EEG Monitor Incorporated

We have our first Implantable Sensor with Lamp (A3030B) with functioning EEG amplifier and transmitter. The circuit includes the same Command Receiver and Lamp Power Supply as the existing A3030A, but we have now loaded the amplifier, ADC, radio-frequency oscillator, transmit antenna, and electrode leads. In order to get the digitization and transmission working, we translated our existing data transmitter firmware from its original ABEL to the more modern VHDL required by the A3030B's CPLD. The graph below shows the frequency response of the amplifier as observed in the Recorder Instrument after digitization at 512 SPS, transmission at 902-928 MHz, and reception in by loop antenna in a faraday enclosure.



Figure: Amplitude versus Frequency for 11-mV pp input on X. We see the bump in gain at around 130 Hz, which is a characteristic of our three-pole Chebyshev low-pass filter.
We turn on and off the A3030B's 915-MHz radio-frequency data transmission with 146-MHz radio-frequency command transmissions. The A3030B is either digitizing and transmitting its analog input, or it is doing nothing with its analog input. We update the ISL Controller Tool to permit us to turn on and off data transmission with the press of a button.


Figure: The Updated ISL Controller Tool. We now have buttons Xon and Xoff to turn on and off data transmission. We have labels along the top that indicate the status of each of fourteen possible ISLs.
Of particular concern to us was interference between the data transmission and command reception. With data transmission turned on, there was the possibility of the 915-MHz power on the transmit antenna disrupting or stimulating the 146-MHz command receiver. But no disruption appears to occur. Command reception is equally effective with simultaneous data transmission.

We are also concerned about the effect of command transmission upon the A3030B's analog input. In an earlier experiment, we observed 20-mV pulses at the analog input in response to command transmission at range 70 cm. The A3030B includes a 40-kHz low-pass filter (R5, R6, and C here) at the analog input, which we expect to attenuate 146-MHz by a factor of 3500. In initial experiments, we are unable to observe any effect upon the analog input by command transmission. We will conduct more thorough measurements in the coming weeks. For now, with 100 μV of mains hum on our un-encapsulated circuit with external battery, we see no effect, so it appears that we have reduced its magnitude to less than 100 μV.

Only one A3030B exists today, which we made entirely by hand. We have ordered another thirty to be assembled by machine and shipped to us by the end of October. Of these, we will use 5, 5, and 10 to fulfill ISL Development Stages 5, 6, and 7 respectively.