What is lna in rf?

State of the art Low Noise RF Amplifiers for a wide variety of applications are available from Castle Microwave. Our range of Low Noise Amplifiers and Ultra Low Noise Amplifiers have the following features:

• Frequencies ranging from 0.2GHz to 100GHz.

• Broadband and narrow bandwidth devices

• Single power supply

• Lightweight housing

• Appropriate coax or waveguide interfaces using a variety of technologies

Surface mount MMIC devices are also available as die or packaged parts.

A low noise amplifier is used to amplify very low-power signals without significantly degrading their signal-to-noise ratio. They increase the amplitude of weak RF signals, which assists processing as part of a receiver circuit. The primary specification parameter of an LNA is its noise figure, which is a measure of how much the LNA degrades the signal-to-noise ratio of the received signal.

Low noise amplifiers can also be used to compensate introduced loss in an RF signal path. By inserting a low noise amplifier, it will help to restore the original signal level, while ensuring the signal-to-noise ratio is retained.

What is a low noise amplifier? A low noise amplifier is used to amplify very low-power signals without significantly degrading their signal-to-noise ratio. They increase the amplitude of weak RF signals, which assists processing as part of a receiver circuit.

A low-noise amplifier (LNA) is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio. An amplifier will increase the power of both the signal and the noise present at its input, but the amplifier will also introduce some additional noise. LNAs are designed to minimize that additional noise. Designers can minimize additional noise by choosing low-noise components, operating points, and circuit topologies. Minimizing additional noise must balance with other design goals such as power gain and impedance matching.

LNAs are found in radio communications systems, medical instruments and electronic test equipment. A typical LNA may supply a power gain of 100 (20 decibels (dB)) while decreasing the signal-to-noise ratio by less than a factor of two (a 3 dB noise figure (NF)). Although LNAs are primarily concerned with weak signals that are just above the noise floor, they must also consider the presence of larger signals that cause intermodulation distortion.

Antennas are a common source of weak signals.[1] An outdoor antenna is often connected to its receiver by a transmission line called a feed line. Losses in the feed line lower the received signal-to-noise ratio: a feed line loss of 3 dB degrades the receiver signal-to-noise ratio (SNR) by 3 dB.

An example is a feed line made from 10 feet (3.0 m) of RG-174 coaxial cable and used with a global positioning system (GPS) receiver. The loss in that feed line is 3.2 dB at 1 GHz; approximately 5 dB at the GPS frequency (1.57542 GHz). This feed line loss can be avoided by placing an LNA at the antenna, which supplies enough gain to offset the loss.

An LNA is a key component at the front-end of a radio receiver circuit to help reduce unwanted noise in particular. Friis' formulas for noise models the noise in a multi-stage signal collection circuit. In most receivers, the overall NF is dominated by the first few stages of the RF front end.

By using an LNA close to the signal source, the effect of noise from subsequent stages of the receive chain in the circuit is reduced by the signal gain created by the LNA, while the noise created by the LNA itself is injected directly into the received signal. The LNA boosts the desired signals' power while adding as little noise and distortion as possible. The work done by the LNA enables optimum retrieval of the desired signal in the later stages of the system.

Low noise amplifiers are the building blocks of communication systems and instruments. The most important LNA specifications or attributes are:[2]

A good LNA has a low NF (e.g. 1 dB), enough gain to boost the signal (e.g. 10 dB) and a large enough inter-modulation and compression point (IP3 and P1dB) to do the work required of it. Further specifications are the LNA's operating bandwidth, gain flatness, stability, input and output voltage standing wave ratio (VSWR).

For low noise, a high amplification is required for the amplifier in the first stage. Therefore, junction field-effect transistors (JFETs) and high-electron-mobility transistors (HEMTs) are often used. They are driven in a high-current regime, which is not energy-efficient, but reduces the relative amount of shot noise. It also requires input and output impedance matching circuits for narrow-band circuits to enhance the gain (see Gain-bandwidth product).

Amplifiers need a device to provide gain. In the 1940s, that device was a vacuum tube, but now it is usually a transistor. The transistor may be one of many varieties of bipolar transistors or field-effect transistors. Other devices producing gain, such as tunnel diodes, may be used.

Broadly speaking, two categories of transistor models are used in LNA design: Small-signal models use quasi-linear models of noise and large-signal models consider non-linear mixing.

The amount of gain applied is often a compromise. On one hand, high gain makes weak signals strong. On the other hand, high gain means higher level signals, and such high level signals with high gain may exceed the amplifier's dynamic range or cause other types of noise such as harmonic distortion or nonlinear mixing.

The noise figure helps determine the efficiency of a particular LNA. LNA suitability for a particular application is typically based on its noise figure. In general, a low noise figure results in better signal reception.

The circuit topology affects input and output impedance. In general, the source impedance is matched to the input impedance because that will maximize the power transfer from the source to the device. If the source impedance is low, then a common base or common gate circuit topology may be appropriate. For a medium source impedance, a common emitter or common source topology may be used. With a high source resistance, a common collector or common drain topology may be appropriate. An input impedance match may not produce the lowest noise figure.

