Low Noise Amplifiers

Advantages of Chip-and-Wire Amplifiers over MMIC Designs for RF Applications

Executive Summary

Selecting the optimal amplifier technology has a significant impact on RF system performance in communications, radar, aerospace, and instrumentation applications. This white paper compares traditional chip-and-wire amplifier assemblies with monolithic microwave integrated circuit (MMIC) designs, highlighting their distinct performance advantages in critical areas, such as low noise amplifiers (LNAs), ultra-low phase noise amplifiers, and high-linearity amplifiers and supports these findings with real-world examples and quantitative data.

Introduction

The choice of amplifier technology can significantly affect system effectiveness, reliability, and longevity. While MMIC amplifiers are widely adopted for standardized, high-volume applications, chip-and-wire amplifier assemblies deliver unmatched customization and superior performance. Advantages that are especially valuable in specialized or performance-critical RF systems.

Key Performance Advantages

1. Superior Low-Noise Amplifier (LNA) Performance: Chip-and-wire amplifier assemblies give engineers the flexibility to select discrete transistors and precisely matched passive components, explicitly optimized for minimal noise figures. With careful hand-selection and meticulous tuning, these assemblies consistently achieve lower noise figures than typical MMIC counterparts. This translates directly into enhanced sensitivity and improved system-level performance, especially in radar and communication systems.

Example: A radar system using chip-and-wire technology achieved a lower noise figure of just 1.2 dB over a narrower targeted bandwidth. In contrast, a comparable MMIC solution delivered 2.1 dB but was designed for a much broader bandwidth, sacrificing noise figure for coverage. The lower NF of the chip-and-wire approach translated into a dramatically enhanced target detection range.

2. Exceptional Ultra-Low Phase Noise Amplifiers: In applications demanding precise signal integrity, such as high-frequency defense targeting and advanced radar systems, chip-and-wire solutions often outperform their MMIC counterparts. Their discrete construction enables fine-tuned optimization of both transistor selection and circuit layout, significantly reducing residual and additive phase noise across the RF chain.

Example: Testing has shown that chip-and-wire designs deliver residual phase noise improvements of up to 10 dBc/Hz (at a 10 kHz offset) compared to similar MMIC designs.

3. Enhanced High Linearity Amplifiers: Depending on the high linearity performance requirements, second-order harmonic behavior may provide distinct advantages over third-order two-tone levels, particularly when suppression of even-order harmonics is critical. Ultra-high linearity chip-and-wire amplifier designs often employ multiple push pull and Darlington circuits to cancel these harmonics, delivering effective out-of-band harmonic filtering. This prevents unwanted harmonic energy from crowding the fundamental and generating in-band spurious signals.

Example: A major defense contractor upgrading an over-the-horizon threat detection radar required IP2 performance levels not typically achievable with traditional MMIC designs. A standard 16-transistor hybrid chip-and-wire design delivered +100 dBm (IP2 two-tone), enabling the team to eliminate additional filters previously needed to suppress even order harmonics.

Customization and Adaptability

Modern chip-and-wire amplifier circuits deliver inherent advantages through their extensive customization potential. Unlike MMIC amplifiers, where integration can restrict optimization, chip-and-wire amplifier designs provide unmatched adaptability, enabling engineers to fine-tune every parameter to exact system requirements. This flexibility ensures maximum compatibility and improved performance across a wide range of RF systems and applications.

Reliability and Thermal Management

Chip-and-wire amplifiers inherently deliver superior thermal management, thanks to precise component-to-package placement and advanced surface-mount engineering. This improved heat dissipation leads to higher mean time between failures (MTBF), a critical advantage in demanding aerospace and defense applications.

Cost-Benefit Analysis

While MMIC designs may appear on the surface to be economically attractive initially for high-volume standard applications, chip-and-wire amplifiers deliver enhanced performance and reliability over time. Their superior operational lifetime, reduced maintenance requirements, and improved performance metrics often offset initial investment differences, proving highly cost-effective in specialized markets such as defense, aerospace, and critical communication infrastructures.

Conclusion

Chip-and-wire amplifier assemblies consistently outperform MMIC designs in key areas, including low noise, ultra-low phase noise, and high linearity. With the ability to be precisely optimized and engineered for superior reliability, chip-and-wire technology stands out as the clear choice for high-performance RF amplifier applications.

Download the PDF: Advantages of Chip-and-Wire Amplifiers over MMIC Designs for RF Applications

How are gain and noise figure related for low noise RF amplifiers?

