The NOT gate


Posted on Feb 7, 2014

The single-transistor inverter circuit illustrated earlier is actually too crude to be of practical use as a gate. Real inverter circuits contain more than one transistor to maximize voltage gain (so as to ensure that the final output transistor is either in full cutoff or full saturation), and other components designed to reduce the chance of acc


The NOT gate
Click here to download the full size of the above Circuit.

idental damage. This circuit is composed exclusively of resistors and bipolar transistors. Bear in mind that other circuit designs are capable of performing the NOT gate function, including designs substituting field-effect transistors for bipolar (discussed later in this chapter). Let`s analyze this circuit for the condition where the input is "high, " or in a binary "1" state. We can simulate this by showing the input terminal connected to Vcc through a switch: In this case, diode D1 will be reverse-biased, and therefore not conduct any current. In fact, the only purpose for having D1 in the circuit is to prevent transistor damage in the case of a negative voltage being impressed on the input (a voltage that is negative, rather than positive, with respect to ground). With no voltage between the base and emitter of transistor Q1, we would expect no current through it, either. However, as strange as it may seem, transistor Q1 is not being used as is customary for a transistor. In reality, Q1 is being used in this circuit as nothing more than a back-to-back pair of diodes. The following schematic shows the real function of Q1: The purpose of these diodes is to "steer" current to or away from the base of transistor Q2, depending on the logic level of the input. Exactly how these two diodes are able to "steer" current isn`t exactly obvious at first inspection, so a short example may be necessary for understanding. Suppose we...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Oscilloscope-preamplifier
    Phone-recorder
    5W 7Mhz Rf Power Amplifier Circuit
    switches Default-on latch-off MOSFET power switch
    ESR-Meter
    dc servo motor controller
    Summing amplifier/ Inverting adder circuit using op amp 741
    Features and Power Control Circuit
    Acoustic Sensor
    Coop automatically fill light circuit
    Vibration burglar alarm circuit
    Full bridge current driven vertical deflection amplifier circuit diagram TDA4866



    Top