Warning: The IST cannot activate when its stimulus leads are in electrical contact. Make sure the resistance between the leads is always greater than 100 Ω.
[07-DEC-19] The Implantable Stimulator-Transponder (A3036) is a wireless electrical stimulator that receives commands and responds with acknowledgements, battery measurements, and synchronizing signals using a single antenna. The displacement volume of the A3036A is only 0.90 ml. The electrical stimulus is delivered through two silicone-insulated helical wires terminated with miniature pins. A single radio-frequency command initiate an arbitrarily long stimulus. When combined with the A3036IL series of implantable lamps, the A3036 provides optogenetic stimulus. When combined with a bipolar depth electrode, the IST provides direct electrical stimulus. Between implants, we can recharge the IST's battery through its stimulus leads with the help of a Battery Charger (A3033A).
In its standby state, the IST is ready to receive commands, but is doing nothing else. Its standby current consumption is only 7 μA, so the A3036A, with its 19 mA-hr battery, can remain in its standby state for 2700 hrs before its battery is exhausted. Commands arrive from a transmitter such as the 915-MHz Command Transmitter (A3029C), which we control with the same software we developed for the Implantable Sensor with Lamp (ISL). This software operates with our LWDAQ data acquisition hardware. The IST transmits its acknowledgements and metadata at 915 MHz also, for detection by a data receiver such as the Octal Data Receiver A3027E. The IST transmissions use the same protocol as our Subcutaneous Transmitter System (SCT). The IST command transmissions take tens of milliseconds, and during command transmission, SCT samples will be lost.
The gold-plated pins on the end of the IST's lamp leads mate with a pair of sockets on the A3036IL implantable lamps. The table below gives the available and planned versions of these lamps.
(mW at 20 mA)
|A3036IL-A||C469EZ500||Flat Epoxy||460 (Blue)||20||Available|
|A3036IL-B||C527EZ500||Flat Epoxy||527 (Green)||10||Available (8-wk lead time)|
|A3036IL-A8||C469EZ500||450 μm Dia Fiber, 8 mm long||460 (Blue)||10||Available|
|A3036IL-B8||C527EZ500||450 μm Dia Fiber, 8 mm long||527 (Green)||5||Available (8-wk lead time)|
|A3036IL-C||C460TR2227||Epoxy Dome||460 (Blue)||20||Available March 2020|
|A3036IL-D||C527TR2227||Epoxy Dome||527 (Green)||10||Available March 2020|
|A3036IL-C6||C460TR2227||270 μm Dia Fiber, 6 mm long||460 (Blue)||10||Available March 2020|
|A3036IL-D6||C527TR2227||270 μm Dia Fiber, 6 mm long||527 (Green)||5||Available March 2020|
|A3036IL-E||LXZ1-PA01||Epoxy Dome||660 (Deep Red)||15||Available January 2020|
All ISTs that drive implantable lamps are equipped with a lithium-polymer battery. No other miniature battery can provide 20 mA for the lamp. The IST applies its battery voltage to the lamp through its lamp leads. The resistance of the lamp leads limits the LED current, and we make this resistance part of the design of the device. The average voltage of lithium-polymer battery during its lifetime is 3.7 V. The forward voltage of the blue EZ500 LEDs at 20 mA is 2.9 V. The forward voltage of the green EZ500 and both the blue and green TR2227 LEDs is 3.1 V at the same current. Suppose we choose the resistance of the leads to set the lamp current at 20 mA for battery voltage 3.7 V. The 19-mAhr battery of the A3036A will provide 57 minutes of continuous light output. If our stimuli consist of 10-ms pulses at 10 Hz, the A3036A can deliver a total of 570 minutes of stimulus before it exhausts its battery.
The A3036IL implantable lamps use a variety of LEDs, such as the blue and green TR2227, the blue and green EZ500, and the deep red Luxeon Z. All A3036ILs are equipped with a hypodermic tube on the opposite side of the LED to allow the lamp to be located and held securely during imlantation. The tube is thinned near its base, so it may be cut more easily after the lamp has been secured with dental cement. The optical fibers we use with our implantable lamps are polished at the base and tapered at the tip. We glue the base to the surface of the LED and the fiber captures roughly half the light emitted by the LED and carries it to the tapered tip, wher the light is emitted in all directions. These are our Fiber-Coupled Implantable LEDs (FC-ILEDs).
With no optical fiber glued to the LED, the LED is instead covered with clear epoxy so that it may be placed in contact with the tissue to be illuminated. The surface of the epoxy may be flat or domed, but this makes little difference to the power delivered to the tissue surface. These epoxy-topped lamps we call Implantable LEDs (ILEDs).
One application of the IST is to implanted it together with an SCT so that stimuli can be generated in response to EEG activity in real time, with the help of the Event Classifier running on the data acquisition computer. Earlier ISL device combined stimulator and sensor in the same device, powered by the same battery, and suffered from lamp artifact. When we separate the stimulator and the sensor into two circuits each powered by their own battery, we find that we eliminate lamp artifact in optogenetic applications. The IST's synchronizing transmission, when enabled, is recorded along with SCT signals, and allows us to obtain perfect superposition of the stimulus pulses and biometric signals.
We first proposed the development of the IST in our IST Technical Proposal. Development of the IST began on 06-AUG-19 with a purchase order from UCL.
