Narrow-Band LNA Designs in RF Receiver Front End

Key Takeaways

• The performance of an RF receiver is significantly influenced by the Low Noise Amplifier (LNA).  The received signals are usually weak and noisy and they need to be strengthened before applying to the next stage. This requirement makes LNA an integral part of the receiver front end. 

• By placing an inductor in the source of CS stage, Inductive Source Degenerated CS configuration is obtained. Most of the conventional narrow-band LNA circuits are the Inductive Source Degenerated CS type. 

• CG LNA consumes low power and is stable and robust against parasitic elements. The noise performance of the CG configuration is poor compared to the CS configuration.

RF receiver front end.

The performance of an RF receiver is significantly influenced by the Low Noise Amplifier (LNA).  The received signals are usually weak and noisy and they need to be strengthened before applying to the next stage. This requirement makes LNA an integral part of the receiver front end. Depending on the application, the LNA can be of wide-band or narrow-band. The narrow-band LNA is used for amplifying a single frequency or a small band of frequencies with a high voltage gain. 

There are several configurations of narrow-band LNA design available, so the selection of proper narrow-band LNA is very crucial. The optimization of the design selected is also important in LNA. Here in this article, we will review some narrow-band LNA designs. 

Major Narrow-Band LNA Designs in CMOS Technology

The demand for portable high-frequency communication devices established the widespread use of CMOS-technology-based integrated circuits. The standard CMOS technology has revolutionized the transceiver circuits in communication systems. Narrow-band LNA is the building block of any such CMOS-based receiver. According to the configuration, the CMOS LNA design can be classified as follows:

Common Source (CS) LNA

CS  LNA with inductive source degeneration.

This configuration exhibits high gain and good noise performance. By placing an inductor in the source of CS stage, Inductive Source Degenerated CS configuration is obtained. Most of the conventional narrow-band LNA circuits are the Inductive Source Degenerated CS type. 

When a resistor is placed in the feedback network of CS LNA, it transforms to CS LNA with a feedback resistor. It is not a well-known narrow-band configuration compared to inductive source degenerated CS LNA due to improper impedance matching and inability to operate at high frequencies. It allows a wide range of frequency bands with proper impedance matching and finds application in wide-band receiver circuits. 

CS  LNA with a feedback resistor

Common Gate (CG) LNA

This type of circuit consumes low power and is stable and robust against parasitic elements. The noise performance of the CG configuration is poor compared to the CS configuration. This configuration is widely used for wide-band LNA applications.

Cascode LNA

Cascode narrow-band LNA. 

Cascode LNA offers high power gain, low power consumption, good noise performance, and high reverse isolation. The cascode amplifier is suitable for narrow-band applications. With feedback techniques, the cascode LNA can be converted into multi-band or wide-band LNAs. The narrow-band LNA given in the figure above combines the benefits of both cascode CS LNA and CS LNA with inductive source degeneration. It is the most prevalent configuration used in communication engineering circuits. 

Cascaded narrow-band LNA. 

Cascaded Narrow-Band LNA

The figure above represents cascaded and cascoded LNA with inductive source degeneration. The inductive source degeneration is employed for input impedance matching. The LNA is cascaded for increasing the power gain, whereas the cascode topology increases the bandwidth of the circuit. The impedance matching in LNA is achieved by connecting matching circuits at the input and output end of the LNA design. This configuration showcases low power consumption, high gain, reduced noise, and better stability. 

Narrow-band LNA design is a significant part that is capable of reducing the noise figure of the RF receivers. With the incorporation of well-designed and optimized narrow-band LNA, the receiver gives a good signal-to-noise ratio in the prescribed single frequency or band of frequencies. For portable communication devices, there is always a need to construct narrow-band LNA circuits with low power consumption, good noise rejection, better stability, and high gain. 

Cadence's PCB Design and Analysis tools can support you in your system design and analysis projects. Subscribe to our newsletter for the latest updates. If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.

Figure Courtesy

1. CS  LNA with inductive source degeneration and CS  LNA with a feedback resistor

L. Vimalan and S. Devi, “Performance Analysis of Various Topologies of Common Source Low Noise Amplifier (CS-LNA) at 90nm Technology,” in 2018 3rd IEEE International Conference on Recent Trends in Electronics, Information & Communication Technology (RTEICT), Bangalore, India, May 2018, pp. 1687–1691, doi: 10.1109/RTEICT42901.2018.9012326.

2. Cascode narrow-band LNA 

T. Mohammadi, A. Ghaneizadeh, and Y. Mafinejad, “A Narrow-Band CMOS LNA for Wireless Communications,” in Electrical Engineering (ICEE), Iranian Conference on, Mashhad, May 2018, pp. 265–268, doi: 10.1109/ICEE.2018.8472434.

3. Cascaded narrow-band LNA 

A. R. Neeraja and S. S. Yellampalli, “Design of cascaded narrow band low noise amplifier,” in 2017 International Conference on Electrical, Electronics, Communication, Computer, and Optimization Techniques (ICEECCOT), Mysuru, Dec. 2017, pp. 1–4, doi: 10.1109/ICEECCOT.2017.8284642.