This was buried in another thread and deserved it's own place.
Amplifier Class Description Conduction Angle
Class-A Full cycle 360o of Conduction θ = 2π
Class-B Half cycle 180o of Conduction θ = π
Class-AB Slightly more than 180o of conduction π < θ < 2π
Class-C Slightly less than 180o of conduction θ < π
Class-D to T ON-OFF non-linear switching θ = 0
Lets get some fundamental myth out of the way .
Solid-state amplifiers cannot be class "AB1" or class "AB2". A bipolar transistor amp cannot be a sub 1 or sub 2 class because they do not have grids to have or not have grid current. Solid-state amplifiers have bases or gates, and a bipolar transistor always has base current.
Class AB does not mean the amplifier is linear. "Linear" in the context of amplifiers indicates a linear transfer function, or a transfer function that has the proper transfer function curve shape to minimize odd-order intermodulation products. A linear transfer function generally means the output power level tracks the input power level in a way that does not cause excessive 3rd, 5th, 7th and other odd-order mixes. Only odd-order mixing or distortion produces annoying splatter.
The bias current can NOT remain steady because the bipolar requires a change in base current to produce a change in collect current.
If the bias current remains steady with varying drive, the amplifier will have gain compression.
If the VOLTAGE supplied to the bias system remains fixed at a level that produces the correct Ic for the device junction temperature, the amplifier will not gain compress when the exciter power rectified in the EB junction tries to add negative voltage back into the bias supply.
If the current is regulated, the bias will go negative as drive is increased.
That's why high power transistors can not be correctly biased without an active bias system that maintains constant voltage with a very low bias dynamic source impedance .
FET's, because they have no gate current (hopefully), require only
a regulated voltage source of almost any impedance.
I have more to include in following posts.
I'd like to thank Tom Rauch and https://www.electronics-tutorials.ws/amplifier/amplifier-classes.html for the text and graphics
Sławomir Kleczyk for the photos.
Amplifier Class Description Conduction Angle
Class-A Full cycle 360o of Conduction θ = 2π
Class-B Half cycle 180o of Conduction θ = π
Class-AB Slightly more than 180o of conduction π < θ < 2π
Class-C Slightly less than 180o of conduction θ < π
Class-D to T ON-OFF non-linear switching θ = 0
Lets get some fundamental myth out of the way .
Solid-state amplifiers cannot be class "AB1" or class "AB2". A bipolar transistor amp cannot be a sub 1 or sub 2 class because they do not have grids to have or not have grid current. Solid-state amplifiers have bases or gates, and a bipolar transistor always has base current.
Class AB does not mean the amplifier is linear. "Linear" in the context of amplifiers indicates a linear transfer function, or a transfer function that has the proper transfer function curve shape to minimize odd-order intermodulation products. A linear transfer function generally means the output power level tracks the input power level in a way that does not cause excessive 3rd, 5th, 7th and other odd-order mixes. Only odd-order mixing or distortion produces annoying splatter.
The bias current can NOT remain steady because the bipolar requires a change in base current to produce a change in collect current.
If the bias current remains steady with varying drive, the amplifier will have gain compression.
If the VOLTAGE supplied to the bias system remains fixed at a level that produces the correct Ic for the device junction temperature, the amplifier will not gain compress when the exciter power rectified in the EB junction tries to add negative voltage back into the bias supply.
If the current is regulated, the bias will go negative as drive is increased.
That's why high power transistors can not be correctly biased without an active bias system that maintains constant voltage with a very low bias dynamic source impedance .
FET's, because they have no gate current (hopefully), require only
a regulated voltage source of almost any impedance.
I have more to include in following posts.
I'd like to thank Tom Rauch and https://www.electronics-tutorials.ws/amplifier/amplifier-classes.html for the text and graphics
Sławomir Kleczyk for the photos.