The figure below shows how the IST system components are connected together. The IST system is an SCT system with the command transmitter and its transmit antenna added on. Follow the SCT set-up instructions to set up the recording system for IST synchronization and SCT biometric signals, then add the command transmitter as shown below.
Referring to the diagram, we have the following components.
The IST system is compatible with the SCT system, in that we can implant ISTs and SCT in animals that live in the same enclosure, and receive signals from both. Only the ISTs will be able to respond to commands.
The Command Transmitter (A3029) plugs into a Long-Wire Data Acquisition (LWDAQ) system and also receives its own 24-V power input to boost its command transmission power. It acts as a LWDAQ device and transmits commands to implanted ISTs through a Loop Antenna (A3015C), the same type of antenna used to pick up data transmissions from implanted SCTs and ISTs.
The Data Receiver (A3027) plugs into the Long-Wire Data Acquisition (LWDAQ) Driver with Ethernet Interface (A2071). The (LWDAQ) system is a data acquisition system developed for high energy physics experiments and adapted here for neuroscience biopotential recording. The data receiver acts as a LWDAQ device. The LWDAQ Driver (A2037E) connects to the global Internet, your Local Area Network, or directly to your computer via an RJ-45 Ethernet socket. You communicate with the A2037E, and therefore the Data Receiver, via TCPIP. On the computer you use for data acquisition, you run the LWDAQ software, which you can download from here. In particular, you use the Recorder Instrument, the Neuroarchiver, and the ISL Controller Tool.
The ISL Controller allows you to send XOn and Xoff commands to individual ISTs. These turn on the IST's synchronization signal, which appears in the SCT recordings as a signal with the IST's channel number, but its content is a square wave in which HI pulses indicate that the lamp is on. This signal allows us to confirm that the lamp was stimulated while looking through recordings, and makes it easier to determine if the stimulus is causig artifact. The synchronizing signal consumes one hundred extra microamps of current, which is insignificant during a stimulus, but will drain the IST battery between stimuli, so we recommend use of the synchronizing signal only during stimuli.
The IST is managed by a field-programmable gate array (FPGA) in a 2.5-mm square package, the XO2-1200. This device provides both volatile and non-volatile memory as well as thousands of programmable logic gates. It is capable of implementing arbitrarily-complex stimuli in response to a single command. The A3036A uses the same firmware as the Implantable Sensor with Lamp (A3030E), in which a single stimulus consists of a set number of pulses, each of fixed length, generated at regular intervales, or at random intervals with a known average value.S3030A_1: IST Schematic.
Each version of the IST has a nominal battery capacity. The A3033A battery is nominally 19 mA-hr. We discharged and charged the battery of device A215.10 five times, and charged once more with an A3033A. Once charged, it reported battery voltage 4.3 V when inactive. We attached a white LED, turned on lamp power continuously and measured 20.0 mA current with the battery reporting 4.1 V. The lead resistance is 56 Ω. The LED forward voltage drop is 2.98 V. We turned on a 50% stimulus ofd 2-ms pulses at 250 Hz and recorded battery voltage versus time.
Part-way through, we measure 11 mA current with the lamp turned on continuously, and the battery is reporting 3.6 V, which is also consistent with LED forward voltage 3.98 V. Thus we are able to calculate the LED current for intermediate battery voltages, and accumulate to obtain the total charge delivered by the battery versus time.
Our fiber tapering machine uses two motor controllers, two micrometer stages, a vertical mounting stand, and a heating coil to stretch a fiber where it is softened with heat and create two tapered ends. One end is the one we keep.
The tapering process moves the base of a 150-mm length of fiber up into a heating coil, stops, and pulls the top portion of the fiber away to create the taper. We follow these steps.
More details of the tapering process are given in the comments of the Tapermaker.tcl file, which you will find in the Tools directory of LWDAQ 9.1.8+.
[18-NOV-19] The A3036AV1 needs the following modifications.
For the A3036B we are going to make the following enhancements to the circuit.
[23-AUG-19] Schematic complete. Arrange components on 10-mm × 10 mm circuit board, narrowed at the top to fit into the terminal end of our 19-mAhr LiPo battery. The A3036 crystal radio uses the SMS7630079LF detector diode in a 1.7-mm long SC-79 package. The threshold comparator is the same MCP6541 but in the smaller SC-70-5 package. The stimulus and battery-check switches are two N-channel enhancement mode mosfets provided by a DMG1024UV in a 1.7 mm × 1.0 mm SOT-563 package. The OR gate is is the same SN74AUP1G32, but in the much smaller UDFN-6 1.0 mm × 1.5 mm package, which we use on our A3028GV1 circuit boards. This package fails to load properly in roughly 1% of assemblies and is impractical to replace by hand, but it is small. The logic chip is the same LCMXO2-1200ZE, but in a 2.5 mm square WLCS-25 package with balls on a 0.4-mm pitch. We are not yet sure how to make a footprint for so fine a ball pitch.
