Linear Amplifier Facts Worth Noting
One type of electronic circuit that you should know about is a linear amplifier. With this circuit, it has a proportional output and input yet delivers more power straight into a load. This is also the term that is used to refer to a power amplifier that is powered by radio frequency. This is often found in amateur radios, and you can also measure the output power in some of them in kilowatts. These linear amplifiers are also being used in laboratory and audio equipment.
Linearity is the ability of an amplifier to be able to create signals that are exactly the same copies of the input. Such signals can be produced with high power levels. The efficiency of linear amplifiers, though, is affected by certain factors. Load impedance, power output, supply voltage, and input base current capabilities are some of these factors.
When it comes to amplifiers, they come in different classes. You have the so-called Class A amplifiers that can showcase good linearity for both push-pull and single-ended variants. Linearity can only be achieved in Class AB1, AB2, and B amplifiers, though, when a tuned tanked circuit is used. Moreover, for these classes of amplifiers with push-pull topology, there must be two active elements for the positive and negative parts. These elements are transistors and tubes. Lastly, Class C amplifiers are in no way linear.
These different classes of amplifiers can be used in a wide range of purposes. Each of them has something to offer in terms of signal accuracy, efficiency, and implementation cost. They have different uses in radio frequencies.
The most inefficient of these different linear amplifiers are the Class A ones. When it comes to their efficiency rating, it does not go beyond 50%. Throughout the entire radio frequency cycle, the vacuum tube or semiconductor conducts. For a vacuum tube, the mean anode current should be set to the middle linear section of the curve found on the anode current.
Meanwhile, Class B linear amplifiers are 60 to 65% efficient. With the use of a large drive power, conduction in half the cycle can be achieved with their vacuum tube or semiconductor.
Class AB1 has a grid that is more negatively biased compared with Class A linear amplifiers. Class AB2 linear amplifiers, on the other hand, have a more negatively biased grid than that in Class AB1 linear amplifiers. Moreover, the input signal has been shown to be larger. The grid current will also increase more when the drive is able to turn the grid positive.
And yet, if you are looking for the most efficient linear amplifiers, you have the Class C amplifiers. Getting an efficiency of 75% is expected when a 120-degree conduction range is achieved. However, they are really not that linear. This implies then that non-AM modes are their only use with the likes of FM, RTTY, and CW.