Development of a Wireless High-Frequency Microarray Implant for Retinal Stimulation - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 184

marked as SIG. This common bus carries the time-multiplexed signals of all
the probes. PCK is the clock for DFF1 to DFF32 connected in a ring, while Q
of DFF32 is the clock for DFF33 to DFF64 connected in another ring. DFF1
and DFF33 are designed with set input, while the rest with reset input. When
SYN is made low, DFF1 and DFF33 are set and the rest of the DFFs are
cleared selecting probe P0101 and initiating the stimulation process beginning
with P0101. With the rising edge of next clock cycle P0102 is selected, and
so on till the 32nd clock cycle. At the rising edge of 33rd clock cycle, Q
of DFF32 switches from low to high clocking row decoder. With that, 2nd
row is selected and stimulation proceeds with P0201, P0202, etc. This pattern
goes on till the end of 32nd row and 32nd column. So we see the stimulation
progresses from left to right and from top to bottom of the array and it progresses
with the rising edge of the clock. Each probe is sequentially selected at each
rising edge of clock resetting the previous one. After the 32 32nd clock cycle,

SYN is made low again to force the decoder to point to the beginning of the
array for synchronization. For retinal stimulation, data is sent in multiplexed
fashion. Upon sending the SYN pulse, the first data corresponding to P0101
is sent, followed by P0102, in sequence from left to right and from top to
bottom of the array. For retinal response monitoring, the multiplexed signal
is decoded. Upon sending the SYN pulse, the first decoded data corresponds
to P0101, followed by P0102, etc. in the same sequence as in stimulation.

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Experimental Results

Figure 9.16 shows the microscopic view of 32 32 array RS fabricated using

0.5 m CMOS technology. For testing, RS is fabricated without package, and
tested by microtest probes under microscope. We have also fabricated it in
package specially designed for testing. Typical 10K neural impedance is
used as load. Test result of RS as a stimulator is presented in Figure 9.17a.
We have presented here the output of probes P0201, P0202, and P0203
only. These three probes are consecutive probes. We have excited them
by biphasic waveforms. Their stimulations are one cycle apart. The result
shows that each probe was excited for the duration of one clock cycle by
the biphasic waveform. We have tested it for other experimental waveforms
and found that it stimulates the neurons as expected. This means that RS
is capable of stimulating the neurons sequentially by any kind of analog
waveforms.
The RS has also been tested as reader (Figure 9.17b). In this test, we have
applied 0.5 V AC signals of different frequencies to the probes simultaneously
and monitored the output on output signal (SIG) line. Here we have presented
the result for probes P0201 and P0202. P0201 was excited by 1 KHz sinusoidal
signal and P0202 by 4 KHz sinusoidal signal. The SIG came out multiplexed.
This signal can be sent out through reverse telemetry.

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