Another design issue is the noise introduced by biasing networks.

LNAs are used in communications receivers such as in cellular telephones, GPS receivers, wireless LANs (WiFi), and satellite communications.

In a satellite communications system, the ground station receiving antenna uses an LNA because the received signal is weak since satellites have limited power and therefore use low-power transmitters. The satellites are also distant and suffer path loss: low Earth orbit satellites might be 120 miles (190 km) away; a geosynchronous satellite is 22,236 miles (35,785 km) away.

The LNA boosts the antenna signal to overcome feed line losses between the antenna and the receiver.

LNAs can enhance the performance of software-defined radio (SDR) receiver systems. SDRs are typically designed to be general purpose and therefore the noise figure is not optimized for any one particular application. With an LNA and appropriate filter, performance is improved over a range of frequencies.

In a communication system, a low noise amplifier or LNA is an essential component in the receiver section. The main role of this amplifier is to amplify the weak signal by keeping the noise as small as possible. The performance of this amplifier can be measured most particularly by considering different factors like its noise figure, gain, dynamic range, matching, stability, and return loss. These amplifiers play a key role in millimeter-wave applications like passive remote sensing, Earth science radiometry, transceivers, and radio astronomy. This article provides brief information on Low noise amplifiers which are also called LNAs.

A low noise amplifier definition is an electronic amplifier that is capable of amplifying very weak signals & provides voltage levels appropriate for A/D conversion otherwise further analog processing. These amplifiers are used in applications where low amplitude sources involve transducers & antennae.

The working principle of a low noise amplifier is to amplify a low-power signal without degrading its S/N ratio. Generally, normal amplifiers amplify signals but they introduce additional noise to the system. So, LNA is used to reduce the noise. These amplifiers are found in electronic test equipment, medical instruments, and radio communications systems.

The specifications of the low noise amplifier are discussed below.

The gain of an LNA is the ability to amplify or increase the input signal level at a level that can be processed by the receiver. The gain is specified in dB and the typical gain values of LNA range from 10 to 30 dB.

The noise figure can be defined as the ratio of whole output noise power and the output noise because of the input source. The noise figure signifies the quality of amplifiers. The noise figure specifies the noise performance of an RF system and it is generally measured by using typical signal generators or noise generators. When the noise figure value is low then the RF system performance will be better.

Generally, the low noise amplifier amplifies both the signal & noise available at its input. Additionally, the output includes noise because of the low noise amplifier. This in turn decreases the S/N ratio. So a good LNA contributes extremely small noise that is <1.5dB.

The linearity of a low noise amplifier can be defined as a measure of amplifier capacity used to amplify the signal without distortion. Once this amplifier is operating linearly, then output power in dB is the amount of the input signal & the gain.

When the input signal of an LNA has -60 dBm amplitude then it operates linearly. But, once the input signal of the LNA is increased to 0 dBm, then LNA is nonlinear, then the output signal can be distorted, the gain is no longer 20 dB & the amplitude of the output signal is simply +5 dBm.

The maximum RF input level is the maximum signal level of LNA that can tolerate. At this input signal level, the low noise amplifier operation is non-linear. This quantity is most frequently specified in dBm. The maximum RF input level of LNA typically ranges from 18 to 20 dBm.

The difference between a low noise amplifier and a power amplifier includes the following.

In a communication system, the receiver section needs amplification for the weak signal which is received from the antenna. So this amplification can be accomplished through the main component called Low Noise Amplifier or LNA. The characteristics of this amplifier can be described by certain parameters like gain, noise figure, chip area, linearity, power consumption & bandwidth.

The block diagram of the low noise amplifier is shown below. The designing of a low noise amplifier can be done by using a common gate amplifier, active inductor & common drain stage. Generally, the common gate amplifier is mainly used at the input stage whereas the common drain amplifier is used at the output stage to provide the best input as well as output matching. The low noise amplifier is bound with particular characteristics like gain & noise figure but the selection of LNA mainly depends on some specific parameters like power supply, bandwidth, chip area & linearity.

The common gate (CG) amplifier forms the primary stage of the proposed LNA. By this stage, it is not much complex to get input impedance matching. This amplifier can be used as a current buffer or voltage amplifier.

An active inductor mainly includes CMOS transistors & its operation is simply the same as a passive inductor. This inductor is mainly designed to give good quality factors to determine its efficiency. The performance of this inductor can be enhanced by introducing dual feedback while designing the circuit.

Generally, a common drain amplifier is known as a buffer or a source follower. It is normally used at the output stage of the LNA design. This amplifier has less output impedance. So, it can provide good output impedance matching.

The proposed low noise amplifier design can be accomplished in 45nm CMOS technology. The LNA comprises 12 transistors, but using the least number of transistors within the design will be useful for decreasing the power consumption and parasitic effects.

In the above three-stage low noise amplifier, the common gate amplifier is used as an input stage. This amplifier is extensively used in wireless communications. First, this common amplifier receives a signal with noise from the antenna. The noise figure is somewhat high in this stage. This noise signal is transmitted to the next stage of the LNA like an active inductor.