In a low-noise amplifier (LNA), gain and noise figure are interrelated but distinct parameters. Generally, they exhibit an inverse relationship, improving one can often degrade the other, depending on the design trade-offs involved. Although gain and noise figure are optimized independently, achieving a high gain in the first stage of an amplifier is particularly beneficial, as it minimizes the contribution of noise from subsequent stages.

How does gain compare to noise figure on a single-stage LNA design?

The noise figure (NF) of an amplifier is defined as the ratio of the input signal-to-noise ratio (SNR) to the output SNR. A lower noise figure indicates better noise performance. One way to reduce NF is by operating the amplifier’s transistors near their maximum current capacity, which increases the signal amplitude relative to the amplifier’s intrinsic noise sources, thereby improving the output SNR.

As amplifier gain increases, both the signal and the internally generated noise are amplified. However, when the gain is sufficiently high, the input noise becomes the dominant contributor to the total noise, effectively reducing the relative impact of the amplifier’s own noise. This behavior is quantified by the Friis formula (or Friis equation), which describes how noise figure accumulates in cascaded amplifier stages.

In practical system design, placing a high-gain, low-noise amplifier (LNA) at the front end, ideally as close as possible to the antenna, significantly minimizes the influence of noise from subsequent stages. For this reason, the first-stage LNA typically has the most stringent noise and gain specifications in the entire receive chain.

Download PDF: How are Gain and Noise Figure Related?

Why GaAs Offer Better Noise Figure Performance than Silicon Transistors

Gallium arsenide (GaAs) transistors offer better noise figure performance than silicon transistors, due to several material influences, which include:

• High electron mobility
• Low intrinsic carrier concentration
• Semi-insulating substrate

Let’s examine these in greater detail.

1. Higher Electron Mobility

Electron mobility is a measure of how fast electrons move through a semiconductor material when excited by way of an electric field. gallium arsenide (GaAs) has a particularly high electron mobility over its silicon competitor (up to 6x greater) due to several distinct advantages. GaAs has a lower electron effective mass, which allows electrons to accelerate at a much higher speed through both the material and the electric field, which means they spend less time exposed to these “noisy regions” and are less likely to be influenced by its side effects. 

The way GaAs atoms are arranged influences mobility as well. Gallium arsenide’s crystal lattice is somewhat open compared to its silicon competitor, which has a denser diamond-packed cubic structure. This open structure allows electrons to move with fewer electron scattering impacts and events. Collisions with imperfections in the structure cause electrons to lose energy, which slows their forward progress, leading to higher thermal noise.

Gallium arsenide is also a direct band gap semiconductor; unlike its Silicon competitor is an indirect bandgap semiconductor. With a direct band gap advantage, electrons enter and then move in the conduction band without a loss of energy, which boosts mobility. Silicon, on the other hand, requires additional energy to move in the conduction band, which impedes free electron flow and lowers mobility (higher noise).

2. Low Intrinsic Carrier Concentration

Gallium arsenide offers a smaller band gap than its silicon competitor, thus requiring less thermal energy to move an electron from the valence band to the conduction band. This lower energy requirement for gallium arsenide electrons means that random thermal vibrations (temperatures above cold) create a much larger number of electron-hole pairs compared to a material with a larger band gap like silicon.

This process of silicon electrons being thermally excited and then recombining with holes creates an unstable and constantly fluctuating number of carriers. This unstable and constantly changing population is and of itself, electrical noise. A higher population of carriers leads to an inconsistent and greater current instability, and thus higher noise for the silicon transistor.  

3. Semi-Insulating Substrate

Gallium arsenide has a low parasitic capacitance compared to silicon. This coupling minimizes noise that would normally travel from the transistor to other parts of the circuit. Silicon, on the other hand, has a higher parasitic capacitance over gallium arsenide, which offers the opposite effect: higher capacitance equals higher noise figure. Gallium arsenide is, by nature, a semi-insulating substrate. GaAs substrates have lower capacitance to ground, thus lower noise figure.

GaAs Derivatives

Derivatives of a pure gallium arsenide structure include high electron mobility transistors (HEMTs), including a blend of gallium arsenide and aluminum gallium arsenide to channel electron movement into a further confined narrow layer, by design, improves electron flow, reduces electron scattering, and thus improves electron mobility.

A second generation of GaAs derivatives is a Pseudomorphic High Electron Mobility Transistor (pHEMT) that uses a blended layer of Gallium arsenide and Indium Gallium arsenide to achieve an even higher electron mobility performance. The InGaAs layer is grown onto the GaAs substrate, but doesn’t perfectly match the adjacent lattice. This results in a higher energy “barrier” between the channel and the donor layer. That higher barrier yields improved electron confinement and electron channeling, restricting electron movement to a much more tightly controlled channel this lowering electron scattering, fewer collisions, and lower thermal noise over HEMTs and traditional GaAs solutions.

