Learn from the Quiz!

Thursday, 11 July 2019

12:00 AM

  • There is a small resistance when looking into a voltage source
  • You can model a voltage source in series with a resistor between any two terminals in a linear network
  • In finding a Thevenin equivalent circuit, short circuit all independent voltage sources
  • Machine generated alternative text:
    • The Norton current between  and  is
    • The Thevenin resistance between  and  is
    • The Thevenin voltage between  and  is
    • The value of  should be much larger than  for maximum voltage transfer to the load
  • If a certain two port network has  as one of its admittance paramaters,  should be
  • The 3 dB frequency
    • Is where the gain is reduced by approximately 70%
    • Is where power is reduced by half
    • Is where power is reduced by 3 dB
  • For a transfer function which has two poles at 500 & 200000, and two zeros  at 10000 & 15000, the pole at 500
    • Will reduce the magnitude of the gain by 20 dB per decade from 500 onwards
    • Will introduce a phase shift of 45 degrees at 500
    • Will introduce a phase shift of 49 degrees at 5000
  • For a transfer function , the gain magnitude at  is approximately
  • For a transfer function , the bandwidth is
  • With an (ideal) op-amp
    • The inverting and non-inverting inputs are at virtual ground
    • No current flows into the input of the op-amp
    • It is direct coupled
    • Very large open-loop gain
    • Infinite bandwidth
    • Very large input resistance
    • The compensation capacitor provides the op-amp stability by creating a dominant pole
  • Suppose the unity gain frequency of a particular op-amp with an internal compensation capacitor is .
    • When configured as a non-inverting amplifier with a gain of 100, the bandwidth would be
    • When configured as an inverting amplifier with a gain of -100, the bandwidth would be
  • Suppose the unity gain frequency of a particular op-amp with an internal compensation capacitance of  is . The unity gain frequency would change to be larger than  if the compensation capacitor were to be changed to
  • DC imperfections result in
    • Input offset voltage
    • Input offset current
    • Input bias currents
  • Output offset voltage DC imperfections in non-ideal op-amps are caused by a mismatch in input transistors

 

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  • Electrons in the conduction band and valence band are responsible for current conduction in silicon
  • By convention, the direction of current is assumed positive in the direction to which holes flow
  • In intrinsic silicon
    • The concentration of holes and electrons are dependent by temperature
    • The concentration of holes and electrons are equal
    • Hole movement is achieved by valence electrons hopping and filling holes
  • To form n-type silicon, intrinsic silicon can be doped with phosphorus
  • To form p-type silicon, intrinsic silicon can be doped with aluminium
  • In doped silicon, the concentration of free carriers are controlled by the doping concentration
  • In an extrinsic semiconductor, if the doping concentration is
    • The concentration of majority carriers is approximately
    • The concentration of monitory carriers is inversely related to
  • Current flow in semiconductors is achieved by
    • Applying an electric field
    • Concentration gradient in free carriers
  • A n-type doped silicon is more conductive than a p-type doped silicon
  • When an n-type doped silicon and p-type doped silicon is brought together and diffusion is possible across the contact area
    • Holes diffuse from the p-type to the n-type piece
    • Holes recombine with electrons in the n-type piece
    • A depletion region is created across the PN junction with similar widths in each piece
  • The potential barrier created within the depletion region
    • Depends on temperature
    • Depends on the majority carrier concentrations in the p-type and n-type
  • The width of the depletion layer
    • Gets narrower as the majority concentrations increase
    • Gets wider when the PN junction is reverse biased
  • Drift current does not increase when a PN junction is reverse biased
  • Diffusion current reduces when a PN junction is reversed biased
  • A forward biased PN junction results in a higher diffusion current
  • In a forward biased PN junction, the forward current is caused by
    • Holes injected from P to N
    • Electrons injected from N to P
    • Recombination of holes with electrons in the N type
    • Recombination of electrons with holes in the P type
  • The recombination of holes with electrons in the N type piece of a PN junction
    • Contributes to the majority carrier forward current flow
    • Decreases exponentially with distance from the edge of the depletion layer
    • Is equal to the diffusion current of holes in the N type
  • The forward current starts to increase exponentially once the knee voltage (of around 0.5-0.7V) is exceeded
  • Zener diode breakdown occurs before avalanche breakdown
  • The junction may break down if a large reverse voltage is applied
  • For a BJT
    • The base must be thin
    • The Base-Emitter junction must be forward biased
    • The Base-Collector junction must be reverse biased
    • Doping concentration of the emitter is significantly higher than the base and collector
  • BJTs usually operate in forward active mode
  • For a BJT biased in forward active mode, the typical voltage between the base and emitter is around 0.7 V

 

 

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