Prompt Acknowledgment

The Implantable Sensor with Lamp (A3030C) for ISL6 provided acknowledgment messages in response to acknowledgement request instructions from the Command Transmitter (A3029B). The transmission of these acknowledgements was, however, delayed by up to 2 ms after the A3030C processed the acknowledgment request. This meant that the best synchronization we could obtain between lamp pulses and the recorded X signal would be ±1 ms. One of our objectives for ISL7 is to improve the precision of the lamp and recording synchronization.

The Implantable Sensor with Lamp (A3030D) for ISL7 transmits an acknowledgment a fixed 60 μs after it processes a request. The ISL Controller V4 requests an acknowledgment immediately before it initiates a stimulus cycle, so the delay between the reception of the acknowledgment and the start of the first light pulse of the stimulus is deterministic. The figure below shows the delay for 100-Hz pulses.


Figure: Prompt Acknowledgment Timing with Respect to First Lamp Pulse. Top trace has a 60-μs pulse marking the moment the acknowledgement is transmitted. Bottom trace has a longer HI interval that marks the start of the first light pulse.

For a 10-ms interval (100-Hz pulses), the delay is 750 μs. When we increase the interval length to 100 ms (10-Hz pulses), the delay is 6.3 ms. The delay is a fixed 150 μs plus 2/33 of the interval length. The A3030D's prompt acknowledgments should allow us to synchronize stimulus and recording within a fraction of a millisecond.

ASIDE: While working on the prompt acknowledgments, we discovered that the A3030's radio-frequency oscillator, which is the same oscillator we use in our subcutaneous transmitters, needs roughly 50 μs to stabilize when it has been inactive for more than 100 ms. When transmitting at 512 SPS, the oscillator is never inactive for more than 2 ms. But in the ISL, we can request acknowledgment even when the data transmission is disabled, and in that case, the A3030C of ISL6 did not allow sufficient time for the oscillator to stabilize, so that acknowledgments were unreliable when data transmission was turned off. In the ISL7 we turn on the oscillator 60 μs before any acknowledgment transmission, and we get 100% reception of acknowledgments under all circumstances in a faraday enclosure.