Category Archives: cochlear implants

Cochlear implant development going at a rapid pace (in Dutch)

Uit “De Audiciens”, februari 2015: “CI’s (cochleaire implantaten, Red.) volop in ontwikkeling.

Het is een traditie, de refereeravond van KNO/Centrum voor Audiologie en Hoorimplantaten (CAHIL) in het LUMC op de tweede donderdag van het jaar.

Ook op 8 januari 2015 zit de collegezaal weer vol. Het is dan ook een bijeenkomst waar een aantal disciplines uit de hoorbranche samenkomen. KNO-artsen, audiologen, akoepedisten, audiciens, fabrikanten en anderen luisteren naar voordrachten die inzicht geven in nieuwe ontwikkelingen op audiologisch gebied.

De avond wordt geopend door prof. dr. ir. J.H.M. Frijns, hoofd CAHIL. (…) In het kader van de Medical Delta (een samenwerkingsverband tussen het Erasmus MC in Rotterdam, de TU Delft en het LUMC in Leiden voor de ontwikkeling van medische technologie) is er een presentatie van Johan de Vos die als arts-onderzoeker KNO onderzoek verricht naar nieuwe technologie voor cochleaire implantaten. Onder begeleiding van Wouter Serdijn en Paddy French hebben drie promovendi van de TU een meetversterker (Cees Jeroen Bes), een elektrode ontwerp (Nishant Lawant) en een stimulatorchip (Wannaya Ngamkham) ontwikkeld. Deze technologie wordt onder leiding van Johan Frijns en Jeroen Briaire in het LUMC geimplanteerd en getest door Johan de Vos. Tevens ontwikkelt het LUMC nieuwe meetmethodes voor het terugmeten van de respons van de gehoorzenuw (Dick Biesheuvel).”

Lees meer hier.

A 0.042 mm^2 programmable biphasic stimulator for cochlear implants suitable for a large number of channels

ArXiv-paper on miniature neurostimulator circuit

Today we published the following (scientific) paper online:

A 0.042 mm^2 programmable biphasic stimulator for cochlear implants suitable for a large number of channels
W. Ngamkham; M.N. van Dongen; W.A. Serdijn; C.J. Bes; J.J. Briaire; J.H.M. Frijns;
January 29 2015. 


This paper presents a compact programmable biphasic stimulator for cochlear implants. By employing double-loop negative feedback, the output impedance of the current generator is increased, while maximizing the voltage compliance of the output transistor. To make the stimulator circuit compact, the stimulation current is set by scaling a reference current using a two stage binary-weighted transistor DAC (comprising a 3 bit high-voltage transistor DAC and a 4 bit low-voltage transistor DAC). With this structure the power consumption and the area of the circuit can be minimized. The proposed circuit has been implemented in AMS 0.18µm high-voltage CMOS IC technology, using an active chip area of about 0.042mm^2. Measurement results show that proper charge balance of the anodic and cathodic stimulation phases is achieved and a dc blocking capacitor can be omitted. The resulting reduction in the required area makes the proposed system suitable for a large number of channels.


current generator, current source, current mirror, output impedance, stimulator
circuit, current stimulator, programmable stimulator, biphasic stimulation, neural stimulation, cochlear implants, electrode-tissue interface, electrode-tissue impedance, switch array, charge error, charge balancing, neurostimulator.

A new name, but Biomedical Electronic remains

Biomedical Electronics Lab

Dear Reader,

The Biomedical Electronics Group underwent a small name change. From now onwards, the group is called “The Biomedical Electronics Laboratory”.

Its mission is “to provide the technology for the successful monitoring, diagnosis and treatment of cortical, neural, cardiac and muscular disorders by means of electroceuticals.”

To this end it conducts research on, provides education in and helps creating new businesses in neuroprosthetics, biosignal conditioning / detection, transcutaneous wireless communication, power management, energy harvesting and bioinspired circuits and systems.

First implantation of a vestibular implant

Today it was reported in ‘De Volkskrant’ that doctors of Maastricht University Medical Center have succeeded in, for the first time ever, implanting an artificial balance organ, a vestibular implant, in two patients. A vestibular implant is more or less a cochlear implant that relays information on orientation and accelleration onto the hair cells in the vestibula, the small organ attached to the cochlea that assists in preserving balance. According to Prof. Robert Stokroos of UMCM, the first measurements after the surgery showed positive results. Very important, as far as I understand, will be whether the vestibular implant will allow for perfect integration of the balance information delivered by the implant and the balance perceived by the eyes.