[04-SEP-19] The IST uses the LCMXO2-1200ZE in a WLCS-25 package. The WLCS-25 has twenty-five balls on a 0.4-mm (15.7-mil) pitch. With 10-mil diameter pads the clearance between pads is only 6 mil, which is barely enough to run a 2-mil track, let alone the 5-mil tracks of our usual fabrication process. We consult with Epectec for a solution to the layout problem. They propose that we use 12-mil pads with 10-mil soldermask opening and a 4-mil laser-drilled microvia from the top copper (L1) to the first middle copper layer (L2).
The second layer of copper (L2) has 10-mil pads to receive the 4-mil microvias, as shown below.
There are no pads for the 4-mil holes on the remaining four copper layers: ground plane (L3), power plane (L4), middle copper (L5) and bottom copper (L6). But our drill file specifies 4-mil holes, and we see these rendered in the plot below.
We could have routed tracks directly beneath the microvia holes, but our layout software is incapable of understanding drill holes that pass between only two layers. So we kept the bottom four layers clear of copper around the drill holes. In order to generate the gerber files for the bottom four layers, we deleted the 4-mil vias temporarily.
[06-SEP-19] Completed draft version of P3036A01 firmware, including battery voltage measurement by timing how long it takes to charge up C4. When we request a battery measurement, the firmware will assert BT, which closes the battery test switch U3-6 to U3-1. Capacitor C4 starts to charge through R1 and R2. These resistors present a voltage source 80.5% of VB through a resistance of 6.43 kΩ. Capacitor C4 is 1.0 μF. The charging time constant is 6.4 ms. The BTV signal connects to an input on U8, a 3.0-V logic input with logic threshold around 1.5 V. When VB = 3.6 V, voltage BTV will take around 3 ms to reach 1.5 V, or 100 cycles of our on-board 32.768 kHz clock. To the first approximation, time taken is inversely proportional to the battery voltage, so we expect 86 periods when VB = 4.2 V and 106 periods when VB = 3.4 V. Submit A303601A Rev 1 printed circuit board for fabriction on a ten-day turn.
[30-SEP-19] We have the A303601A printed circuit boards, quantity 100, in panels of 10 each. We solder a battery to a blank circuit board, and a charging connector. We succeed on the fourth battery, having figure out how to fold the battery tabs, solder them to the pads on the circuit board, and press the board into place. One of our 0-V connections is missing due to a bug in the way our PCB layout software implements relief connections to the ground plane. We find we can correct this error with a short wire link.
Once the programming extension is clipped off, the battery and circuit will be contained within a 10 mm × 20 mm × 3 mm cuboid. Allowing for 0.5 mm of epoxy and silicone over all surfaces, final volume will be ≤0.92 ml. We are hoping for 0.80 ml. We charge the battery.
[03-OCT-19] We ship components and circuit boards to our assembly house. We have ordered 20 circuits made. We should receive first article in two weeks.
[04-OCT-19] We receive 1254 of C527TR2227 (green ≥10 mW @ 20 mA) and 1777 of C460TR2227 (blue ≥30 mW @ 20 mA). They come on plastic sheets. They are so thin they are transparent.
We ship all the green ones to an assembly company we have contracted to load the dies onto the A303602A printed circuit board, which we submit for fabrication on a 25-day turn.
[11-OCT-19] We have our first three assembled A3036AV1 circuits, No1-No3. We connect D2-1 to U5-2 in order to correct a PCB error and complete the 0V net. When we connect power, current consumption is 7 μA. We see a 3.3-V 32.768-kHz square wave on both sides of R7. The A3036AV1 has no resistor between OND and its two destinations U6-2 and P3-3. If we tie P3-3 to P3-4, we connect a LO output of U8 to a Hi voltage. We remove U6 on No1 and use its pads to connect 3VB to 3VA. We set VB to 3.3 V. On our programming cable, we connect ispEN to VCC. When we plug the programmer into P1, the cable drives PEN Hi so as to enable the JTAG interface. We program U8 repeatedly from our laptop. Once we program U8, we see a 2.8-V square wave on U7-2 and a 1.9-V square wave on RCK. No matter how we configure TP1 and TP2, we cannot change their state. TP1 remains Hi and TP2 remains Lo. We remove U6 on No2 and repeat the above steps, arriving at the same result.
[14-OCT-19] We use the Lattice Diamond Programmer V3.9, instead of the older ispVM 18.0, to program No1. Now RCK is a 3.0-V square wave, and we can program the behavior of TP1 and TP2 as we wish. We add output KEEPER on unused pin B1 and set equal to STBY in the firmware so as to stop the compiler eliminating the power control unit. We had deleted this output when we adapted the A3030 firmware for the A3036. We solder a white LED with 100-Ω resistor to the L+ and L− outputs of No3, and a steel antenna to A. The No3 circuit still retains U5. We place the antenna over a Loop Antenna (A3015C) driven with 10 dBm of 910 MHz. With the logic chip erased, XEN is Lo, the RF power causes RP to go Hi, and chip power turns on, after which the erased chip asserts OND, ONL, and XEN, keeping its own power turned on, turning on the lamp, and disconnecting the antenna from the tuner. We connect the programming cable. We remove from our source of 910 MHz. We program the device successfully. Stanby current is 7.4 μA.
