Pulse Generator and Their Applications

B/8 pulse generators and their applications. Electrical pulses used in both diagnostic and threpatic. used for the stimulation of damaged skeletal muscles in order to restore lost function. for example defibrillator is used to stop the deadly condition of ventricular fibrillation. in which the heart beats very fast but too superficially for sufficient pumping. introduction two state digital systems are used have a resting state and activated state. they typically produce pulses in the square shape. only one state is allowed (permitted) between activated and resting there is forbidden state. -> permitted states -> stable, non-stable. transition between 2 states is always evoked by a signal which is a pulse that exceeds the threshold level. this signal is called trigger pulse. pulse generators 1- monostable -> 1 stable state 2- Astable -> 0 stable state multivibrator. 3- bistable -> 2 stable state. (1) monostable multi vibrator (defibrillator) also called one-shot or monoshot by an input pulse. it give a single output pulse of determined duration. Operation -> a rising edge of the square pulse is created by a trigger pulse, but the system returns spontaneously without further triggering to its stable state. -> after the time given by the time delay. R, C the resistance of chest -> R the capacitor of capacitance C is discharged. U_R = U₀ * e^(-t / RC) (exponential function) exponentially decreasing electric current flows through the resistance R. -> also there is voltage decrease exponentially. time constant (τ) -> the time that voltage on the timing capacitor decreases to U₀/e value. τ = RC the time constant of the pulse can be set by the R and C elements of the circuit. RC-circuit used for the timing of a MMV. Values of R, C -> determines the τ [A diagram shows an exponential decay curve of voltage U_R over time t, starting from U₀ and decreasing. A square pulse is shown underneath, triggered at the start, with its width corresponding to the time constant. Annotations include "smaller slope," "higher slope," "trigger," and "dropping edge."] time delay -> is the time that system stays in the activated state. in monostable multivibrator the system stays in the resting state, until another trigger pulse arrives. Defibrillator -> the electrodes placed on the chest of the patient, which deliver the electric pulse (charge) of the charged capacitor to the heart upon pressing the start button of the device (trigger). [Two graphs are shown. The top graph (U_in vs t) shows a single sharp trigger pulse crossing a threshold line. The bottom graph (U_out vs t) shows a single square wave pulse with a "rising edge" and a "dropping edge," and a width labeled "T time delay."] (2) Astable multivibrator (Pace maker) by connecting two MMV in a ring. we get a AMV -> also called free-running multivibrator or relaxation oscillator. Operation -> The output of the first MMV (dropping edge) triggers the second MMV, which subsequently triggers the first MMV and this process continues on and on... this way we get a periodic square pulse generator. any of the connected in and the out puts can be used as the AMV output. [Two graphs (U_out1 vs time and U_out2 vs time) show continuous, periodic square wave pulses, where the falling edge of one pulse train appears to trigger the rising edge of the other.]