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I need a signal that most of the time will work as a power supply for the microcontroller but at some external event a positive pulse will be generated and added to the normal power supply. Power supply is set once and it never changes, however the pulse will be different.

My question is: I have a powerful glitch generator that can provide only a voltage pulse so I need to add a stable power supply. What is the best way of doing it? I want to keep the parameters of the glitch as close as possible to the device characteristics (rising and falling edges are around 200 ps), hence the schematic does not have to introduce a big distortion to it. Could you give me some tips or descriptions for doing it.

I am not an electrician, I am mathematician doing research in software and I need to disturb this software during the microcontroller run by this exotic way.

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  • \$\begingroup\$ What, precisely, do you want the controller to do? Can you include a rough schematic of what you need? 100ps is really a bit too fast for a uC to handle \$\endgroup\$ – Chintalagiri Shashank Mar 1 '13 at 3:00
  • \$\begingroup\$ Poorly specified, but it sounds like the goal is to cause "interesting" mis-operation, either to study reliability or to try to bypass security features. \$\endgroup\$ – Chris Stratton Mar 16 '13 at 23:26
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If your glitch generator doesn't have to be ground referenced then it can be added in series with the output of a power supply. However, the glitch generator needs to have an internal circuit path to allow the power supply dc current unimpeded. If it does need to be ground referenced then the Power supply might be designed so that it doesn't need to be ground referenced i.e. an isolating DC-DC convertor would do this.

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You power supply (if it was any good) should have very low output impedance, meaning it will present low resistance path for your glitch generator.

You should put a forward biased diode in a series with your power supply (anode to the PS positive terminal, cathode to your circuit), and then behind the diode (at the cathode) you can connect your supply glitch generator. Schottky diodes should ideally be used, even smaller ones would handle short current bursts without problems.

The steady state voltage of your glitch generator should be same as the power supply nominal voltage, and the diode will prevent the current to flow back into your power supply when the 'glitch' was turned on. You can also add a diode in series with your glitch generator output to prevent power supply feeding it back when the PS output is higher. In this case you don't really care about the glitch voltage in a steady state, supply will be defined by the main PS until you 'fire' the glitch above the PS nominal level.

Basically you just create the power supply voltage 'OR' function in a sense that your uC will 'see' higher of the two voltages, same as when you provide power supply backup for some circuit.

Take care not to destroy your microcontroller, very easy thing to do also with under voltages due to the power supply lead inductance when high rise time pulses with significant current are applied like that.

Industrial equipment for such tests have 'glitch' characteristics based on some standards for rise time / fall time / energy etc.

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protected by W5VO Feb 19 '13 at 21:54

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