PMOS pull up network?

Discussion in 'General Electronics Chat' started by krnx2oh7, Nov 9, 2012.

  1. krnx2oh7

    Thread Starter New Member

    Jul 17, 2011
    I am having trouble understanding what is called a PMOS pull-up network

    vin is ate the gate
    the source is at the top connected to power
    vd is output, vout
    and a resistor goes from drain to ground below the vout

    When you turn it "off" you put in vg>vth or "high"
    Doesn't it not get pulled up? It goes to 0 because of the conenction to ground.

    I thought pull ups and down refer to the time when no current is flowing. So w/ high gate voltage it is "off" and it is not being pulled up
  2. JDT

    Well-Known Member

    Feb 12, 2009
    Sounds like you have the PMOS pulling the output up (when the PMOS is on), and a resistor pulling to ground (when the PMOS is off). The PMOS is switched on by connecting the gate to ground and switched off by connecting the gate to V+.

    Note that in a PMOS the source is more positive than the drain. It switches on when the gate is more negative than the source. and more negative than the threshold voltage. The opposite polarity to NMOS.