Amplifier Circuit Design

Study Notes

Voltage Amplifiers: Amplify a weak input voltage signal to a higher voltage level
Current Amplifiers: Amplify a weak input current signal to a higher current level
Power Amplifiers: Amplify a weak input signal to a higher power level (both voltage and current)

Common Emitter (CE) Amplifier: A basic amplifier circuit with a single transistor, providing voltage amplification
Common Collector (CC) Amplifier: A circuit with a single transistor, providing current amplification
Differential Amplifier: A circuit with two transistors, providing high common-mode rejection and amplification of differential input signals

Gain: The amount of amplification required, determined by the ratio of output to input signal
Impedance Matching: Ensuring the input and output impedance of the amplifier are matched to maximize power transfer
Bandwidth: The range of frequencies the amplifier can amplify, determined by the cutoff frequencies
Noise and Distortion: Minimizing unwanted signals and signal degradation
Stability: Ensuring the amplifier does not oscillate or become unstable

Feedback: Using a portion of the output signal to improve gain, stability, and bandwidth
Biasing: Setting the quiescent operating point of the transistor to ensure proper amplification
Impedance Transformation: Using transformers or other components to match impedances
Active Loads: Using active devices (e.g., transistors) to replace passive loads (e.g., resistors) for improved performance

Common Emitter (CE) amplifier: a basic amplifier circuit with a single transistor, providing voltage amplification
Common Collector (CC) amplifier: a circuit with a single transistor, providing current amplification
Differential amplifier: a circuit with two transistors, amplifying differential input signals while rejecting common-mode signals

Feedback improves gain, stability, and bandwidth by using a portion of the output signal
Biasing sets the quiescent operating point of the transistor for proper amplification
Impedance transformation uses components like transformers to match impedances
Active loads replace passive loads with active devices (e.g., transistors) for improved performance

Voltage amplifiers amplify input voltage while keeping output current constant.
Current amplifiers amplify input current while keeping output voltage constant.
Power amplifiers amplify both input voltage and current to increase output power.

Common Emitter (CE) configuration is the most widely used, providing both voltage and current gain.
Common Collector (CC) configuration provides current gain but no voltage gain, ideal for impedance matching.
Common Base (CB) configuration provides voltage gain but no current gain, suitable for high-frequency applications.

Gain is the ratio of output signal to input signal, measured in decibels (dB).
Bandwidth is the range of frequencies over which the amplifier provides a constant gain.
Sensitivity is the minimum input signal required to produce a specified output signal.
Linearity is the ability of the amplifier to produce an output signal directly proportional to the input signal.

Audio amplifiers are used in speakers, headphones, and music systems.
Radio Frequency (RF) amplifiers are used in wireless communication systems such as radios, mobile phones, and satellite communication.
Instrumentation amplifiers are used in medical equipment, industrial control systems, and scientific instruments.

Noise refers to unwanted signals that can reduce amplifier gain and bandwidth.
Distortion is the alteration of the output signal waveform, resulting in a non-linear output.
Slew rate is the maximum rate of change of the output voltage, limiting the amplifier's ability to respond to high-frequency signals.