We look at the RF power signal on D1-1, which we call VR. We have the A3036AV1 over a source of 910 MHz. When VR reaches 10 mV, RP is asserted and both 1V2 and 3VB turn on. With a Command Transmitter (A3029C) we are able to flash the white LED. When the device receives a STOP command, it flashes its lamp. When 1V2 turns on, OND, ONL, and XEN all rise to about 1.5 V for 1 ms. We enable aknowledgements and the No3 circuit transmits an RF signal. The signal is not received by our data receiver. We have not yet calibrated the RF canter frequency or its modulation clock.
During stimulation, the current in No3 when the lamp is off is 220 μA. We solder antennas and lamps to No1 and No2. These are permanently on because of our removal of U6. Their quiescent current consumption is 150 and 250 μA respectively. This is what we call the "active" current of the device, and we expect it to be around 60 μA. Looking at the Lattice Diamond power calculator, this 200 μA quiescent current is consistent with a failure to turn off the band gap references. We try to calibrate the RF center frequency and the transmit clock, but we find that the ring oscillator is not working. It is being eliminated from the design. We believe we can fix these problems by attention to the firmware, so we will proceed with assembly of another 17 circuits.
We add routing priority for the ring oscillator bits, and the fck divisor bits, see P3036A.lpf. Now the compiler preserves all bits and we see the ring and divisor in the device view. We add frequency estimates for the four clocks. We note that we have SDM_PORT set to the default value DISABLE, which means that outputs DONE, INITN, and PROGRAMN are available for general-purpose I/O. We are using one of these, INITN, for our output XEN.
[16-OCT-19] We are able to persuade the compiler to retain our ring oscillator only if we disable the ring oscillator for some fraction of the time. So we turn it on and off with RCK and route it to TP1 directly on No1. The ring oscillator runs 50% of the time. Current consumption is 5.2 mA. The ring oscillator output has period 8.5 ns, frequency 118 MHz. Instead of running the ring oscillator directly to TP1 we run TCK to TP1 and RCK to TP2. We see TCK with period 201 ns. Current consumption 750 μA. Of this, 150 μA is present without the ring oscillator, so the oscillator consumes 600 μA for 50% of the time, the equivalent of 1200 μA for 118 MHz continuously, or 10 μA/MHz, which compares well to the 11 μA/MHz we observed with the A3030 oscillator.
[05-NOV-19] We calibrate the ring oscillator on No2, one of the circuits that is always on. We have not calibrated its RF center frequency. The transmit clock period (TCK period) is 190 ns, which is on the edge of being too low. But we receive acknowledgements from the device. We study the battery monitor, which consists of U3-2, R1, R2, and C4. When we assert BT, U3-2 turns on, charging C4 (1 μF) through R1 (8 kΩ), with R2 (33 kΩ) present to limit the voltage we attain at BTV, and to discharge C4 between measurements. Eventually BTV reaches the threshold of the Schmitt trigger input on U8-D5, which we have set to have "small" hysteresis. We measure the charging time in RCK periods, which are 30.5 μs. The charging time constant is 6.4 ms, or 200 periods. The A3036A returns the charge time in the data of an auxilliary message on channel 15. We vary VB and transmit battery commands to No2 and plot the charge time versus voltage.
We prepare ISL Controller Tool 6.1, which supports the A3036A battery measurement. We are able to measure the battery voltage with better than ±0.5 V precision around the critical region of 3.6-3.8 V.
[08-NOV-19] We take No2 and remove the wire between 3VA and 3VB. We see 3VB at 0.2 V and 1V2 at 0.0 V. Current consumption from VB is 8.7 μA. We connect 3VB to VB with 1 kΩ using the pins of P1 and P3. We apply 3.3 V to VB. We see 2.3 mV across the 1 kΩ, implying that U8's I/O circuits, U9's shutdown current, and U2's enable input current are together 2.3 μA. We find we can program the board with the 1 kΩ VB to 3VB series resistor in place. When we turn on the lamp, TP2 is asserted and we see 360 mV across our 1 kΩ resistor, which is the current flowing through the 1 kΩ and R13 (8 kΩ). With the lamp off, the total current consumption from VB is 213 μA. The Lattice Diamond power calculators says the core current consumption of U8 when the band-gaps are turned off is 60 μA, which was what our A3030 circuits consumed with almost identical firmware.
We install the Lattice Diamond 3.11.0. We were previously using 2.2.0. In both cases, we select the LSE synthesis tool. We re-create the P3036 firmware for LD3.11 and compile. Total current consumption 220 μA, command reception and acknowledgement working. With fck_divisor = 11 we get TCK period 188 ns, implying ring oscillator 117 MHz. With fck_divisor = 12 we get 220 ns, implying ring frequency 109 MHz. We have some work to do stabilizing the ring oscillator with respect to fck_divisor.
We are using Lattice Diamond Programmer 3.9.0. We discover the TCK Divisor setting. Programming is unreliable with the divisor set to 1. With the divisor set to 2, scanning and programming works every time, but takes twice as long: 123 seconds. Current consumption of No2 remains 224 μA. In order to free up U8 pins A4, B4, A5, and C5 for general-purpose I/O, we have disabled the JTACK interface by default. We now enable the JTAG interface and program again. We remove R1 because BT (TDO) is HI. Current consumption 218 μA.
We turn on the RF oscillator continuously, at the LO frequency. With frequency_low = 7, the center frequency is 909.5 MHz, and with frequency_low = 8, center is at 915.5 MHz. We set frequency_step = 2 and frequency_low = 7 and obtain reception of acknowledgements.
