Medium Power Amplifiers

What is a Chip and Wire Amplifier?

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

Executive Summary

Selecting the optimal amplifier technology significantly impacts RF system performance across 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 those found in low noise amps (LNAs), ultra-low phase noise amps, and high linearity amps, supported by real-world examples and quantitative data.

Introduction

The choice of amplifier technology can drastically influence system effectiveness, reliability, and longevity. While MMIC amplifiers are widely adopted for standardized, high-volume applications, chip-and-wire amplifier assemblies offer unmatched customization capabilities and superior performance metrics, especially beneficial in specialized or performance-critical RF systems.

Key Performance Advantages

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

Example: A radar system utilized chip-and-wire technology, achieving a lower noise figure of 1.2 dB for smaller targeted bandwidth, compared to a MMIC solution at 2.1 dB which was designed for a much broader bandwidth, appealing to a larger audience, sacrificing NF for bandwidth, thereby dramatically enhancing target detection range.

2. Exceptional Ultra-Low Phase Noise Amps: In applications requiring precise signal integrity — such as high-frequency defense related targeting and advanced radar systems—chip-and-wire methodologies more often excel over their MMIC counterparts. Their discrete construction allows detailed optimization of both transistor selection and circuit layout, significantly reducing residual and additive phase noise to the overall RF chain.

Example: In testing, chip-and-wire designs have demonstrated residual phase noise improvements up to 10 dBc/Hz or more (10 kHz offset) compared to comparable MMIC designs.

3. Enhanced High Linearity Amps: Depending on the type of High Linearity performance required, Second Order Harmonic performance might offer distinct advantages over Third Order Two Tone levels, depending on the even order harmonics that require suppression. Ultra-High Linearity Amp designs using chip & wire methodologies frequently incorporate multiple Push Pull and Darlington circuits to cancel even order harmonics, providing out of band harmonic filtering that can both crowd and corrupt the fundamental and thus causing in band spurious from out of band harmonics.

Example: A major defense contractor was upgrading an over the horizon threat detection radar and their system design team needed IP2 performance not normally available with traditional MMIC designs. A standard 16 transistor hybrid chip & wire design met levels of +100 dBm (IP2 Two Tone) allowing them to eliminate additional filters used to remove some even order harmonics.

Customization and Adaptability

Today’s chip-and-wire amplifier circuits incorporate inherent advantages in their extensive customization potential. Unlike MMIC amplifiers, where integration limits optimization, chip-and-wire amplifiers offer adaptability, allowing engineers to fine-tune each parameter precisely to system specifications. This customization ensures maximum compatibility and optimal performance across various RF systems and applications.

Reliability and Thermal Management

Chip-and-wire amplifiers inherently provide superior thermal management capabilities, owing to discrete component to package placement and advanced Surface-mount package engineering. Improved heat dissipation results in enhanced higher MTBF values, especially critical 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 can outperform MMIC designs across low noise, ultra-low phase noise, and high linearity metrics. By enabling precise optimization and providing superior reliability, chip-and-wire technology clearly emerges as the superior 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?

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

For a low noise RF amplifier, gain and noise figure are inversely related. Based on the parameter of interest, either one can be optimized through circuit design trade-offs. Even though gain and noise figure are distinct and separate parameters, a high gain on the first stage of an amplifier lowers the impact of Noise Figure on all the stages that follow.

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

The noise figure is the ratio of the input SNR to the output SNR. One way to achieve a low noise figure, by driving an amplifier’s transistors to maximum current capacity. Raising or increasing the signal level relative to the amp's own internal noise sources improves the output SNR, thereby improving the overall ratio.  As you increase an amp’s gain, any noise added by the RF amplifier is added to the signal and then, unfortunately, amplified like the rest of the signal. However, if you increase the amp’s gain, then any noise present in the input signal to the amplifier dominates and offsets the amp's own internal noise. The Friis formula or Friis equation describes the fundamental relationship between gain and noise in an LNA, where high gain supporting an LNA on an antenna, for example, essentially masks or hides the noise injected by other much noisier elements downstream. Therefore, the cleanest and lowest noise Figure LNAs are placed as close to the antenna as possible.

Understanding Impedance Matching

Load Termination Requirements

How important is a 50 Ohm termination?

A true 50 ohm termination is critical to the health of a small signal RF amplifier because it ensures a free-flowing signal propagation, maximum power transfer, and prevents damage from output reflections. If a 50 ohm amplifier is placed in an RF chain staring at a mismatched impedance, issues, including amp failure, might occur. The importance of impedance matching a 50 ohm, small signal amp with other components surrounding that amp cannot be overlooked; moreover, it is considered an industry standard of sorts.

• Maximum Power Output: when the input signal and load impedances are matched to 50 ohms, nearly all of the amplifier’s output power is delivered to the next cascaded chain component. In an unmatched or poorly matched system, some of that power is either reflected to the amp, as in the case of the amp looking into a mismatch, or reflected to the source, as in the case of a mismatch looking into the amp’s input.

• Preventing Signal Reflections: impedance mismatches cause signal reflections, this we know. This reflected signal then travels back along the signal path line and interferes with the output signal, creating stationary waves.

• Signal Integrity: stationary or standing waves can appear as current or voltage fluctuations along the signal path. This can manifest itself as distortion, a deterioration in the SNR, and seriously affect or degrade the output.

What are the consequences of a mismatch?

When a small signal RF amplifier operates in a chain with a mismatched impedance, the result of this load mismatch can range from a slight reduction in amp performance, all the way to reflections that can cause inoperable harm to the amplifier.

Reduced Performance

• Output Power Loss: looking at a small signal RF amplifier, for example, the output power, which is reflected from the load the amp is connected to, is merely lost energy. This waste reduces the total power output, which was intended to be delivered to the following component downstream. As the load mismatch gets worse, the intended output power loss increases dramatically.
• Distortion: when standing waves are present, as a result of load mismatch, the interference as a result of these stationary waves then distorts a byproduct, which degrades signal fidelity.
• Gain Loss: the gain of an amplifier in an RF chain can be lowered by load-mismatch losses at each gain block socket.

Can impedance mismatches damage an amplifier?

• Transistor Damage: when examining either an open (infinite impedance) or a short (zero impedance), all of the forward-looking output power is then reflected right back into the amplifier's output pin or output connector. This will cause a sudden and dramatic increase in either voltage or current directed at the transistors in the circuit. Designers, at times, will employ a diode to absorb that reflection, or a large cap to ground to drain it away, but not all those measures are 100% effective.
• MTBF: reflected power eventually has to be dissipated as heat if the mismatch is high enough.        This additional heat can affect the MTBF, shortening the life of the amplifier.

Can I prevent damage to an amplifier which has a poor mismatch?

• Share your Incident Impedance Measurements with the RF Amplifier Supplier: Knowing the mismatch issues before selection can help mitigate issues down the road. Spectrum Control can, at most times, place elements like diodes and pads on the output to help absorb, reflect, or condition those harmful mismatch reflections.
• Add a Pad: for reflection-sensitive amplifiers, a pad, maybe just ¼ dB to ½ dB (if there’s margin in the output power for a pad), can be strategically placed at the amp output or at the next component’s input to help reduce the degree of reflected power.
• Use Proper Load During the Test Phase of the Design: always terminate an amplifier with a load that matches a 50 ohm impedance. In test sessions, this means using a 50 ohm dummy load. In a system-level evaluation, this requirement extends to the entire RF chain, including connectors, cables, and any other element in the chain.