Let’s talk about what the amplifier amplifies
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Let’s talk about what the amplifier amplifies

Posted Date: 2024-02-04

Does the amplifier amplify current or voltage?

Amplifiers can amplify current, voltage, or power, depending on their design and application. Generally speaking, amplifiers are mainly used to amplify voltage or current signals.

Voltage Amplifier is the most common type of amplifier. It receives an input voltage signal and then outputs a voltage signal of the same shape, but amplified by a certain factor. In a voltage amplifier, the voltage of the input signal increases while the current remains essentially the same.

Current Amplifier is another type of amplifier that receives an input current signal and outputs a current signal of the same shape, but amplified by a certain factor. In a current amplifier, the current of the input signal increases while the voltage remains essentially the same.

In addition, there is an amplifier called a power amplifier (Power Amplifier) ​​that can amplify the power of the input signal. Power amplifiers are usually used to drive loads, such as speakers or transmitting antennas, and their purpose is to provide enough power so that the output device can work properly.

How amplifiers amplify signals

Amplifiers amplify an input signal by controlling an increase in the output signal using an excitation signal, such as a voltage or current.

In a simple amplifier circuit, it usually consists of an active component (such as a transistor or op amp) and its associated external circuitry. Below is a schematic diagram of a typical transistor amplifier used to amplify a voltage signal:

When the input signal Vin enters the amplifier, it passes through resistor R1 in the circuit, properly biasing the transistor (providing the proper operating point) and controlling the drain current of the transistor. Based on the conductive properties of the transistor, the output signal Vout is amplified and sent out through the load resistor RL.

The specific process of amplifying the signal is as follows:

1. The input signal Vin acts on the base, causing the base current to change.

2. Changes in base current cause changes in current flow in the transistor.

3. Depending on the transistor type (NPN or PNP), current flows from drain to emitter or from emitter to drain.

4. As the current increases or decreases, the output signal Vout is amplified accordingly.

5. The amplified output signal can be supplied to the load resistor RL, so that it can obtain an amplified high voltage or current signal.

Generally speaking, amplifiers amplify signals by controlling the working status of active components and processing input signals. It uses the properties of a moving element to increase the amplitude of the input signal and produces an output signal that is similar in shape to the input signal but amplified.

amplifier input resistance and output resistance

The input resistance and output resistance of an amplifier are two important parameters that describe the resistance characteristics of the amplifier to the input signal and output load.

1. Input Impedance: Input resistance refers to the resistance provided by the input end of the amplifier to the external signal source. Generally, the higher the input resistance, the smaller the load the amplifier places on the external signal source, and the output current of the input signal source is reduced, thereby reducing the impact on the signal source. Input resistance can be measured with an ohmmeter or other test equipment. A common input resistance is represented by "Rin".

2. Output Impedance: Output resistance refers to the internal resistance at the output end of the amplifier. It describes the resistive characteristics of the amplifier to the load. An amplifier with low output impedance can provide greater output current to better drive the load and reduce signal loss and distortion. A common output resistor is represented as "Rout".

Different types of amplifiers will have different input resistance and output resistance values. Generally speaking, the input resistance of the amplifier should be higher than the output resistance of the signal source to avoid the loading effect of the signal source; and the output resistance should be lower than the input resistance of the load to ensure that the output signal can be effectively transmitted to the load. .

The exact values ​​of the input and output resistors also depend on the amplifier design and application. Some amplifier designs take special measures to improve the performance of the input and output resistors, such as using techniques such as current feedback, negative feedback, or output buffers to improve the resistor characteristics.

The physical meaning of amplifier input and output resistance

The input and output resistance of the amplifier has the following physical meaning:

1. The physical meaning of input resistance: The input resistance represents the resistance between the input terminal of the amplifier and the external signal source. It is actually the ratio between the voltage at the input of the amplifier and the current at the input. The function of the input resistor is to minimize the load effect on the external signal source, so that the output current of the input signal source is reduced, thereby reducing the distortion of the signal source voltage. Amplifiers with high input resistance can reduce the impact on the signal source, so that the signal source output capability is not affected by the load effect on the amplifier input.

2. The physical meaning of output resistance: The output resistance represents the resistance of the internal circuit at the output end of the amplifier to the load. It is actually the ratio between the voltage at the output of the amplifier and the current at the output. The function of the output resistance is to describe the current capability that the amplifier can provide when driving the load. Lower output resistance means the amplifier can deliver greater output current, which drives the load better and reduces signal loss and distortion. Amplifiers with low output resistance can effectively transmit signals to the load, ensuring the accuracy and stability of the output signal.

Input resistance and output resistance have important physical significance in amplifiers. They are crucial for the matching and adaptation between the amplifier, the signal source, and the load, and can affect the stability, linearity, frequency response, etc. of the amplifier performance. Therefore, in amplifier design and application, it is very important to reasonably select and optimize input and output resistors.

Review Editor: Huang Fei


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