We route the BTV logic signal to TP1. This signal is the voltage BTV at U3-1 passed through U8-D5's Schmitt trigger input. Let's call it BTVL. We look at BT, BTV, and BTVL during a battery test for No1. Battery voltage is 3.58 V. Acknowledgments are turned off, so the only response of the device is the battery message.
We are not receiving acknowledgements from No1. The TCK period is correct, but we have not checked the RF center frequency. We don't have its report of the charge time in RCK periods. But we expect from our earlier calibration that this will be around 120 periods, or 3.66 ms, which is not consistent with the above measurement. The above measurement was performed with this same circuit, but acknowledgments were enabled. We repeat for No2.
We do receive acknowledgements from No2, and it says 172 every time, or 5.25 ms, which is consistent with the the above observation.
[20-NOV-19] We check the response of the A3036AV1 to a −5 dBm sweep applied to an A3015C antenna, duplicating our earlier measurement of the A3030E antenna network. We see no response on VR in the A3036AV1. The A3036AV1 is loaded with D1 = SMS7621079LF, which turns out to be the wrong member of the family. The SMS7621 is designed to measure power from a 50-Ω source, and requires forward biase 300 mV for a current of 1 mA. The diode we are replacing is the now-obsolete HSMS285C, which requires only 150 mV for 100 μA and 250 mV for 1 mA forward current. Its video resistance is 8 kΩ at zero biase. Instead of the SMS7621, we should have used the SMS7630, a zero-biase detector diode with video resistance 5 kΩ, requiring 100 mV for 100 μA and 200 mV for 1 mA forward current. We order these. In the meantime, we supply 10 dBm of RF power to an A3015C loop antenna and place an A3036AV1 on top. Matching network resonance is at 1000 MHz. We add 0.5 pF to C6 and resonance drops to 920 MHz.
[25-NOV-19] We apply +10 dB to an A3015C. We place an un-tuned A3030E circuit board on the antenna and measure VR as we increase frequency from 900-1000 GHz. We see a maximum of 60 mV at 970 MHz. We repeat with A3036AV1 with SMS7621 diode and C6 = 1.5 pF. We see a maximum of 60 mV at 912 MHz. We apply −5 dBm sweep at 10 kHz and see 20 mV peak on the A3030E at around 975 MHz and <2 mV on A3036AV1 at around 915 MHz. Replace D1 with SMS7630, taking care to place the pin 1 marker on the other side of the footprint. We see 20 mV on A3036AV1 at around 915 MHz. The video resistance of the SMS7621 is so high that the diode cannot charge C7 = 100 pF fast enough to respond to the sweep with a 20-mV peak. That of the SMS7630 is 5 kΩ, giving a time constant of 0.5 μs with C7.
[26-NOV-19] We vary the value of the ring oscillator divisor and measure the transmit clock period. We want to see the period increasing with divisor, and we do from 7 to 14, but not at 15. We find that our ring oscillator is being optimized for speed, but not the fast clock divider. When we turn on optimization for the fast clock divider, the TCK period is unstable, so we are leaving the divider without optimization for now.
We connect a Modulating Transmitter (A3014MT) to a Loop Antenna (A3015C). We modulate the RF with a square wave so that it moves in and out of the center frequency of our A3036A with SMS7630 diode. Rise and fall times are around 1 μs.
We select a circuit with D1 = SMS7621 and add 0.5 pF to C6. We repeat the above experiment with this new circuit and our rise and fall times are of order 4 μs. We sweep the A3014MT output frequency with a ramp. We use our SSG-6001 synthesizer and a ZAD-11 mixer to calibrate the sweep on our oscilloscope screen. We connect the sweep to an A3015C that is flat on our bench. We move the A3036A around on the loop until we maximize the peak in VR.
With the SMS7630 diode, we obtain a peak of 40 mV. But with the SMS7621 diode the peak is no more than 10 mV. We add 0.5 pF to C6 and switch D1 to SMS7630 on all remaining A3036 circuits. Peak of sweep response for all ten circuits in the range 903-913 MHz.
We switch the BTV signal input hysterisis from SMALL to LARGE. We set battery_calib in the P3036A03 firmware to 58 and now the battery counter is 200 for VB = 3.70 V. We do the same for No3. In order to calibrate No3 we send command 0081 to the Command Transmitter (A3029C) to turn on RF continuously, which allows No3 to remain on during programming. We have battery calibration 61, which results in battery counter 199 at 3.70 V, 184 at 4.00 V, and 218 at 3.40 V. We use −60 for the scaling factor in V/cnt and our reference will be a count of 200 for voltage 3.7 V.
[27-NOV-19] Inactive quiescent current of No3 and No4 is 7.3 and and 7.3 μA. We program and calibrate No4. We now have 3 A3036A calibrated for battery monitoring, their battery calibration values are 56-61. We attempt to program and calibrate more circuits, but have difficulty programming, and once programmed, they do not respond to commands, not even with an increase in current consumption.
