From Class Wiki
- 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
|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
| Gain |
- 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,
- 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.