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4066 Bilateral Switch questions

Discussion in 'Electronic Basics' started by Pete, Jul 18, 2003.

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  1. Pete

    Pete Guest

    Hi group,

    I am a genuine newbie to electronics trying to understand the operation of
    an 4066 IC bilateral switch. It has 4 switches, only two of which I need to
    use. For each switch, there is three connections - ctrl, I/O and O/I. Here's
    my questions:

    1. what do these connections actually mean?
    2. why do you need 3 connections to make a switch - I though 2 was
    sufficient?
    3. the first switch also has two other connectors labelled vDD and vSS -
    what do these mean?

    This is all gobbledegook to me so all assistance is greatly appreciated.
     
  2. Ctrl is the control line that turns each switch on or off. If the
    control line has the same voltage as the Vss pin, the switch is off.
    If it has the same voltage as the Vdd pin (ordinarily 3 to 18 volts
    more positive than Vss) the switch is on.

    I/O and O/I mean that either of these can be signal in and either can
    be signal out. The voltage on both should be anywhere between Vss and
    Vdd at all times.
    Those are the power pins for the inverter logic inside the chip. When
    you take a ctrl pin high, the inverse (low) is also needed,
    internally, and vice versa. These switches are made up of N and P
    channel mosfets, and it takes a positive voltage to turn an N channel
    mosfet on, and a negative voltage to turn a P channel mosfet on.
    Since these switches are made to conduct in either direction, they are
    made up of a P channel and an N channel mosfet connected in inverse
    parallel. The data sheet covers this pretty well.

    http://www.fairchildsemi.com/ds/CD/CD4066BC.pdf
     
  3. (snip)

    Be sure to tie the unused ctrl lines to either Vss or Vdd, to keep
    them from floating around and causing high current consumption by the
    internal inverters.
     
  4. A switch path has two terminals, any one of which can be either an input
    or output, hence I/O, O/I
    How do you propose to turn the switch on and off without a voltage
    control input?
    VDD - most positive supply voltage
    VSS - most negitive supply voltage


    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
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