Matching and Gain in RF Circuits

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Matching and Gain in RF Circuits [Copy link]

In RF circuits, matching and gain are two inseparable concepts. Matching refers to adjusting circuit parameters so that signals can be transmitted smoothly between various parts, while gain refers to the ability of the circuit to amplify the input signal to the required output level. In RF circuit design, it is crucial to correctly understand and handle the relationship between matching and gain.

Matching and gain are important design considerations in RF circuits. First we need to understand their definitions.

The concepts of matching and gain and the relationship between them

Matching :

In RF circuits, matching is the key to ensure the maximum power transmission of signals. Matching circuits are used to match the impedance of signal sources, loads, and intermediate circuits with the characteristic impedance of transmission lines or components in the circuit. Matching circuits usually include matching networks, transmission lines, and tuning circuits. Through matching, the reflection loss of signals can be minimized and the performance and efficiency of the circuit can be improved.

Gain :

In RF circuits, gain refers to the ability of the circuit to amplify the input signal. Gain is very important in RF systems because it determines the strength and range of the signal. Common gain components in RF circuits include power amplifiers and low noise amplifiers. Designers need to balance gain and other performance indicators such as noise figure, linearity, and bandwidth to meet system requirements.

Effect of matching on gain:

Good matching can maximize the power transmission efficiency of the RF circuit and reduce the reflection loss of the signal, thus helping to increase the gain of the circuit. When the impedance of the input signal source and the circuit is well matched, the signal can be transmitted to the load or the next cascade circuit to the greatest extent, reducing signal loss, so a higher gain can be obtained.

Theory and Analysis

Circuit Model

This article uses the RF amplifier module as a prototype for analysis

Schematic diagram of RF amplifier model

Conjugate matching concept

The RF energy signal is transmitted from the signal source to the load, and its output characteristics can be explained by the "water management theory".

Conjugate matching: the real resistances are equal and the imaginary reactances cancel out.

Matching Network Design

We mark the relevant reflection coefficient and impedance on the circuit model. The subscript s represents the source end, L represents the load end, IN represents the input end of the amplifier, and OUT represents the output end of the amplifier.

When the characteristic impedance is 50, the relationship between the transient reflection coefficient (considering the device to be a unidirectional device) and the resistance is:

Impedance and Matching

Example

Maximum power gain matching condition (for high gain amplifier)

The reflection coefficient at the matching source is equal to the conjugate of the reflection coefficient at the amplifier input

The conjugate of the reflection coefficient at the output is equal to the reflection coefficient at the output of the amplifier

Best noise matching condition (for low noise amplifier)

Because it is a low noise amplifier, the reflection coefficient at the input of the amplifier must be equal to the reflection coefficient when the noise figure is optimal , so the relationship is as follows:

Maximum output power matching conditions (final power amplifier)

Because we need the maximum output power, the reflection coefficient of our output matching network needs to be when the output power is maximum. OPT: Maximum Pout, not maximum gain, which is related to the nonlinearity of the power transistor (P1dB). The relationship is as follows:

In summary, matching and gain in RF circuits are closely linked and affect each other. Through appropriate matching technology, we can maximize the gain of the circuit and ensure the quality and stability of signal transmission. Therefore, in RF circuit design, we should fully consider the relationship between matching and gain to achieve efficient and reliable circuit performance.

Jacktang

How can we explain the relationship between matching and gain in RF circuits in the most common language, in one sentence?

btty038

Have you ever seen a dime become 100? It's a similar principle.

秦天qintian0303

What factors limit the matching and gain in RF circuits?

赤野猎魂

Okay, good ...

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Qintianqintian0303 posted on 2023-7-25 12:08 What factors limit the matching and gain in RF circuits?

Operating point, frequency, operating bandwidth, materials used, impedance of the selected device,