# Chapter 1

From Class Wiki

## Contents

## Amplifier Models

- These are purely models, and cannot be replicated in a real world environment. They are meant to explain.
- Trans stands for transfer (from voltage to current or visa versa).
- The inputs and outputs can be either current or voltage. This leads to 4 amplifier models.
- You can use any of these models, though some may be easier to work with (if you are given the Thevenin or Norton equivalent).

Amplifier type Gain parameter Gain equation |
Voltage input | Current input |
---|---|---|

Voltage output | Voltage Open-circuit voltage gain |
Transresistance Open-circuit transresistance gain |

Current output | Transconductance Short-circuit transconductance gain |
Current Short-circuit current gain |

Amplifier Type |
Input Impedance |
Output Impedance |
Gain Parameter |
---|---|---|---|

Voltage | 0 | ||

Current | 0 | ||

Transconductance | |||

Transresistance | 0 | 0 |

## Differential Amplifiers

- Differential amplifiers take two (or more) input sources and produce an output voltage proportional to the difference between the input voltages.
- Instead of expressing the input voltages in terms of and , we can express them in terms of the differential and common-mode input.
- Differential input signal is the difference between the input voltages.
- Common-mode input signal is the average of the input voltages.
- , if is voltage at the positive terminal.
- , if is voltage at the negative terminal.

- , where is the differential gain and is the common mode gain.
- The common-mode rejection ratio (CMRR) is the ratio of the magnitude of the differential gain to the magnitude of the common-mode gain.
- In decibels,

## Definitions

- Input Resistance: of an amplifier is the equivalent resistance seen when looking into the input terminals.
- Output Resistance: is the Thevenin resistance seen when looking back into the output terminals of an amplifier.
- Open-circuit voltage gain: the ratio of output amplitude to input amplitude with the output terminals open circuited.
- Short-circuit current gain: the current gain with the output terminals of the amplifier short circuited.