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university:courses:electronics:electronics-lab-envelope-detector [20 Mar 2018 16:56]
Antoniu Miclaus Biased Envelope Detector: Add Materials + Background
university:courses:electronics:electronics-lab-envelope-detector [10 Mar 2021 17:35] (current)
Cristina Suteu updated math equation to work with Scopy's (v1.2.0) signal generator
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 ===== Objective ===== ===== Objective =====
  
-In this lab activity we will use [[http://​www.analog.com/​en/​design-center/​evaluation-hardware-and-software/​evaluation-boards-kits/​adalm2000.html|ADALM2000]] and [[university:​tools:​m2k:​scopy|Scopy]] to introduce envelope detection and amplitude modulation. The signal'​s envelope is equivalent to its outline, and an envelope detector connects all the peaks in this signal. Envelope detection has numerous applications in the fields of signal processing and communications,​ one of which is amplitude modulation (AM) detection.+In this lab activity we will use [[adi>en/​design-center/​evaluation-hardware-and-software/​evaluation-boards-kits/​adalm2000.html|ADALM2000]] and [[university:​tools:​m2k:​scopy|Scopy]] to introduce envelope detection and amplitude modulation. The signal'​s envelope is equivalent to its outline, and an envelope detector connects all the peaks in this signal. Envelope detection has numerous applications in the fields of signal processing and communications,​ one of which is amplitude modulation (AM) detection.
  
 Amplitude modulation (AM) is a modulation technique used in electronic communication,​ most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being transmitted. That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker,​ or the light intensity of television pixels. ​ Amplitude modulation (AM) is a modulation technique used in electronic communication,​ most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being transmitted. That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker,​ or the light intensity of television pixels. ​
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 Consider the circuit presented in Figure 1. Consider the circuit presented in Figure 1.
  
-<WRAP centeralign>​{{:​university:​courses:​electronics:​env_detector-sch.png?500|}}</​WRAP>​+<WRAP centeralign>​{{ :​university:​courses:​electronics:​env_detector_ltspice.png?400 |}}</​WRAP>​
  
 <WRAP centeralign>​ Figure 1. Basic Envelope Detector Circuit </​WRAP>​ <WRAP centeralign>​ Figure 1. Basic Envelope Detector Circuit </​WRAP>​
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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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   * ω<​sub>​m</​sub>​ = 100Hz   * ω<​sub>​m</​sub>​ = 100Hz
   * 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: //​(1+0.5*cos(t))*3*cos(100*t)//​. The generated waveform is presented in Figure 3.+To generate the AM signal use the math function from the Scopy signal generator. Set the record length ​to 20ms, the sample rate to 75MSPS ​and apply the following function: //​(1+0.5*cos(2*pi*100*t))*3*cos(2*pi*100*100*t)//. The generated waveform is presented in Figure 3.
  
 <WRAP centeralign>​{{:​university:​courses:​electronics:​env_detector-wgen.png|}}</​WRAP>​ <WRAP centeralign>​{{:​university:​courses:​electronics:​env_detector-wgen.png|}}</​WRAP>​
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 Consider the circuit presented in Figure 9. Consider the circuit presented in Figure 9.
  
-<WRAP centeralign>​{{:​university:​courses:​electronics:​ext_env_detector-sch.png?​400|}}</​WRAP>​+<WRAP centeralign>​{{ :​university:​courses:​electronics:​ext_env_det.png?400 |}}</​WRAP>​
  
 <WRAP centeralign>​ Figure 9. Positive and negative Envelope Detector Circuit </​WRAP>​ <WRAP centeralign>​ Figure 9. Positive and negative Envelope Detector Circuit </​WRAP>​
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 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 extended envelope detector circuit. Build the following breadboard circuit for the extended envelope detector circuit.
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 <WRAP centeralign>​ Figure 10. Extended Envelope Detector breadboard circuit </​WRAP>​ <WRAP centeralign>​ Figure 10. Extended Envelope Detector breadboard circuit </​WRAP>​
  
-=== 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<​sub>​m</​sub>​ = 100Hz   * ω<​sub>​m</​sub>​ = 100Hz
   * 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: //​(1+0.5*cos(t))*3*cos(100*t)//​. The generated waveform is presented in Figure 11. (with 5 displayed periods)+To generate the AM signal use the math function from the Scopy signal generator. Set the record length ​to 50ms and apply the following function: //​(1+0.5*cos(2*pi*100*t))*3*cos(2*pi*100*100*t)//. The generated waveform is presented in Figure 11. (with 5 displayed periods)
  
 <WRAP centeralign>​{{:​university:​courses:​electronics:​ext_env_detector-wgen.png|}}</​WRAP>​ <WRAP centeralign>​{{:​university:​courses:​electronics:​ext_env_detector-wgen.png|}}</​WRAP>​
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 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. 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.
  