Despite all this, I believe we have exciting times ahead for the application of novel neurostimulating devices.


Mission Possible

In order to present the Biomedical Electronics Group of Delft University of Technology to a couple of companies, it made sense to reveal our mission statement. So here it goes…

The mission of the Biomedical Electronics Group of Delft University of Technology is "to provide the technology for the successful monitoring, diagnosis and treatment of cortical, neural, cardiac and muscular disorders by means of electricity." In order to reach this goal we investigate and design circuits and systems for electrical stimulation, ExG readout, signal specific analog signal processing, power management/conversion, energy harvesting and wireless communication, to be applied in future wearable and implantable medical devices, such as hearing instruments, cardiac pacemakers, cochlear implants and neurostimulators.

So how about that? Reactions are welcome via this blog.


I’m back!

After one year of absence since I graduated for my master thesis, I can happily tell you that I’ m back :). On September 1 I started my PhD research on neural readout circuitry in cochlear implants.

The project is a collaboration between Delft University of Technology and Leiden University Medical Center and is funded by STW (Dutch Technology Foundation). It is called ReaSONS (Realtime Sensing of Neural Signals). Within this project we aim to develop new technology to record the evoked Compound Action Potential (eCAP) generated by the hair cells in the cochlea.

As soon as I have my first results I will let you know. Stay tuned!


Smaller can be better

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 (VI 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’ 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 😀


[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

Is darkness only all blind people can see?

Doing research on neural recording & stimulation that are dedicated to recovering human senses, a question like this may come to your mind: "between loss of hearing and vision loss, which one will make me suffer the most"

It’s a difficult question to answer…and for sure noone wants to experience it. But let’s see what famous people say…

Beethoven stated that "….for me there can be no relaxation in human society; no refined conversation, no mutual confidences. I must live quite alone and may creep into society only as often as sheer necessity demands… Such experiences almost made me despair, and I was on the point of putting an end to my life…"

Helen Keller wrote "…I am just as deaf as I’m blind. The problems of deafness are deeper and more complex, if not more important, than those of blindness. Deafness is much worse misfortune. For it means the loss of the most vital stimulus — the sound of the voice that brings language, sets thoughts astir and keeps us in the intellectual company of man." 

Three, my favourite Dutch band 😉 sings in their song ‘Way back from the Hague‘ that "Silence came over me!!!!"   …and " Darkness is all I can see."

Caraboa, the most famous Thai rock band also has a song dedicated to a blind musician called ‘Wanipok‘. In short it says (interpreted by me): ‘when my eyes are covered by darkness, my life is still illuminated… by music.’ 

For me, silence will isolate us from the society and this will lead us to a deep loneliness. Sometimes… just listening to songs, beautiful scenes can occur in our minds. Is the brain playing tricks on us? Or does it imply that losing sense of hearing is more severe than being blind and darkness is not what blind people can only see.

On March 18th, there will be the 2nd ELCA music festival in the EWI student pub Pub, at TUDelft. The Biomedical Group’s band will perform Wanipok, a cover, and many other songs. I really look forward to that 🙂

Cochlear Implants: A message from patients to researchers

From the information below I feel that as researchers we need to develop cochlear implants (CIs) further. This I consider my duty!!

cochlear Ltd.From "Events and Research in Speech, Language, and Hearing Disorders":

CI user’s mom said "I have a baby with CI and I wish researchers can find a very reliable way to do totally implanted CI, because I think people need hearing always and in each condition."

"I feel that we are placing to much hope into the development of a completely internal implant being released in our lifetime. I have a son who has bilateral implants and it would be amazing if he could swim, bathe, sleep and have sound during these activities. But the fact that he can have sound all of the other time is a modern-day miracle and we are so thankfull to all people putting in endless hours of research!"

"I’ve been fitted with a cochlear implant for about a year and still can’t really enjoy music. Will a new fully implantable one improve the sound quality and enable people to hear music?"

Cochlear Implant Swimming Youtube Video, Click here:

CI user’s mom said "Thanks for this video. Since I watched this video, I have taken my daughter swimming a lot more and she enjoys it way more than before. Before we would spend about 5-10 minutes in the pool. Now she wants to spend all day."