[28-NOV-19] We devise an easier way to connect U5-3 to 0V, by connecting D2-1 to U9-3. This leaves D2-2 free for a wire to look at VR. We start with No6, and succeed in programming and calibrating. We modify No7 and program, but U7 is not producing RCK. We modify No5 and program, but VR is oscillating, spending 90% of the time at 10 mV and rising for 10% of the time to 100 mV, every 70-100 μs, the period varying as we move our finger around the circuit. This behavior is consistent with a matching oscillation on XEN, whereby U4 is connecting the antenna to the tuner only 10% of the time. WEe put a probe on XEN, but the oscillations stop and XEN stays HI, turning on U9, and disconnecting the tuner. Current consumption is 12 mA.
[02-DEC-19] Of 10 A3036AV1 circuits we have corrected with modifications, six are calibrated and ready for battery and encapsulation.
The active current consumption remains roughly 70 μA higher than the 60 μA suggested by the Lattice Diamond power calculator for this design. The same functionality loaded into the A3030E circuit yields active current consumption of around 70 μA.
[03-DEC-19] We have five A3036A programmed with firmware P3036A03 ready for encapsulation, with batteries loaded, 45-mm lamp leads, and 30-mm stranded antennas.
The leads are our 0.7-mm diameter silicone insulated leads, red for L+ and blue for L−. On one device, we measure lead resistance 27 Ω and 29 Ω. We expect 6.0 Ω/cm = 54 Ω. Assuming battery voltage 3.7 V, LED forward voltage drop 2.9 V and lead resistance 54 Ω, we expect LED current (3.7 − 2.9)/50 = 16 mA.
[04-DEC-19] We have 14 of 460-nm EZ500 LEDs mounted to A303602B printed circuit boards. We run 30 mA through each and measure optical power output. We get 25.3±1 mW. This compares well with the average 26.9 mW we obtained with LEDs from the same batch earlier.
[06-DEC-19] We have five encapsulated A3036A. Devices A215.3, A215.4, A215.8, and A215.10 respond to commands, transmit the synchronizing signal, and deliver power to LEDs. Device A215.9 does not respond to commands. We place the four working devices with lamps in our Faraday enclosure with data antenna 15 cm to one side and command antenna 15 cm to the other. We connect boost power to the command transmitter. Reception of commands is unreliable. We place the four devices in a beaker of water. Their bodies rest upon the glass bottom. Reception is now reliable. We turn on the lamps 90% of the time with a continuous stimulus. It takes ten to twenty minutes for the batteries to drop to 3.5 V according to the ISL Controller's battery voltage measurements. We connect 5.0 V to the lamp pins of A215.10 and see 9 mA flowing in.
The re-charge diode is the diode in parallel with the drain of U3-3, see schematic. The recharge current enters through L+ end exits through L− In order to exit through L−, it travels along the 0V net through the re-charge diode. The current through the battery is the total incoming current minus the circuit's inactive quiescent current, which is around 7.3 μA. We want to charge the battery to 4.2 V and then reduce the current slowly to zero while maintaining a battery voltage of 4.2 V. 5.0 V connected to the lamp leads, the voltage across the battery will be 4.2 V when the current flowing through the diode and the 54-Ω lamp leads is 4.0 V. When the current drops to 1 mA, however, the battery voltage will be 4.5 V, which could damage the battery. If we stop the re-charge when the current is 3 mA, we stop it when the battery voltage reaches 4.3 V, which may be okay. But if we set the charging voltage to 4.7 V, the battery voltage will be 4.0 V at 3 mA, 4.2 V at 1 mA, and 4.3 V at 0.1 mA.
We have been charging A215.10 for twenty minutes with 5.0 V and the charge current has dropped to 7.5 mA. We drop the charge voltage to 4.7 V and the current drops to 3.4 mA. We connect all four ISTs to the same 4.7 V source and leave to charge.
[09-DEC-19] We have two A3036IL-A8 prepared. No1 we moved the fiber before the epoxy was cured. No2 we allowed to cure without interference. Today we measure their output power with a photodiode and obtain 2.9 mW for No1 and 4.0 mW for No2. Average LED output at 30 mA is 25 mW, so let us assume 12.5 mW at 15 mA, giving us 23% and 32% coupling efficiency. In earlier work our best head fixture provided 41%, our worst provided 22%, and our median was 38%. Low coupling efficiency was a strong function of the quality of the taper base. These two tapers were both chipped at the base, but only in the cladding, so we trusted that they would work adequately.
[10-DEC-19] We push three of A3036A into a 10-ml graduated tube containing 5 ml of water. The water level goes up to 7.7 ml, making the individual A3036A volume 0.9 ml. We are testing lamps and batteries, and we notice that the lamp flashes when we perform a battery measurement, on both No8 and No10. We have not checked No3 and No4.
[11-DEC-19] We have A3036IL-A8 No3, having snapped the fiber on No2, leaving us with only No1 24% efficient. With 15 mA current into No3 we see photocurrent 0.33 mA, or 4.1 mW for 33% efficiency. We glue the fiber onto No4 and leave to cure. We use our prototype A3033A to charge A3036A No3, No4, No8, and No10 until charge current is less than 1 mA.
[12-DEC-19] A3036IL-A8 No4 emits 3.7 mW at 15 mA for 30% efficiency. And then the fiber fell out of the glue joint. We throw away the glue cartridge, which is three or four years old, even though our glue samles have all set well. We take out a new cartridge that is less than a year old. We set up a new LED No5 and measure power output before applying fiber: 11 mW for 15 mA. We glue a new fiber.
