Transistor Amplifiers

Study Notes

The current gain of a transistor amplifier is defined as the ratio of output current to input current
It is typically denoted by the symbol β (beta) and is a dimensionless quantity
β is a measure of how much the transistor amplifies the input current
A higher β indicates a higher current gain, which means a smaller input current is required to produce a certain output current
Typical values of β for bipolar junction transistors (BJTs) range from 10 to 500

Power amplification refers to the ability of a transistor amplifier to increase the power of the input signal
The power gain of an amplifier is defined as the ratio of output power to input power
Power amplification is achieved by using a high-power transistor and a suitable load impedance
There are several classes of power amplifiers, including:
- Class A: High power conversion efficiency, but low power output
- Class B: High power output, but low power conversion efficiency
- Class AB: A compromise between Class A and Class B

The frequency response of a transistor amplifier refers to its ability to amplify signals of different frequencies
The frequency response is typically measured by plotting the gain of the amplifier against frequency
There are several factors that affect the frequency response of a transistor amplifier, including:
- The cutoff frequency of the transistor
- The load impedance
- The parasitic capacitances and inductances of the amplifier
The frequency response of an amplifier can be classified into three regions:
- Low-frequency region: The gain is relatively constant
- Mid-frequency region: The gain decreases with increasing frequency
- High-frequency region: The gain is significantly reduced

There are several common amplifier configurations, including:
- Common emitter (CE) configuration: The most common configuration, which provides a high current gain and a moderate voltage gain
- Common collector (CC) configuration: Also known as an emitter follower, which provides a high current gain and a low voltage gain
- Common base (CB) configuration: Provides a high voltage gain and a low current gain
Each configuration has its own advantages and disadvantages, and the choice of configuration depends on the specific application