Category Archives: Electronics

A first proof-of-principle of a Tinnitus detector circuit

Posted on 27/07/2011 by | 1 comment

Tinnitus is a condition in which a patient perceives an auditory phantom sound that can take the form of ringing, buzzing, roaring or hissing in the absence of an external sound. Approximately a billion of people suffer from tinnitus worldwide, while in 2% – 3% of the population, tinnitus significantly degrades quality of life of the patients and can lead to insomnia, anxiety and depression.

Currently, there are no proven treatments for tinnitus. However, recent research has shown that tinnitus patients can benefit from electrical brain stimulation. In addition, it has been shown that there is a link between tinnitus perception and a change in the energy levels of several electrocortigography (ECoG) / electroencephalography (EEG) frequency bands. For example, the energies of theta (4-8Hz) and low-gamma (30-50Hz) waves increase, while the energy of alpha (8-12Hz) waves decreases during active tinnitus perception. The same studies suggest that the intensity of the tinnitus perception correlates with the amount of the energy increased in the gamma band.

The real-time tinnitus detection method proposed by the BME group detects tinnitus by comparing ECoG/EEG signal energies from different locations in the brain according to a tinnitus "signature". First, the proposed strategy selects appropriate ECoG/EEG bands per channel by means of band-pass filters. Next, their extracted energies are compared to their counterparts from a different (healthy) location. Tinnitus is detected only if higher theta and gamma energies while lower alpha energy is found when compared to the signals from this healthy region. The applicability of the detector is verified by means of circuit simulations with real neural waveforms and is able to successfully detect tinnitus.

Are you interested in any progress related to the tinnitus detector circuit? Stay tuned.

Senad 

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Posted in Education, Electronics, General, Neurostimulation and Neuromodulation, Understanding the Brain

Small chip to overcome inflammation of joints

Posted on 18/07/2011 by | 1 comment

Today, the Telegraaf and Nu.nl report that a team of the Dutch rheumatologist Paul-Peter Tak of the Amsterdam Academic Medical Center will implant a kind of pacemaker, its size in the order of a bout a square centimeter, that will deliver stimuli to the vagus nerve for about one minute a day. By doing so, it is expected that inflammation of the joints of patients that suffer from rheumatoid arthritis can be reduced or even completely stopped.

Of course, what can be deduced from the article is that this pacemaker, electronics-wise, is nothing more than a simple blinking light with a timer, which can be implemented by means of a miniature microcontroller and a battery. However, it is also obvious that electrical stimulation of the vagus nerve, albeit at its infancy, is already very promising and a possible treatment of a wide range of neural disorders and pain is dawning at the horizon.

Wouter

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Posted in Electronics, General, Neurostimulation and Neuromodulation

New way of data conversion

Posted on 08/07/2011 by | 1 comment

Analog-to-digital converters (ADCs) are indispensable building blocks of wearable and implantable biomedical data acquisition systems. Ultra-low-power ADCs for biomedical signal sensing have witnessed a dramatically reduced power consumption in recent years, but we have to admit that our biomedical systems need more breakthroughs than just squeezing harder in conventional ways.

As is known to all, many biomedical signals are born with a sparse nature. A large amount of redundant digital samples will be thus generated if we use Nyquist-rate ADCs to convert such signals. Most likely, ADC power savings are not a major concern in a system in which transmission power dominates the overall power consumption. However, if this is not the case, from a signal point of view, new ways of sampling or sensing are necessary to further improve the performance of the whole system.

A new and promising ADC approach for biomedical data acquisition is based on so-called level-crossing (LC) sampling, in which samples are generated only when the input signal crosses the threshold levels, so there is no redundant sample in this case. However, the conventional LC-ADC utilizes power hungry comparators and DACs, which causes the LC-ADC to consume much more power than ultra-low-power Nyquist ADCs (e.g., SAR ADCs). In our new approach (mentioned by Wouter earlier in the weblog), innovations at both system level and circuit level enble us to design a more power-efficient LC-ADC. Power consumption is now in the range of hundreds of nanowatts. We are currently investigating the possiblity to further improve its performance and reliability.

Yongjia

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Posted in Electronics, General, Medical Body Area Networks

Smaller can be better

Posted on 07/06/2011 by | Leave a comment

After the 2011 edition of ELCA Music Festival, I was dragged (by some mysterious power) deep into the idea that came to my mind around three years ago. At that time, I was trying to simultaneously linearize and reduce a transconductance of a Gm cell (V–I converter circuit) for very low frequency biomedical filtering. The linearization and transconductance reduction were successful but the success came prices that I needed to pay:

  1. circuit complexity which is really unfriendly to weak inversion CMOS.
  2. more current consumption which was not surprising. It was very well in line with the circuit complexity. 
  3. more noise contribution (this was also a good friend with circuit complexity).

When I looked into the dynamic range of my design, it was not improved that much from that of an ordinary differential pair circuit (even so the paper was published [1] :). Then I got an idea that ‘instead of inventing a sophisticated linearization technique to obtain larger dynamic range, trying to use as less as possible noisy circuit elements and forget about linearization are more reasonable for biomedical signal processing which requires a good deal of power reduction’. The idea was left there since then for two reasons: I had other jobs to do and the idea seemed too sloppy.

