Convert square wave to sine at 2.5 MHz

Thread Starter


Joined Apr 27, 2014
Hi! My cochlear implant (Cochlear Spectra 22) is getting old and the new models are junk - sound quality is horrible - so I want to build my own. I've read and verified that the basic signal frequency is 2.5 MHz (see attached figure), and I can generate this frequency using an SI5351 (*1). The way the implant gets power is via AC to the inductor on the skin side. The pulses also act as code to indicate which internal electrodes to fire off and duration. At first glance, I'm thinking I'll use an mcu (*2) to process the sound and generate the signals. As needed, I'll route the clock signal to the inductor, modified to match the signaling code, since it's not a constant wave. However, I'm not sure how to convert the square wave to a sine. I tried a simple RC filter that I found with a google search, but it looks more like a sawtooth than a sine. I also read about the MAX297 in The Art of Electronics, but that looks like it maxes out at 50KHz. Any other suggestions?

Signal profile: Screen Shot 2018-12-18 at 6.58.56 PM.png


Joined Mar 24, 2008
I have approved this post , but if this a prelude to spamming. Spam is an automatic ban for this site. Good luck with you project. The links you posted triggered AAC auto-moderation routine.


Joined Jun 4, 2014
An LC circuit tuned to 2.5MHz would do the job. You might have to experiment to get the right Q so you don't remove the modulation too.