Envelope Detector Software
I am working on a project in which we are trying to design and build an ultrasonic thickness gauge that will calculate the thickness of a given part based on the time difference between sending a signal and receiving a reflection back (using the known speed of sound through the medium). As we are in the initial stages of prototyping, we are currently using an Arduino nano as the MCU for our prototype. We have successfully amplified the pulse generated by the MCU to a higher voltage, which is then used to excite the ultrasonic transducer (which is in contact with the part that is being measured). The reflection is then detected by the second element of the transducer and converted into an electric signal that is centred around the natural frequency of the transducer (5MHz).
Envelope Detection Algorithm for an Amplitude. The best known means of obtaining such information is a software package. To detect the envelope. If you want to try making a peak detector circuit (envelope detector). (envelope detector). Forum software by XenForo™ ©2010-2017 XenForo Ltd. Recently I've been thinking about the process of envelope detection. Law Envelope Detection. Another digital envelope detector. Software development.
This signal is then processed (amplified and filtered) into a level that would be detectable by the MCU (circuit and scope screenshot as shown below). However due to MCU's limited sampling rate, the signal will not be reliably detected. Therefore I was wondering if we would be able to devise an envelope detector that would extract the amplitude modulation of the reflection signal, effectively converting a very high frequency into a lower frequency signal, which I am hoping would be detected by the MCU. According to what I have read so far, this would be achieved by first rectifying the signal using a “super-diode” (precision rectifier configuration as shown below) and then integrate it through an op-amp integrator. However, it seems that because I am relying on single supply and the frequency of the signal of interest is very high, the rectifier will not work as I expected, in fact I did not get anything out of it. Is there perhaps a way of designing an envelope detector entirely from transistors instead of op-amps? Any pointers or suggestions will be highly appreciated!!
Thanks in advance! Even with a very fast op amp such as the LM7171, the classic op amp-based 'precision rectifier' circuit such as the one you showed is going to be completely helpless in the face of a 5 MHz input signal. As you found, it simply does not work. If you want to try making a peak detector circuit (envelope detector) from transistors that will handle the high frequencies you're dealing with, try the following: The above was adapted from a 'High Speed Adaptive Trigger Circuit' design in Linear Technology, Inc.' See Figure 63 on page 29.
The input to the circuit should be driven from a fast buffer amplifier with low output impedance. The envelope output is high impedance and should be buffered before attempting to drive an ADC. The circuit is not high precision (I assumed your application doesn't require it); the output will be offset from the input by as much as several hundred millivolts. But it should be fast. In which parameters of the received signal are you interested?
Is it the specific waveform or simply the time delay between transmitted pulse and received pulse? In the latter case, I think you can simplify the circuit considerably:. no need for an active high pass filter. The coupling capacitors will suffice to suppress low frequency noise and DC. Use the second stage for more gain instead. no need for an active rectifier circuit. With enough signal amplitude a simple diode rectifier should suffice.
Or the circuit recommended by OBW0549 which is also moderately complex. no need for an integrator.
A simple RC low passs filter should suffice. Essentially what was used in a century ago. Even with a very fast op amp such as the LM7171, the classic op amp-based 'precision rectifier' circuit such as the one you showed is going to be completely helpless in the face of a 5 MHz input signal. As you found, it simply does not work. If you want to try making a peak detector circuit (envelope detector) from transistors that will handle the high frequencies you're dealing with, try the following: The above was adapted from a 'High Speed Adaptive Trigger Circuit' design in Linear Technology, Inc.' See Figure 63 on page 29. The input to the circuit should be driven from a fast buffer amplifier with low output impedance.
The envelope output is high impedance and should be buffered before attempting to drive an ADC. The circuit is not high precision (I assumed your application doesn't require it); the output will be offset from the input by as much as several hundred millivolts. But it should be fast. In which parameters of the received signal are you interested?
Is it the specific waveform or simply the time delay between transmitted pulse and received pulse? In the latter case, I think you can simplify the circuit considerably:. no need for an active high pass filter. The coupling capacitors will suffice to suppress low frequency noise and DC.
Use the second stage for more gain instead. no need for an active rectifier circuit. With enough signal amplitude a simple diode rectifier should suffice. Or the circuit recommended by OBW0549 which is also moderately complex.
no need for an integrator. A simple RC low passs filter should suffice. Essentially what was used in a century ago. From the very start of this thread I've had my reservations regarding employing sonar (slow as a snail) techniques to measure differences in inches. I would totally expect the transmitted burst to collide with the reflected echo before the transmitted burst completed the burst width.
Perhaps I'm missing something. You also said something in your first post that raised my eyebrows. That would be this statement.
5 MHz is far above the 'sonic' spectrum. What ultrasonic transducer do you have that specs that?
Hi Aldo, Thanks for using the TI E2E Forums! This is from a previous discussion on this very subject: Envelope detection can be accomplished with an op amp based precision rectifier, but often the simple diode detectors are sufficient for general applications.
Rf Envelope Detector
If precision detection is required, then take a look at the TI Precision Design (TIPD) for a precision rectifier: This will provide you some idea as to what is required to attain precision performance. The ac performance of the operational amplifier must be correct for the application. You will note that the op amps in the TIPD are higher current, wide bandwidth amplifiers. The low power requirement must be kept in perspective in relation to the ac performance requirements. National Semi had various precision rectifier circuits in some of their operational amplifier data sheets. A Google search will show some alternative circuits for the and the LM301. In reply to: Hello Aldo, Take a look at Fig 2 in the attached.pdf which shows a L/R audio envelope circuit that's used as part of an audio envelope tracking power supply design.
If your design uses only one channel, then you could eliminate one of the input OA circuits and make the output stage a non-inverting unity gain stage. The is a quad OA so the whole circuit would require only one device plus diodes and passives. You might want to do some gain scaling of the input stage and use +/- supplies if available. The input is AC coupled. All content and materials on this site are provided 'as is'. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials.
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