |||
+ | To test this circuit first use the same modulated signal you used in the simple diode envelope detector example. Compare the new design to the simple diode envelope detector. Using the same steps as earlier generate AM signals with smaller amplitudes / higher modulation indexes and compare the outputs of these two detector designs. | ||
+ | |||
+ | A plot example of the input and output waveforms for the biased envelope detector is presented in Figure 16. | ||
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+ | <WRAP centeralign> | ||
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+ | <WRAP centeralign> | ||
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+ | ===== Further Reading ===== | ||
+ | |||
+ | <WRAP round download> | ||
+ | **Lab Resources: | ||
+ | * Fritzing files: [[downgit> | ||
+ | * LTspice files: [[downgit> | ||
+ | </ | ||
+ | |||
+ | Additional resources: | ||
+ | |||
+ | * [[adi> | ||
+ | * [[adi> | ||
+ | * [[adi> | ||
+ | * [[adi> | ||
+ | ]] | ||
**Return to Lab Activity [[university: | **Return to Lab Activity [[university: | ||