Today, I Learned

1. EEC

• Two among four topics we are gonna learn this class: Ingerver, Filter

• Convention for writing voltage and current is to use the same direction.
  (However, this is only a convention not a rule)

• General units for calculating circuits: V, mA, kOhm.
  For example, Calculating the current in a circuit with 1.5V and 1kOhm, ignoring the units(10^3 for kilo), we can simply get 1.5mA.

• Power
  Power = work/time = work/charge*charge/time = voltage * current.
  In short, P = VI = I^2R = V^2/R
  If some element's power (V * I) is positive, that elements are comsuming the power.
  Otherwise, if negative, that elements are procucing the power(like batteries).

• Two-terminal circuit element.
  x-axis : voltage. y-axis : current
  Registers that follows the Ohm's law's I-V graph can be drawn on the plane with the slope of 1/R.
  

• Conductance
  - Inverse of resistance.
  unit: mho(℧), Simenses(S)

• ++ Diode **
  - Electronic circuit element.
  Characteristic equation:
  I-V Characteristic grpah:
  

  However, to simplify the graph using two linear graph, we divide this graph.

• Open, Short circiut
  1. If there are disconnection between 2 points, say A and B, we say circuit is opened.
  In this situation, current(i ) goes 0 regardless of voltate(V ).

  2. If there are direct connection bewteen 2 points, we say circuit is shorted.
     In this situation, voltage(v ) goes 0 regardless of current(i )

• Practical voltage source.
  If there's a short in the circuit, we might think that with no resistance in a circuit, current will be infinity (i = V/R). However, that is impossible in a real world since there is small internal resistance of the voltage source.
  When there are another resistance in a circuit, we usually ignore the internal resistance since that is much much smaller than the other resistances, however, without any resistance we have to take it into an account.

• Practical current source.
  Similar to the above situation, if circuit with current source opened, we might think that in this situation resistance equal to infinity which means voltage also be infinity. However, we this is impossible in a real world since there is large register of the current source.

• Circult Graph
  branch : circult element
  node : interconnection of circuit element
  mesh : loop that has no loop inside
  

2. CA

• A computer is a programmable machine.
  In 1945, von Neumann address architecture that has CPU, MEMORY.
  Still, all of computer follows that structure.

• The number of transistor in a chip can be represent the ability of the chip.
  Following the moore's law, the number of transistors in a chip will approximately double every 24 months.
  Wafer -> Die -> Chip

• Levels of program code
  + High-level language

  • Assembly language
    for humans.
    
  • Machine language
    for machines.

• How to or Who fill the gap between software and hardware?
  - ISA (Instruction Set Architecture)

  • Is the hardware/software interface.