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  • mbenkerumass 6:00 am on February 1, 2020 Permalink | Reply
    Tags: Diodes   

    The Schottky Diode 

    The Schottky diode, unlike the PN-junction diode is not made of a n-type and n-type semiconductor junction. Instead, is consists of a highly conductive silicide material or metal compound with an n-type semiconductor silicon material. Different metal compounds will allow for varying forward voltage drops, generally between 0.3 and 0.5 volts.

    schottky1

    IV curves are often referred to when understanding the function of a diode. One difference that can be inferred from the IV curve comparison is that the Schottky forward current can be much larger, making it useful in applications with higher levels of current.

    schottkyiv

     

  • mbenkerumass 6:00 am on January 29, 2020 Permalink | Reply
    Tags: , Diodes   

    Diode Voltage Clipping Circuits 

    We’re already discussed the PN junction in a previous post. Let’s explore some of the applications of the PN diode.

    diode2

    It was already discussed that due to the nature of the PN junction, current is only allowed to flow in one direction. This results in two possible scenarios using a diode, depending on the direction it is facing with respect to the source.

    diode1

    Diode Clipping Circuits

    Diodes in a forward bias allow current to pass, but thereby reducing the voltage level. In a reverse bias, current is stopped but the voltage remains unaffected.

    Diode clipping can be done for either the positive or the negative voltage of a sinusoidal (or analog) input voltage. In order to clip both the positive and negative sides of the input voltage, two diodes are needed.

    Positive voltage clipping:

    d1

    Negative voltage clipping:

    d2

    Two Diodes:

    d3

    If 0.7 Volts is not the desired output clipping voltage, a bias voltage can be added in each situation above.

    d4d5

     

  • mbenkerumass 6:00 am on January 4, 2020 Permalink | Reply
    Tags: Diodes,   

    The P-N Junction 

    A P-N junction is created in a single semiconductor crystal by doping one side as a p-type and one as an n-type. The region where the two types converge is known as the p-n junction.

    The extra electrons that were added to the n-type semiconductor move towards the p-type junction side while the holes added through p-type doping are positioned closer to the n-type junction.

    pnj2

    As electrons leave the n-type region, it becomes positively charged. This process is called diffusion. The depletion region is the area between the p and n-type sides. The state of equilibrium in the p-n junction is the state of the depletion region without any external electrical potential applied. As mentioned before in a previous paper, the Fermi level is the average between the conduction band and the valence band. By altering the levels of electron holes and electrons in the p-type and n-type sections, holes drift toward the the n-type side and electrons move towards the p-type side, which causes both sections to be closer to the Fermi level in their regions of the material.

    pnj

    When voltage is applied to the pn junction, electrons and electron holes from either side tend towards equilibrium. If the positive potential is applied to the p-type and it is more positive than the n-type area, holes will travel towards the negative voltage. Through diffusion, electrons or electron holes may jump through the depletion layer. For the reason however that electron holes (positive charge) may only move in the direction of the n-type region and electrons (negative charge) may only move in the opposite direction. The direction of electron flow, due to their negative charge is opposite the conventional direction of current flow. Since electrons are only moving from the n-type region to the p-type region, it can be understood that current will only move in the direction going from the side of the p-type region towards the n-type region.pnj1

     

     

  • mbenkerumass 10:09 am on November 28, 2019 Permalink | Reply
    Tags: Diodes,   

    Negative Resistance 

    RF/Photonics Lab
    November 2019
    Jared Alves

    Negative Resistance

    Arguably the most fundamental equation in electrical engineering is Ohm’s Law (V = I*R) which states that voltage is proportional to the product of current and resistance. From this equation, it is apparent that increasing a voltage across an element will increase the current through that element assuming the resistance is fixed. With a resistor, electrical energy is dissipated in the form of thermal energy (heat) due to the voltage drop between the terminals of the device. This is in direct contrast to the concept of negative resistance, which causes electrical power to be produced instead of dissipated.

    Generally, negative resistance refers to negative differential resistance, as negative static resistance is not typically used.  Static resistance is the standard V/I ratio while differential resistance takes the derivative dV/dI. The following image shows an I-V curve with several slopes. The inverse of B yields a static resistance, and the inverse of line C is differential resistance (both evaluated at the point A). If the differential curve has a negative slope, this indicates negative differential resistance.

    negres1

    Even when differential resistance is negative, static resistance remains positive. This is because only the AC component of the current flows in the reverse direction. A device would consume DC power but dissipate AC power. This is because the current decreases as the voltage increases, leading to

    negres2

    A tunnel diode is a semiconductor device that exhibits negative resistance due to a quantum mechanical effect called “tunneling”.

     

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