-==== Materials====+==== Materials ====
  
-ADALM1000 Active Learning Module +ADALM1000 Active Learning Module\\ 
-Solder-less breadboard, and jumper wire kit +Solder-less breadboard, and jumper wire kit\\ 
-1 - 1.5 KΩ resistor (brown green red) +1 - 1.5 KΩ resistor (brown green red)\\ 
-1 - 10 KΩ resistor (brown black orange) +1 - 10 KΩ resistor (brown black orange)\\ 
-1 - 20 KΩ resistor (red black orange) +1 - 20 KΩ resistor (red black orange)\\ 
-2 - 1.0uF capacitor, C1, C2 +2 - 1.0uF capacitor, C1, C2\\ 
-1 - 2N3904 NPN transistor +1 - 2N3904 NPN transistor\\ 
-1 - 1N914 diode+1 - 1N914 diode\\
  
-==== Background====+==== Background ====
  
 Consider the circuit shown in Figure 14. Consider the circuit shown in Figure 14.
  
-<WRAP centeralign>​{{:​university:​courses:​electronics:​bias_env_detector-sch.png|}}</​WRAP>​+<WRAP centeralign>​{{ :​university:​courses:​electronics:​bias_env_detector.png?400 |}}</​WRAP>​
  
 <WRAP centeralign>​ Figure 14. Biased Envelope Detector circuit </​WRAP>​ <WRAP centeralign>​ Figure 14. Biased Envelope Detector circuit </​WRAP>​
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 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:​courses:​electronics:​text:​chapter-7#​diode_clamp|DC restoration]]). Absent any modulated input the DC quiescent operating point seen at the emitter of Q1 will be the voltage at the junction of R1 and R2 minus the diode drop of D1 and the VBE of Q1. The base current of Q1 flows in diode D1 forward biasing it. During the positive half cycles of the modulated input D1 turns off and the input signal peaks charge filter capacitor C2. During the negative half cycles of the input signal transistor Q1 turns off and D1 turns on harder supplying the input current. 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:​courses:​electronics:​text:​chapter-7#​diode_clamp|DC restoration]]). Absent any modulated input the DC quiescent operating point seen at the emitter of Q1 will be the voltage at the junction of R1 and R2 minus the diode drop of D1 and the VBE of Q1. The base current of Q1 flows in diode D1 forward biasing it. During the positive half cycles of the modulated input D1 turns off and the input signal peaks charge filter capacitor C2. During the negative half cycles of the input signal transistor Q1 turns off and D1 turns on harder supplying the input current.
  
-==== Hardware Setup====+==== Hardware Setup ====
  
-===== Further Reading =====+Build the following breadboard circuit for the biased envelope detector circuit.
  
-Additional resources:+<WRAP centeralign>​{{:university:​courses:​electronics:​bias_env_detector-bb.png|}}</​WRAP>​
  
-  * [[http://​www.analog.com/​en/​technical-articles/​integrated-diode-based-rf-detectors.html|Understanding,​ Operating, and Interfacing to Integrated Diode-Based RF Detectors]] +<WRAP centeralign>​ Figure 15Biased ​Envelope Detector ​breadboard circuit </​WRAP>​
-  * [[http://​www.analog.com/​media/​en/​technical-documentation/​application-notes/​AN-423.pdf|Amplitude Modulation of the AD9850 Direct Digital Synthesizer]] +
-  * [[http://​www.analog.com/​en/​analog-dialogue/​raqs/​raq-issue-92.html|Multipliers and Modulators]] +
-  * [[http://​www.analog.com/​media/​en/​technical-documentation/​data-sheets/​ADL5511.pdf|Envelope ​and TruPwr RMS Detector +
-]]+
  
 +==== 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.
 +
 +<WRAP centeralign>​{{:​university:​courses:​electronics:​bias_env_detector-wav.png|}}</​WRAP>​
 +
 +<WRAP centeralign>​ Figure 16. Biased Envelope Detector waveforms </​WRAP>​
 +
 +===== Further Reading =====
 +
 +<WRAP round download>​
 +**Lab Resources:​**
 +  * Fritzing files: [[downgit>​education_tools/​tree/​master/​m2k/​fritzing/​env_detector_bb | env_detector_bb]]
 +  * LTspice files: [[downgit>​education_tools/​tree/​master/​m2k/​ltspice/​env_detector_ltspice | env_detector_ltspice]]
 +</​WRAP>​
 +
 +Additional resources:
 +
 +  * [[adi>​en/​technical-articles/​integrated-diode-based-rf-detectors.html|Understanding,​ Operating, and Interfacing to Integrated Diode-Based RF Detectors]]
 +  * [[adi>​media/​en/​technical-documentation/​application-notes/​AN-423.pdf|Amplitude Modulation of the AD9850 Direct Digital Synthesizer]]
 +  * [[adi>​en/​analog-dialogue/​raqs/​raq-issue-92.html|Multipliers and Modulators]]
 +  * [[adi>​media/​en/​technical-documentation/​data-sheets/​ADL5511.pdf|Envelope and TruPwr RMS Detector
 +]]
  
 **Return to Lab Activity [[university:​courses:​electronics:​labs|Table of Contents]]** **Return to Lab Activity [[university:​courses:​electronics:​labs|Table of Contents]]**
  
  
university/courses/electronics/electronics-lab-envelope-detector.1521561383.txt.gz · Last modified: 20 Mar 2018 16:56 by Antoniu Miclaus