There are many RF protocols you can use for wireless communication, and the IC industry has gone to great pains to produce transceiver ICs for common protocols. Depending on the product you want to develop, a compact SoC, module, or transceiver IC for your particular needs. Only the most popular protocols get to see this level of integration, but not all products will benefit from an integrated transceiver or module.

For wireless communication, an RF amplifier is an integral part of the RF front end and signal chain in your product. If you’re just starting out as an RF engineer and you need to select an amplifier, take a look at our RF amplifier selection guide. We’ll run through the important specifications you should pay attention to, how they affect your system, and what options you can expect to find on the market.

RF Amplifiers in Your RF Front End and Back End

There are many components that appear in an RF front end; this generally refers to all the circuitry that appears between the receiver/transmitter antenna and the digital processor. The RF front end in a wireless product can appear as a set of discrete components, a set of ICs, a highly integrated module/SoC, or anything in between. RF amplifiers appear in the Rx and Tx sides of an RF system.

For a high power transmitter, a power RF amplifier is used on the Tx side, while the Rx side uses an RF LNA that may be integrated into the receiver. With the range of electronic components and ICs on the market, your options are practically endless. The signal chain for an RF front end contains the stages shown below:

Many transceiver ICs or fully-integrated front-ends will have this type of block diagram. On the Rx side, the RF LNA needs to bring the signal level up to a suitable level for demodulation and normally runs well below saturation. Meanwhile, the RF power amplifier on the Tx side is normally run very close to saturation to try and maximize power output in the desired frequency range. RF mixers are a common component in the conversion and modulator/demodulator stages in an RF front end.

Finally, an antenna switch is used to swap between Rx and Tx legs of the signal chain. In systems with MIMO, multiple antenna switches get used to send signals to different amplifier stages on Tx (Rx) lines, and modulation (demodulation) will be performed upstream (downstream) from the switching stages.

Important RF Amplifier Specifications

There are many RF amplifier specifications to pay attention to as these will impact the quality of the received/demodulated signal. In this RF amplifier selection guide, I want to focus on the three most important specifications needed for any RF system operating over a broad frequency range. These should form the starting point for selecting an RF amplifier.

Bandwidth and Gain

These are probably the most important specifications you’ll need to consider when selecting an RF amplifier. RF amplifiers are normally advertised in terms of their gain at a specific frequency, or their bandwidth. These terms can be summarized as a gain-bandwidth product with a cutoff frequency. Even if the bandwidth is much larger than the desired frequency range, you can still cut off noise in the system and limit the bandwidth with a band-pass filter.

3IP Point and 1 dB Compression Point

The 3rd-order intercept point (OIP3) applies to any frequency-modulated signal and is related to the 1 dB compression point. This specification becomes important in power amplifiers on the Tx side as these amplifiers normally operate very near saturation. The nonlinear nature of the amplifier will create intermodulation products, with the 3rd order products being the most important. At some input power in the saturation regime, the 3rd order products would extrapolate to the same intensity as the desired sidebands.

When looking at a datasheet, pay attention to the power output at the 1 dB compression point rather than the OIP3 point as this is effectively the maximum power you can get out of the amplifier with minimum distortion. The 3IP point is still important as different standards place limits on allowed intensity of intermodulation products. The 1 dB compression point tends to lie about 10 dB below the 3IP point.

Noise Figure

Noise is inevitable in any electronic system, including RF signal chains. The noise figure in an RF amplifier basically tells you how input noise is amplified due to gain in the amplifier. There will be some decrease in the signal-to-noise ratio between the input and output, which will be unavoidable. This will also be some function of the bandwidth in the system, which is one reason to limit the bandwidth with a higher-order bandpass filter.

Note that, on the Rx side, the LNA is not necessarily a different type of RF amplifier. It’s simply an amplifier that tends to provide a lower noise figure than other amplifiers with comparable specs. If you’re designing for the Rx side with an amplifier ICs, pay attention to the noise figure to ensure you capture a clean demodulated signal.

Gain Flatness

This is rather different from gain and bandwidth alone, although still related. If you’re designing something like a dual-band system or a system that needs to sweep across a range of frequencies, you want to ensure the gain curve is relatively flat throughout the desired bandwidth. In other words, an amplifier’s gain is a function of frequency, thus noise figure is also a function of frequency. Gain flatness may be specified as a +/- variance or in dB (compared to average gain).

Other Important Specifications and Components

Other important specifications include package/footprint, operating temperature, ESD protection, phase flatness, and linearity (for LNAs) in the desired bandwidth. The last of these can be frequency-dependent, particularly in wideband RF amplifiers. Some other important components you’ll need include:

• Analog-to-digital converters

• RF antennas

• Passives for matching networks

To learn more about some other specifications that are relevant for general-purpose amplifiers, take a look at this article on the Octopart blog.

The specifications shown in this RF amplifier selection guide can vary widely for different components you’ll find on the market. When you need to find new components for your next product, try using the advanced search and filtration features in Octopart. When you use Octopart, you’ll have a complete solution for sourcing and supply chain management. Take a look at our integrated RF semiconductors page to start searching for the components you need.

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