ISL Prototype in Development

We are assembling and testing our prototype Implantable Sensor with Lamp (A3030). For details of development, see the manual. For circuit diagram, see S3030_1. The device combines an Implantable Lamp (A3024) with a single-channel Subcutaneous Transmitter (A3028B).


The A3030's logic chip contains enough programmable logic to implement a microprocessor, enough working memory to record several seconds of EEG, and enough non-volatile memory to retain its operating instructions. Our first implementation of the A3030 will provide only basic logic functions, such as decoding commands and generating trains of optical pulses. But in the long run, we plan to build a microprocessor in the logic chip. The A3030 provides a TQFP-100 footprint for the logic chip, which is 14 mm square. Future ISL devices will use the WLCSP-25, which is 2.5 mm square. Being a prototype circuit, we wanted to be able to make the A3030 by hand. The WLCSP-25 package is a 0.4-mm pitch BGA, which would be very difficult for us to load by hand.

The A3030's lamp power supply is almost identical to that of the A3024, except that it includes a switch to modulate the LED current at 5 MHz so as to dim the average power output without losing efficiency, and without producing any electromagnetic noise that would be picked up by our EEG monitor.

The command receiver uses the same split-capacitor tuning network as the A3024, except we now have a dual tuning diode to give us double the received signal amplitude. We hope this additional diode will increase the operating range of command transmission.

The EEG monitor is similar to the one in the A3028. It provides one channel with gain ×100 and cut-off at 160 Hz. To isolate the amplifier input radio-frequency noise and LED switching noise, we have a low-pass filter in front of the input, as we proposed earlier.

The A3030 has no magnetic sensor with which to turn on and off. We will switch it on and off with 146-MHz RF power through its Command Receiver. Each command transmission will activate, at least temporarily, all devices within range. After the command, some devices may remain awake, others may go to sleep, depending upon the commands transmitted. We will activate the EEG transmission through the Command Receiver also. The active current consumption of the A3030 with no EEG transmission and the lamp turned off is around 60 μA, which is much higher than the A3028's 20 μA and the A3024's 2 μA. This higher consumption is due to the higher-capacity logic chip.

The A3030 will be powered by a 382030 160 mA-hr lithium polymer battery. This battery is rechargeable, and we will be able to recharge it up until the time we encapsulate the entire device for implantation. After that, its value lies in its ability to delivery over 200 mA with minimal drop in output voltage.