Hearing a Whisper in a Noisy Room

Imagine standing in a crowded room, trying to hear someone whisper. If your hearing aid adds its own hiss, that whisper vanishes. An LNA works the same way in a receiver. It must amplify the weak signal from the antenna without smothering it with extra noise.

Introduction: Why Low-Noise Amplifiers?

In a wireless communication system, the transceiver has two main parts: the transmitter and the receiver. While transmitters get most of the attention for pushing out high-power signals, the receiver is equally important. It must capture signals that arrive at the antenna very weak after traveling through free space, reflections, and interference.

To make sense of these faint signals, the receiver relies on its very first active block, which is the Low-Noise Amplifier (LNA). The LNA’s mission is simple but decisive: boost the weak antenna signal while adding as little noise as possible. This step sets the foundation for everything that follows, feeding a cleaner and stronger signal to the mixer, baseband, and digital processing chain.

Because it determines whether the receiver can actually hear weak signals, the LNA is often called the gatekeeper of sensitivity. Without it, the rest of the receiver would be overwhelmed by noise, and even the most advanced processing could not recover the lost information.

Why Push LNAs to G-Band?

If LNAs already exist at lower microwave frequencies, why take them to the 140–220 GHz G-band where design is so difficult? Because that’s where the future of wireless and sensing lives:

• 6G communications: G-band offers tens of GHz of available bandwidth, enabling data rates well above 100 Gbps.
• Automotive radar: Operating near 160–200 GHz allows sub-centimeter resolution, crucial for next-gen driver assistance.
• Imaging & security: Higher frequencies improve material penetration and image sharpness.
• Remote sensing & space: Atmospheric absorption lines around 183 GHz are ideal for climate and weather monitoring.

In short, G-band LNAs are the front door to tomorrow’s high-frequency systems.

Why Is It Harder at G-Band?

Now, move this challenge into the 140 to 220 GHz range, known as the G-band. This is where next-generation communications, high-resolution imaging, and radar want to operate. But designing LNAs here is like building an ultra-sensitive stethoscope while standing next to a jet engine:

• Transistors provide limited gain at these extreme frequencies since they are operating close to their physical limits (fT and fmax).
• On-chip passives lose quality factor (Q): inductors and capacitors become lossy, adding noise.
• Parasitics dominate: capacitances at transistor nodes make noise matching harder.
• Even packaging matters: bond wires and pad parasitics can noticeably raise the measured NF.

A Glimpse of Our Work

At Neural Semiconductor, we focused on one of the toughest challenges in G-band design: achieving both a very low Noise Figure (NF) and strong linearity at extremely high frequencies. We designed two LNAs in IHP’s 130 nm SiGe BiCMOS technology:

• A 160 GHz LNA optimized for minimum noise figure and strong linearity.
• A 207 GHz LNA that extends operation deeper into the G-band with competitive noise performance.

These designs show how SiGe can achieve sensitive, power-efficient LNAs that are highly relevant for 6G, radar, and imaging systems.

In the next part, we will explore the fundamental parameters of LNA design and see how they guided our own G-band implementations. Are you ready to dive in?

References and Learning Resources

• Stärke, Paul, et al. "Common emitter low noise amplifier with 19 dB gain for 140 GHz to 220 GHz in 130 nm SiGe." 2019 International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob). IEEE, 2019.
• Coen, Christopher T., et al. "Design and On-Wafer Characterization of $ G $-Band SiGe HBT Low-Noise Amplifiers." IEEE Transactions on Microwave Theory and Techniques 64.11 (2016): 3631-3642.
• De Filippi, Guglielmo, et al. "A D-band low-noise-amplifier in SiGe BiCMOS with broadband multi-resonance matching networks." 2023 18th European Microwave Integrated Circuits Conference (EuMIC). IEEE, 2023.
• Moschetti, Giuseppe, et al. "A 183 GHz metamorphic HEMT low-noise amplifier with 3.5 dB noise figure." IEEE Microwave and Wireless Components Letters 25.9 (2015): 618-620.