# Key Facts from Reading Chapter 1

The following facts are not profound and are possibly very obvious. Nonetheless, they might help cement certain concepts. Please add things you think would be helpful.

## Transistors

MOSFET diagram <ref> University of Cambridge </ref>
• Conduction in n-type material is from free electrons.
• Conduction in p-type material is from holes (positive particles).
• The function of metal-oxide-semiconductor field-effect transistors (MOSFETs) depends on the voltage applied to the gate.
• Certain ranges of voltage allow no current to flow between the drain and the source. In this way, the MOSFET acts like an open switch.
• Another particular range of voltage allows current to easily flow from the source to the drain.
• When the voltage is in between the ranges of open and closed switch, the MOSFET can smoothly control the amount of current flowing.
• Bipolar Junction Transistors (BJTs) can act as either switches or current controls as well.

## Amplifiers

• An inverting amplifier has a negative voltage gain, $\ {A_{v}}$.
• A noninverting amplifier has a positive voltage gain, $\ {A_{v}}$. (If you get this, you deserve a cookie)
• The power gain,$\ G$, is the ration of the output power to the input power
• $G=\frac{P_{o}}{P_{i}}=\frac{V_o{I_o}}{V_i{I_i}}=A_v{A_{i}}=(A_v)^2\frac{R_{i}}{R_{L}}$
• $\ R_i$ is the amplifier's input resistance and $\ R_o$ is the amplifier's output resistance.

## Decibel Conversion

• Power gain, $\ G$, can be converted to decibels:

$G=(A_v)^2\frac{R_{i}}{R_{L}}$

$\ G_{db}=10 log{A_{v}}^2+10 log R_i - 10 log R_L$

$\ G_{db}=10 log |A_v|+10 log R_i - 10 log R_L$

• By the equation above, we can say voltage gain in decibels can be found with this equation: $\ A_{v dB}=20 log |A_v|$, where $\ A_v$ is the voltage gain and $\ A_{v dB}$ is the voltage gain is decibels.
• Similarly, we can say current gain in decibels can be found with this equation: $\ A_{i dB}=20 log |A_i|$, where $\ A_i$ is the current gain and $\ A_{i dB}$ is the current gain in decibels.

## Differential Amplifiers

• Differential Amplifiers have two inputs. The terminal marked with a "+" is the noninverting input, and the terminal marked with a "-" is the inverting input.
• The differential input signal is given by $\ v_{id}=v_{i1}-v_{i2}$
• The output of an ideal differential amplifier is given by $\ v_o=A_d v_{id}$.
• The common-mode input signal is given by the following: $v_{icm}=\frac{1}{2}(v_{i1}+v_{i2})$.
• A real differential amplifier's output is given by $\ v_o=A_d v_{id}+A_{cm} v_{icm}$, where $\ A_{cm}$ is the common-mode signal gain.

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