w6 Flashcards
A neurostimulator delivers 250 uA of current for 25
us. How much charge is delivered?
(250 uA) * (25 us) = 6.25 nC
do implantable neurostimulators use voltage sources or current sources
use current sources to provide a constant (and defined) current
capacitors resist a change in _____
inductors resist a change in _____
voltage
current
Transistors can be used as a switch or amplifier, in analog or digital circuits.
what is the most commonly used type of transistor
Most commonly used type are CMOS (Complementary
Metal Oxide Semiconductor)
easy to make
what is the basic operation of mosfets
Voltage difference between the gate and the source controls the current between the drain and the source
No current flows into the gate (hence they are very low power devices)
what are Digital Logic circuits
Utilise Boolean logic (1/0, True/False, On/Off)
Made of transistors. They’re analog circuits. Memory elements are used to store a digital value. Traditionally these have been flip flops or latches (set reset latch). Built using combinations of digital logic gates (in effect, many transistors)
describe the output of a NAND logic gate
Input: 0, 0 Output: 1
Input: 0, 1 Output: 1
Input: 1, 0 Output: 1
Input: 1, 1 Output: 0
1 if not and, opposite value if and
describe the relationship between logic 0 and logic 1 with voltage in Digital Logic circuits
Logic 0 = a low voltage, Vss , close to circuit ground
Logic 1 = a high voltage Vdd , close power supply
positive gate voltages => input (nmos) transistors are on, inner (pmos) transistors are off => current flows between input transistors only => current doesn’t flow to output / flows to ground
what is Sequential logic
A sequence of memory elements and digital logic gates. These are the core of many electronic systems.
Memory elements are used to control the data flow through the system.
A master signal (clock) is used to sequence the processing of events.
what are the requirements for neurostimulators
High reliability, up to 70+ years for some implantable devices.
Safe for the recipient and clinician, such as: Preventing DC currents, Safety mechanisms to prevent overstimulation, Not exceeding specified current levels for the recipient.
what are some circuit blocks that occur in neurostimulators
Transmitter and receiver (to communicate with external
components).
Control circuitry (e.g. microprocessor, digital control logic).
Current stimulus drivers to deliver current to the electrodes.
Circuitry to record stimulus and nerve responses (neural response).
Power supply management circuits.
what does upstream and downstream mean (in terms of circuits)
Upstream - internal to external
Downstream - external to internal
what is telemetry
the collection of measurements or other data at remote or inaccessible points and their automatic transmission to receiving equipment for monitoring.
upstream process
how is control circuitry usually designed
usually implemented using standard low voltage transistors in well defined design flows (e.g. digital synthesis)
what does a current stimulus driver do
Bias current generated in the power management circuit is then scaled and output to electrodes.
Current mirrors are often used for this