Let me tell you more about the mysterious power. Several times we did rehearsals before the ELCA festival. I was in charge of acoustic guitar and harmonica for the song called ‘The end of the world’ http://www.youtube.com/watch?v=KmnKCE99sYE. Playing two instruments at the same time made me tired and it did not make a good harmony as expected. So I stopped playing the guitar and exercised only the harmonica (of course combined with the piano from Wouter, the electric guitar of Mark and Wannaya’s voice (I could not find this song on our Youtube channel — don’t know why). The song turned out better than before and this reminded me of that sloppy idea!!!

I did an investigation and found that there are strong evidences supporting my idea founded in low-pass filter design [2] [3]… It works!!! Large dynamic range was achieved as well as a very good figure of merit. Although the above filters were dedicated to communication systems rather than for low frequency biomedical signals, the underlying concept of the filter should be applicable for biomedical signal as well. Only a bit more effort was needed to work it out.

Good news!!! Recently, with the help from Senad, who has become 22 years old today — the same as me :). Happy Birthday!!!— my sloppy idea was realized. A 6th-order ECG low-pass filter with a large dynamic range of 59dB and extremely low power consumption of 0.45nW has been designed. We plan to submit this work to BioCAS2011. Hopefully, the reviewers will like it, too.

More good news!!! The application is not limited to low-pass filters only. I’m developing this idea further to apply it for a cochlear channel band-pass filter. What I can say now from the circuit simulations is that the filter provides the best figure of merit compared to state of the art designs. The secret is that all terminals of a single MOSFET device are being used, one pole and one zero are achieved by only two transistors sharing the same bias current.

Next time, I will tell you more about this. Stay tuned if you are interested!!!

Healthy Haring is coming. I heard from Marijn that this year, since the weather is warm, the fish is growing bigger. See you in the Pub this coming Thursday for Harings and Beers 😀

June

[1] C. Sawigun, D. Pal and A. Demosthenous, “A wide linear range transconductor subthreshold transconductor for sub-Hz filtering,” Proc. IEEE ISCAS, pp.1567-1570, 2010

[2] D. Python, A. S. Porret and C. Enz, “A 1V 5th-order Bessel filter dedicated to digital standard proceses,” Proc. IEEE CICC, pp. 505-508, 1999

[3] S. D’Amico, M. Conta and A. Baschirotto, “A 4.1mW 10MHz fourth-order source-follower-based continuous-time filter with 79-dB DR,” IEEE J. Solid-State Circuits, pp. 2713-2719, Dec. 2006

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Posted in Electronics, General, Pacemakers

Unexpected Meet and Greet with Hero in Circuit Theory

Posted on 08/05/2011 by | Leave a comment

Georg Simon OhmLast week, I was in Köln, Koeln, Keulen or Cologne (depending on from which country you are) with my family and while on our way to the Dom, Cologne’s well-known cathedral, I bumped into one of the greatest heroes of electric circuit theory: Georg Simon Ohm. The sign says that "George Simon Ohm discovered, in this house, being a teacher at the Old Gymnasium in Cologne, in 1826, the foundation of electric current."

Though one of the most important discoveries indeed, I think it is not so much the discovery of the foundation of electric current, but rather the relation between voltage and current that holds for linear resistances (and impedances, in the harmonic regime), later known as "Ohm’s Law" that caused his name to be remembered forever.

For those that have both an interest in technology and law, I cordially recommend Ohm’s Law and Kirchhoff’s Laws as basic study material.

Wouter

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Posted in Education, Electronics, General

Can the upcoming solar storm turn your pacemaker into a killer inside you?

Posted on 17/02/2011 by | 4 comments

It has been predicted that today (Febr. 17, 2011) one of the largest solar storms in years will reach the earth and may interfere with sensitive electronic equipment, such as GPS receivers in cars and PDAs. Also air traffic and power grids may suffer from this kind of interference.

 Solar Storm 

Solar storms, also called geomagnetic storms, are caused by solar coronal mass ejections and modify the electromagnetic fields in the ionosphere, magnetosphere and heliosphere. They usually last only one or two days and can cause auroras further away from the poles than usually. According to Wikipedia, "On March 13, 1989 a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds as equipment protection relays tripped in a cascading sequence of events. Six million people were left without power for nine hours, with significant economic loss."

So how dangerous are these solar storms for life-supporting devices like pacemakers and neurostimulators? In order to answer this question, we need to understand the physical and electrical effects of solar storms. Solar storms induce fluctuations in the Earth’s magnetic field. These fluctuations, in turn, can induce currents in large electrically conducting structures, such as power grids and metal pipelines, leading to damaged transformers and corrosion. Solar storms also influence the electrical currents in the magnetosphere and the ionosphere and thereby affect wireless communication that propagates through them.

So my conclusion: as long as you do not use your shortwave radio or CB set to control your implantable device remotely and you do not power it from the mains, you’re safe. Ain’t that a relief?

Wouter

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Posted in Electronics, General, Neurostimulation and Neuromodulation, Pacemakers