[13-DEC-19] A3036IL-A8 emits 4.0 mW at 15 mA for 36% efficiency. We place an IST A3036A attached to an A3036IL-A in 200 ml of water and move the beaker around on an ALT platform, which is 32 cm by 16 cm, all parts, especially the corners. We try the IST lying flat on the bottom of the beaker, suspended against the side wall, and suspended in the center. We open and close the enclosure door. We send stimulus commands and observe by eye if the IST received the command. Of 100 stimuli, the IST received 96%. The lost 4% were all in one far corner of the platform with the door closed.
We have the IST Prototype system ready to ship: 3 of IST A3036A (A215.3, A215.4, A215.8), 8 of ILED A3036IL-A, 2 of FC-ILED A3036IL-A8, 1 of Command Transmitter A3029C, 1 BNC elbow, 1 Boost Power Supply for A3029C, 4 BNC feedthroughs, 4 short antenna cables, 1 of A3015C with cable, and 1 Battery Charger A3033A. We ship DHL to London.
We have A3036A A215.10. When inactive, battery measurement is 4.2 V. When active, 4.0. We start a 10-Hz, stimulus of 30-ms pulses. After 9 minutes, battery reports 3.9 V, after 17 minutes, battery reports 3.8 V. We stop stimulus, battery reports 4.1 V.
[16-DEC-19] Continue 30% stimulus with A215.10. We note that frequency of stimulation, as seen in Neuroarchiver spectrum of synchronizing signal, is 10.25 Hz, not the 10 Hz wer requested. After a total of 58 minutes since start of drain, battery reports 3.7 V. We stop stimulus, battery reports 3.8 V.
[17-DEC-19] Continue 30% stimulus with of A215.10. Before start, battery reports 4.0 V, after start, reports 3.7 V, but this rises to 3.8 V after a few minutes. After a total of 76 minutes since start of drain, 3.7 V. After a total of 126 minutes, 3.6 V. We stop, battery reports 3.8 V. Later, we continue for another 33 minutes until the battery voltage has dropped to 3.4 V, and then stop. Total time is now 159 minutes. We connect stimulus leads to 4.7 V.
[18-DEC-19] Disconnect A215.10 from 4.7 V charging voltage. It now reports 4.3 V battery when inactive, 4.1 V when transmitting its synchronizing signal, and 4.1 V when generating 30% stimulus. After 23 minutes, reporting 3.9 V. We now switch to a 1% stimulus: 1 ms pulses at 10 Hz and leave running. After 490 minuts of 1%, reporting 4.0 V.
[19-DEC-19] At 9:21 am lamp still flashing at 1%, battery reports 3.8 V. So far 22 min at 30% and 11 hrs at 1 %. Change to 5%, battery reports 3.8 V.
[20-DEC-19] At 9:13 am lamp not flashing. Cannot get a battery report or acknowledgement from the device. Connect to 4.7 V charger at 9:18 am, charge current 0.01 A. At 9:37 am charge current is 5.6 mA. Disconnect and obtain battery report 3.7 V. Reconnect to charger, 5.6 mA. At 10:33 am charge current is 4.6 mA. At 11:20 am battery reports 4.0 V and charge current is 4.0 mA. At this current, charging diode drops 0.55 V. Assuming leads are 56 Ω, we expect VB = 3.93 V. At 15:27 charge current 0.7 mA, reports 4.2 V. Start 50% stimulus, battery reports 4.0 V.
[23-DEC-19] Friday and today we get 129 minutes of 50% illumination from A215.10 at which point battery reports 3.4 V. We continue with 10% for 17 minute until battery reports 2.9 V. The lamp still flashes, but we perceive it to be dimmer. Connect to 4.7 V charger and see 11 mA. After 18 minutes 6.0 mA, 27 minutes 5.7 mA, 120 minutes 4.0 mA, 300 minutes 1.1 mA. Remove and connect LED. Battery report 4.2 V. Start 20% stimulation at 15:40.
[24-DEC-19] Our 20% stimulation ended some time before 10:30 am. We charge battery for half an hour, then run 250 Hz 1-ms pulses, after half an hour, battery reports 3.5 V. We attach to A3033A charger at 11:45 am. We have ten more A3036A circuits modified, cleaned, and dried. We are numbering these No4-No13 using the labels on circuit boards. Inactive current 7.47plusmn;0.1 μA for all but No9, which consumes 12 mA and we reject.
[26-DEC-19] We use the Tapermaker Tool to make tapered optical fibers using our new 270-μm diameter high-index glass fiber, with numerical aperture 0.86 and diameter tolerance ±30 μm. We have not bothered polishing the bases of the fibers. We are working on getting a symmertic, uniform taper at the tip.
We are confident we can make 6-mm long fibers with 1-mm tapers at the tip. We can control the length of the taper with the configuration of the tapering process.
[27-DEC-19] We have A215.10 recharged over-night, reporting 4.3 V when inactive. We start 10 ms pulses at 1 Hz for 1% stimulus at 12:30.
[30-DEC-19] Device A215.10 reports 3.5 V at 12:21. The active current consumption of A210.10 is 109 μA, combined with 1% of an average of 15 mA lamp current is 259 μA. So far the battery has provided 18.6 mA-hr.
