I received a press release recently for an IC that is intended for use in implantable nerve stimulation devices. This caught my eye for a couple of different reasons.
The first has to do with the market for which it is intended — medical device manufacturing. In my career, I've worked for two different companies making medical diagnostic equipment. I've also sold ICs to similar companies. It's good work to do, because you end up being directly responsible for improving people's lives (so, good karma).
The second reason this caught my eye is because I've known people — friends and relatives — who could have benefited from such a device, both for pain management and for mobility.
The IC (CSI021 from Cactus Semiconductor) is a quad programmable pulse generator. Each generator is a current source/sink, capable of sourcing 6mA and sinking 1.5mA into as low as a 1.5kΩ load (i.e., you). They accomplish this by boosting the battery voltage to 18V so the circuitry has plenty of compliance voltage for higher impedance loads. The pulses are capacitively coupled to facilitate sourcing and sinking current.
In an actual application, you would use one or more of the stimulator ICs, a microcontroller, a rechargeable battery, power supply circuitry, and suitable RF tank circuits. Connections for recharging and for the data transfer must be done non-galvanically for safety reasons. Both are done via RF links — hence the need for the two tank circuits. These two wireless links allow the IC plus its associated circuitry and PC board to be implanted. Here's a block diagram showing an 8-channel stimulator:
Clearly a simple design that should be easy to construct and evaluate. But more on that in a moment. Here's a closer look at the IC:
What's interesting here is the inner workings are quite straightforward. It contains current sources, analog switches, DACs, some logic to control timing/pulse generation, and an SPI interface. You could build this in your basement lab. But, you'd have trouble squeezing it down to 4mm square. So an obvious advantage of using the IC is that you can then concentrate your engineering time on the V&V (verification and validation) of the systems software, firmware, and hardware.
Anytime you work on a medical device (evaluative, diagnostic, or implantable) you will need to document every step of the process from the product's inception through the design and marketing stages and on to the point of clinical testing and shipping products. This is not the usual commercial product timeline where you dream it up on Monday and start shipping on Friday.
Also worth noting is that the IC could see use outside of medical apps — it is at heart a 4-channel programmable current source/sink. You can probably think of other applications. If you do, please tell us about them.
Have you worked on any projects that you felt especially good about, that gave you that warm, karmic glow? Let us know in the space below.