Fig 1.
A. Standard stimulation pulse train with active charge balancing. The amplitude of the stimulation pulse Qs can either be a voltage or current pulse depending on the stimulation method. The variable ts is the duration of the pulse, common values are 60 μs or 90 μs. td is the inter-pulse interval, the amount of time between the stimulation pulse and the charge balanced pulse. Qc is the amplitude of the active charge balanced pulse and tc is the period, this pulse can either be symmetric or asymmetric. Finally, tp is the period between pulses, this parameter is the inverse of the pulse frequency. B. An example of a non-constant pulse train, in this case a delayed feedback scheme. C. Gaussian stimulation waveform. D. Sine-wave stimulation waveform. E. Triangular stimulation waveform.
Fig 2.
Schematic circuit diagram of the brain stimulation device.
Fig 3.
A. A picture of the developed DBS device whose dimensions are 32.5 × 28 × 8 mm. B. The device being weighed with the battery installed. C. The device being weighed with the battery removed.
Fig 4.
Sample outputs of the DBS device across a 3 kΩ resistive load demonstrating the flexibility of the output.
A. A typical symmetric DBS pulse with active charge balancing, 130 Hz, 90 μs, 200 μA stimulation and 90 μs, -200 μA charge balancing. B. An asymmetric charge balanced pulse with an inter-pulse delay, 130 Hz, 90 μs, 200 μA stimulation and 360 μs, -50 μA charge balancing with a 90 μs inter-pulse delay. D. A Gaussian stimulation pulse with 200 μA amplitude at 130 Hz with a 50 μs inter-pulse delay. E. A sinewave stimulation pulse with 200 μA amplitude at 130 Hz with a 50 μs inter-pulse delay. F. A triangular stimulation pulse with 200 μA amplitude at 130 Hz with a 50 μs inter-pulse delay. G. A continuous sinewave with amplitude 200 μA and frequency 10 kHz. H. A typical stimulation pulse-train using the stimulation pulse from Fig 4C. I. A pulsatile delayed feedback stimulation example using the pulse shape in Fig 4C.
Fig 5.
The results of the output regulation experiment.
The results clearly show that the circuit successfully outputted both current amplitudes (200 and -200 μA) with regulation of 99%.
Fig 6.
Oscilloscope captures of the return current across a 10 nF capacitor at the shorting phase of a biphasic stimulation pulse.
The measured τ of the 200 μA pulse was 131.7 μs and the 100 μA pulse was 155.7 μs. A. The input waveform for the 200 μA pulse test. B. The input waveform for the 100 μA pulse test. C. The voltage across the capacitor in the 200 μA pulse test. D. The voltage across the capacitor in the 100 μA pulse test. E. The voltage across the capacitor in the 200 μA pulse test shown on a smaller scale so the charge balancing can be observed. F. The voltage across the capacitor in the 100 μA pulse test shown on a smaller scale so the charge balancing can be observed.
Fig 7.
The experimental setup for the saline in-vitro test.
Table 1.
A comparison of DBS systems found in both the preclinical and clinical context.