[31-DEC-19] We enhance our ring oscillator implementation, separating it into its own VHDL file P3036A05_OSC. In P3036A05_Main we specify fck_calib to configure the ring oscillator. The ring oscillator output is FCK, which we route to TP1. We no longer route TCK to TP1 because we encounter timing and routing issues when we do so.
We calibrate A215.17-19. We have enhanched the ISL Controller to accommodate higher channel numbers. For fck_calib = 17, we are making a ring oscillator containing nine gates, and dividing its frequency by six. The result is an FCK period of 99 ns. The single-gate ring oscillator would run at 545 MHz. A single gate delay is around 1 ns.
We try various alterations to the power controller firmware in the hope that we can reduce the standby current consumption to 60 μA, but our standby current consumption for 17-19 is 154, 143, and 116 μA with only slight variations regardless of firmware.
[03-JAN-19] We complete calibration of nine more A3036A taken from our second set of ten. There were no hardware issues with these devices except for 12 mA inactive current in one circuit. Calibration constants and current consumption shown below.
The average difference between the Xmit and Active current ius 93 μA with standard deviation 4 μA. The slope of current versus sample rate, dI/dS, is 0.091 μA/SPS, which is less than the 0.11 μA/SPS we observe in the A3028GV1 circuits. Our concern remains the average active current, which is 160 μA with standard deviation 30 μA when we expect 70 μA with standard deviation 3 μA.
[06-JAN-20] Take A215.25, place on RF power. Current 179 μA. Connect P1-4 to P1-7, making sure PEN is unasserted. Current 180 μA. VB = 3.7 V, 3VA = 3.0 V, 1V2 = 1.2 V. Immerse entire circuit in acetone. Place in vacuum chamber, evacuate, allow to boil for ten seconds, remove, blow dry. Current 169 μA. Start stimulus with a flash every three seconds. Cool U8 with freezer spray. Current drops to 25 μA and lamp is still flashing. We cool again, then attach a thermocouple and record current with temperature as the device warms up.
[07-JAN-20] We shatter the corner of U8 on A215.24. We heat U8 from above with iron at 400°C. After twenty seconds, it comes loose. We load another WLCSP-25 package by hand, heating from above with iron at 400°C. After ten seconds, the package attaches. We heat for another ten seconds. We wash and dry and the new U8 programs first time, and operates with the same calibration constants except we must drop battery_calib from 72 to 57. Active current consumption 150 μA.
The U8 on A215.24 may have been damaged by heat when we loaded it at 400°C. But it was not damaged by handling. We held it with tweezers. We measure the variation in current consumption with temperature and add to the above plot. The U8 on A215.25 may have been damaged by machine placement. But it was not damage by temperature. The reflow temperature profile is here, and reaches only 247°C for four seconds.
Summary of failures for B88120, 20 of A3036AV1, 4 faulty circuits. 2 with short or open circuit under U6. 1 with U7 not producing RCK. 1 with open circuit under U8. We replace U8 on this last one and produce fully-functional A215.26. We measure active current versus temperature for an A3030E, E157.1, and plot.
[09-JAN-19] We have 5 of A3036IL-C blue TR2227 and 5 of A3036IL-D green TR2227 back from Palomar Technologies. We connect 5 V through 200 Ω expecting 10 mA to flow into each LED and see of order 15 mW of light from blue LEDs and 6 mW from green LEDs. Some emit no light, some emit a flickering dim light, some emit a steady dim light. We pick a blue one and measure current and power output versus applied voltage. At each measurement, we connect power, make our measurements quickly, and disconnect power so as to allow the LED to cool down.
The plot below is taken from the TR2227 data sheet. The optical power output is, to the first approximation, proportional to the current. Our plot shows the optical power increasing with voltage as suggested by the data sheet. But the forward current does not agree with the data sheet. At 3.5 V, for example, the forward current in our prototype is 120 mA, while the data sheet suggests 30 mA. The data sheet suggests 45 mW of blue light for forward voltage 3.5 V, but we see only 12 mW.
We try cleaning one board with hot water and a brush, but the LED comes off. We knock another off by accident. When we apply 7.0 V through 200 Ω, all eight remaining LEDs emit light, some dim, some bright. Forward current is 75 mA for the six bright ones and 90 mA for the two dim ones. We measure the resistance between the input terminals. One of the bright green LEDs has resistance 2 kΩ in both directions. One of the bright blue LEDs has resistance 300 kΩ in both directions. Among the rest, the resistance varies 10-100 kΩ, the same in both directions, with no correlation between brightness and resistance.
[10-JAN-20] We equip A215.26 with two 120-mm long leads, OD 0.8 mm, 6-mil wire, MDC26398 spring. Lead resistance 19.6 amnd 19.8 Ω. We connect to an A3036IL-A and power from benchtop supply through ammeter. We measure VB at the circuit board. We turn lamp on to full power continuously. We measure total current versus VB.
The inverse slope of the graph is 44.5 Ω. We repeat with A215.25 with two 50-mm long leads, OD 0.7 mm, 4-mil wire, MDC13867A. Lead resistance 28.2 and 27.0 Ω. The inverse slope of the graph is 63.9 Ω.