In an active inductor, the noise of the received signal can be reduced because of noise-canceling & resistive degeneration. An active inductor is used to get low power consumption, reducing complexity. This low noise signal is given to the final stage of LNA like a common drain amplifier. This is also called a buffer or source follower. This amplifier is capable to obtain small output impedance matching. So this amplifier has potentially very less noise. In this way, the noise is reduced from input to output of LNA.

The circuit diagram of a low noise microphone pre-amplifier with NE5534 IC is shown below. In this circuit, alike NE55534 low noise amplifier IC is an essential component. The required components to build this circuit mainly include resistors like 10KΩ -2 and 68KΩ-2, capacitors like 1µF-1, 10µF-2, 100µF-1, 9V to 12V battery, audio jack-1, and electret microphone-1.

The main function of this low noise microphone pre-amplifier circuit is to amplify the weak audio signals. Once an audio source like the microphone has less sound range then this circuit is helpful in amplifying that low signal or weak signals & transmits that signal for further amplification.

The above circuit can be designed with an IC instead of a transistor because this IC will provide a much better distortion filter. This low noise amplifier IC includes low noise, high unity-gain, low power consumption with short circuit protection, and low harmonic distortion.

Here, the mic preamplifier specifications may change based on the mic used to capture the audio signals & the type of sound being recorded. The essential specifications to be considered within a pre-amplifier circuit are noise, distortion & gain.

This circuit operates with a 9V to 12V battery. Here, Electret Mic generates audio signals that are transmitted to the input of IC. Here you can use any audio source instead of a microphone.

This circuit’s overall voltage gain mainly depends on the resistors connected at the non-inverting terminal of the IC. The output signal which is generated from this IC can be transmitted through one more capacitor to filter out any noise.

This circuit is very useful where low noise audio preamplifier is necessary like live music, cellphones, soundcard within laptops, and audio recording applications.

Performance characteristics:

The most important performance characteristic of an LNA is its noise figure (NF). This is defined as the ratio of output noise power to input power:

NF = Pout / Pin

where Pin is the total input power (sum of all signals) and Pout is the total output power (sum of all amplified signals). Thus, if you increase Pout by 10 dB while keeping Pin constant, NF will decrease by 10 dB. In practice, however, it’s difficult to keep Pin constant when amplifying weak signals; usually Pin has to be increased significantly in order to have a Low Noise figure.

There are different types of low noise amplifiers like the following.

These low noise amplifiers mainly include SiGe LNA & Wideband LNA product families. SiGe-type LNAs are optimized for various supply currents. They offer low noise figures & absolute stability for Wideband & MMIC driver amplifiers LNA designs. Their optimized internal transistor cell arrangement leads to the best noise figures & power gains at high frequencies.

Wideband LNA design offers a variety of high-performance BFP products. These products utilize silicon germanium carbon bipolar technology for wireless applications. MMIC driver amplifiers use the Darlington configuration that offers a single package to RF designers.

These low noise amplifiers are very important when it comes to communication systems as well as future technologies. By including a low noise amplifier to the antenna, then the signal can be improved without adding extra surplus noise to the system. The main benefits of using these low noise amplifiers are; high linearity, Ultra-low noise figure & low current consumption that improves the signal sensitivity, enhances data transfer rate, increases system integration & power consumption can be reduced.

GNSS low noise amplifiers need a low or ultra-low noise RF amplifier and high linearity to improve the sensitivity of the receiver for best localization even in low battery or bad conditions. At present, most of smartphones have navigation applications, which impose even greater demands on size, linearity & power consumption as compared to stand-alone PNDs (personal navigation devices). These amplifiers improve signal sensitivity with very low current consumption and a wide range of voltage supply.

How to design a Low noise amplifier ?

A low noise amplifier can be designed using either a negative feedback topology or one without any feedback. The former approach is more commonly used because it can provide better performance when compared to an equivalent amplifier without feedback.

What is the purpose of a low noise amplifier?

. To increase the signal-to-noise ratio

. To increase the gain of an amplifier

. To remove unwanted noise from an electromagnetic wave

. To attenuate the input of an amplifier

What is the difference between noise and interference?

Noise is unwanted signal that can interfere with the operation of a circuit. It is usually caused by thermal agitation, voltage fluctuations, or other electrical effects. Interference is an unwanted signal that interferes with the operation of another circuit.

Please refer to this link to know more about DC Amplifier MCQs,  Low Noise Amplifier MCQs

The advantages of a low noise amplifier include the following.

The disadvantages of low noise amplifiers include the following.

The applications of low noise amplifiers include the following.

Please refer to this link to know more about Parabolic Reflector Antenna, Class D Amplifier.

Thus, this is all about an overview of a low noise amplifier or LNA. For the best working of these amplifiers, high gain and low noise figures are the main requirements. The efficiency of this amplifier can be determined by analyzing different parameters like noise figure, gain, stability, & linearity within the circuit. Here is a question for you, what is PA?