Download the PDF: Why GaAs Offer Better Noise Figure Performance than Silicon Transistors

Different transistor technologies for low noise amplifiers (LNAs) exhibit distinct performance characteristics, primarily driven by their material properties and device structures. The key tradeoffs involve noise figure, frequency capability, cost, and power handling.

Silicon-Based Transistors

Silicon transistors remain the most widely used due to their abundance, mature fabrication infrastructure, and low cost. High-purity silicon wafers with very few defects are produced at scale, enabling integration into complex circuits.

• Performance: silicon-based LNAs typically operate at lower RF frequencies, up to the L-band; widely used in consumer applications such as Wi-Fi and Bluetooth
• Limitations: silicon bipolar transistors suffer performance degradation at higher frequencies due to lower electron mobility compared to compound semiconductors such as GaAs; higher parasitic capacitances and poorer noise figures further limit their suitability in high-frequency, ultra-low-noise circuits
• Advantages: silicon devices are highly cost-effective and allow seamless integration into system-on-chip (SoC)and system-in-package (SiP)solutions

Gallium Arsenide (GaAs) FETs

GaAs is a compound semiconductor with significantly higher electron mobility than silicon, making it well-suited for microwave circuits.

• Performance: GaAs MESFETs provide lower noise figures and higher frequency capability than silicon devices, making them ideal for cellular and satellite communications
• Limitations: GaAs devices are more expensive and mechanically brittle; lower bandgap reduces power handling capability and makes them more prone to voltage breakdown

PseudomorphicHigh-Electron-Mobility Transistors (pHEMTs)

pHEMTs are a class of HEMTs typically grown on GaAs substrates, incorporating a strained ("pseudomorphic") layer that enhances electron mobility.

• Performance: pHEMTs deliver superior noise figure performance compared to standard GaAs FETs or silicon devices, particularly above the HF band; have become the industry standard for LNAs requiring ultra-low noise performance from VHF through Ka-band
• Substrate Variations: some advanced pHEMTs incorporate InP channels on GaAs substrates, further improving electron mobility and noise performance

Indium Phosphide (InP) Transistors

InP-based devices represent the highest-performing option among the four technologies, offering unparalleled noise and frequency characteristics.

• Performance: with extremely high electron mobility, InP transistors achieve the lowest noise figures and highest gains at millimeter-wave and sub-THz frequencies, exceeding 100 GHz
• Specialized Use: due to their cost and complexity, InP LNAs are typically deployed in demanding applications such as radio astronomy, military radar front ends, and high-frequency test and measurement equipment
• Drawbacks: despite their superior performance, InP devices are fragile, costly to manufacture, and prone to lower breakdown voltages compared to GaAs or silicon technologies

Metallization and Fabrication Effects

Beyond the base semiconductor material, metallization choices and fabrication techniques strongly influence transistor noise performance.

• Parasitic Resistance: The resistance of the contact points, especially gate resistance, can be a significant source of thermal noise. Bu using low-resistivity metals like gold, one can minimize this extrinsic added noise source.
• Layout and Design: Careful layout design in order to minimize parasitic contributions is crucial in low noise figure circuit design. Reducing trace and hybrid bond wire lengths and ensuring proper ground planes using thick gold traces all help to reduce noise figure performance. Smaller gate lengths on some modern transistor designs can also improve the noise figure performance.
• Feedback and Matching Networks: Improved impedance matching as well as loop and feedback circuits around the transistor based circuit also affects the overall noise figure of the low noise amplifier.

Technology Comparison Summary

Download the PDF: Transistor Technologies for Low Noise Amplifiers (LNAs)

Spectrum Control specializes in the design and manufacture of hybrid chip and wire amplifiers. Class A amplifiers differ significantly from their Class AB counterparts. In Class A designs, the devices are biased to conduct current throughout the entire input signal cycle. While this approach delivers exceptional spectral fidelity, it comes at the cost of efficiency, as the amplifier operates at a continuous 100% duty cycle. By contrast, Class AB amplifiers represent a middle ground between Class A and Class B operation. They are biased to conduct for more than half (180°) of the waveform, improving efficiency while reducing the distortion that is typical in pure Class B designs.

