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Analogue Switch




Unlike a relay, however, the analogue switch does not provide electrical isolation between the analogue signal and the control signal. This means that it should not be used in high-voltage circuits where such isolation is desired. Also, since there is only a low current path between the input and output, the maximum Current allowed to flow through the switch may be smaller than that in a typical relay. There are also some constraints on the polarity and range of voltages of the signal being switched.

Important parameters of an analogue switch are:
  • on-resistance: the resistance of the MOSFET when switched on. This commonly ranges from 5 Ohms to a few hundred ohms.

  • off-resistance: the resistance of the MOSFET when switched off. This is typically a number of megaohms or gigaohms.

  • signal range: the minimum and maximum voltages allowed for the signal to be passed through. If these are exceeded, the switch may be destroyed by excessive currents. Older types of switch can even '' Latch Up '', which means that they continue to conduct excessive currents even after the faulty signal is removed.

  • charge injection. This effect causes the switch to inject a small Electrical Charge into the signal when it switches on, causing a small Spike or Glitch . The charge injection is specified in Coulomb s.