Retinal Prosthesis Dissertation - Student Home Pages

E.g. choosing a frame rate of 100 gives a spike time of 39.0625ns and a partial spike
time of 9.7656.25 ns from a subset of the table (fps_calcs.xls) used to construct the
above chart.
fps T f T ae (@1024 T ae (ns) T long_pulse T spike_pulse T partial_spike
f pixel
25 0.04 3.906E-05 39062.5 781.25 156.25 39.0625 25600
50 0.02 1.953E-05 19531.25 390.625 78.125 19.53125 51200
75 0.013333 1.302E-05 13020.83 260.4167 52.08333 13.02083 76800
100 0.01 9.766E-06 9765.625 195.3125 39.0625 9.765625 102400
Table 6 T spike related to fps
The partial spike time refers to the quarter component part of the biphasic pulse
which can be accommodated using the clock pulse (10ns) of a typical FPGA running
at 100MHz. For this chapter, dealing with AER stream production, we could put this
consideration on hold and typify the AER sender chip as operating at circa 25MHz
with an address event timing of T ae = 39062.5 ns and a spike time of 156.25 ns.
For one pixel of an image at maximum intensity there will be fifty `outerpulses’ i.e.
the actual spike plus the time before another one is allowed; or makes sense. As this
pixel information must be transmitted in one second; each outerpulse, in real time,
must take 0.02s. So in conventional terms for a frame rate of 50fps then each pixel,
during propagation, experiences one outerpulse per frame albeit at faster than `real
time’. As biologically the innerpulse (comprising `spike’ plus recovery time) takes
4ms (0.004s) this implies an `off’ time; at maximum intensity of (0.02-0.004) equals
0.016s, again in `real time’, as has been previously stated. Using an example of a
1024 pixel image at 50fps as each frame takes 0.02s then the serialised time for a