Download PDF: Class A vs. Class AB Operation

RF Amplifier Linearity and Noise

IP3 and IP2 values are measurements of an amplifier’s linearity. They indicate how much non-linear distortion the amplifier produces and how that distortion contributes to the output signal.

Although both IP3 and IP2 quantify distortion, they differ in the type of distortion measured and the impact on overall system performance. In general, higher IP3 or IP2 values correspond to greater linearity and better amplifier performance.

A “linear” amplifier increases the strength of the input signal without altering its original shape. In other words, the output signal is an exact scaled replica of the input. This characteristic is critical in applications that require high spectral fidelity, such as communication systems and precision instrumentation.

To better understand linearity and non-linearity, consider a real-world analogy using a guitar and a frequency generator.

A frequency generator is a highly linear system designed to produce a simple, “pure” tone. Playing a Middle C produces a single sine wave at approximately 261 Hz. In this system, the output amplitude is directly proportional to the input voltage, raising the input simply increases the output level. The resulting waveform is clean and consists of only one frequency.

By contrast, a guitar is inherently non-linear. When a string is plucked to produce Middle C, it does not vibrate solely at its fundamental frequency. Instead, it also generates vibrations at integer multiples of that frequency, known as harmonics. The pluck (input) produces a complex output waveform containing both the fundamental and its harmonics, resulting in a rich and natural tone.

In this analogy, the amplifier’s role is similar to how the intensity of the pluck affects the sound. A harder pluck increases loudness but also changes the harmonic balance, introducing additional distortion. These harmonics, integer multiples of the fundamental, create the overtones that shape the timbre of the sound.

Nonlinearity in the guitar arises from several factors that interact in complex ways: the stiffness of the strings, the material of the body, and the playing technique. Each introduces deviations from ideal harmonic behavior. This nonlinearity makes the guitar sound warm and expressive, whereas the frequency generator produces an artificial, sterile tone.

In this analogy, the amplifier’s role is similar to how the intensity of the pluck affects the sound. A harder pluck increases loudness but also changes the harmonic balance, introducing additional distortion. These harmonics, integer multiples of the fundamental, create the overtones that shape the timbre of the sound.

Nonlinearity in the guitar arises from several factors that interact in complex ways: the stiffness of the strings, the material of the body, and the playing technique. Each introduces deviations from ideal harmonic behavior. This nonlinearity makes the guitar sound warm and expressive, whereas the frequency generator produces an artificial, sterile tone.

In amplifiers, similar effects occur. Nonlinearities cause the output signal to deviate from a perfectly scaled version of the input. These distortions can originate from the amplifier’s fundamental design, component quality, or operating environment. When an amplifier operates nonlinearly, frequencies within the input can mix, producing new frequencies that are the sums and differences of the original ones. These intermodulation products are unwanted because they are not harmonically related to the original signal.

No amplifier is perfectly linear, every RF component exhibits some degree of nonlinearity and will eventually reach a point of saturation where the output can no longer increase proportionally with the input. For this reason, linear amplifiers are designed to operate within a specified range where their linearity and thus IP2 and IP3 performance is optimized.

What is an Intercept Point?

• The intercept point is a mathematical construct used to describe an amplifier’s linearity. It represents the theoretical input power level at which the power of the desired output signal and the power of the distortion products (typically intermodulation products) would be equal.

• A higher IP2 or IP3 value indicates a more linear device and greater resistance to distortion, meaning the amplifier can handle stronger input signals before nonlinear effects become significant.

• In practice, amplifiers reach their 1 dB compression point (P1dB) and begin limiting output power well before the intercept point is actually achieved. The intercept point is therefore used as a figure of merit rather than a directly measurable condition.

Why is IP3 more important than IP2?

Third-order distortion products typically appear very close to the fundamental signal frequencies, making them difficult to suppress using standard filtering techniques. These unwanted signals can fall directly within the receiver’s operating band, degrading sensitivity and overall performance.

For this reason, IP3 is often considered the most critical linearity parameter for a receiver. It directly reflects the system’s ability to maintain clean signal integrity and operate effectively in environments with strong, closely spaced signals, such as crowded or high-interference frequency bands.

When is IP2 more important than IP3?

IP2 is generally less critical than IP3 in superheterodyne receivers because second-order distortion products typically fall outside the desired signal band and can be filtered out more easily.

However, IP2 becomes crucial in direct-conversion (zero-IF) receivers, where second-order distortion can create unwanted DC offsets or low-frequency artifacts that directly interfere with the desired signal. In such architectures, maintaining a high IP2 is essential to ensure accurate demodulation and minimize baseband distortion.

Download the PDF: IP3 vs. IP2