805 Overcoming the Challenge of Noise in RF Systems

Brief summary of the scope of this course:

• Origins of electrical noise;
• RF Systems;
• Overview of some “special” devices and components;
• Signal to noise power ratio (S/N);
• Digitally-modulated systems: Shannon and BER;
  • Fundamental noise considerations: Noise power and Noise floor;
  • Signal to noise+distortion ratio (‘SINAD’);
  • Noise factor and noise figure;
  • Equivalent noise temperature T_e;
  • Minimum Detectable Signal;
• Noise figure for an Attenuator;
• Sources of noise in transistors;
• Phase noise: and the (modified) Leeson formula.
• Frequency dependence of noise figure: ‘real-life’ examples
• Overall noise figure for cascaded blocks
              Analytical results;
              Practical examples.
• Noise-matching and narrowband LNA design
• Broadband LNA design: CAD optimization
• Practical examples of LNAs (mainly MMICs)
• Parametric amplifiers
               Rationale and fundamental considerations;
               Analytical results;
               Possible implementation in quantum computers
• Noise Considerations for Transmitters

From Day 2 onwards set Assignments form major learning exercises.

In More Detail

• How electrical noise basically originates, examples: during the conversion processes (analog-to-digital and vice-versa), thermally (including resistors), random trajectories of electrons (notably semiconductor junctions – diodes and transistors of all types), random fluctuations of capacitance (e.g. “varactor” diodes) – and even from the sky hence entering antennas.

• Some generic types of RF systems:
  • Terrestrial communications (mainly cellular: 4G LTE, 5G);
  • Space-based systems (satellite communications, deep space systems;
  • Radars (AESAs, altimeters, road vehicle, sounding);
  • Quantum computers.

                         - Systems
                         - Subsystems
                         - Modules
                         - Circuits
                         - Components
                         - Materials

• From system down to circuit level in all instances noise is a potentially major hazard.
• More extensive examples of RF systems – with a focus on noise: (Mainly block diagram based, occasionally an annotated photograph).
  Note: LNAs (low-noise amplifiers – much more later…)

• Digitally-modulated schemes for radio systems (very important) – influence of noise. Probability of (received) bit error – or bit error rate (BER) – calculations and conclusions are provided. QPSK, mQAM

                          - Software-defined radio (SDR);
                          - Software-defined satellites (SDS);
                          - Terrestrial radio (UHF, microwave, millimetre-wave) – fixed wireless access (FWA) increasing adopting millimetre-wave; 
                          - High-altitude platforms (HAPS);
                          - Space-based systems (satellite communications, also deep space systems); Notably and increasingly constellations of LEOs
                          - Example: Following five years of trying late in 2021 Boeing finally obtained approval for its proposed V-band LEO constellation;
                                          - Radars: Basic considerations;
                                          - Active, electronically-scanned (AESAs).

• Quantum computers (some designs require cryogenic operation – very deep into noise although operating at extremely low temperatures).

• Overview of some “special” devices and components encountered in RF systems:

                          - Schottky diode;
                          - Varactor diode;
                          - 3-port ferrite circulator;
                          - Multi-cavity klystron (power tube – transmitters);
                          - Travelling-wave tube (TWT: power tube – wide-band transmitters)

Noise and Signal-to-Noise Ratio: Digitally-Modulated Systems

Noise in digitally-modulated receivers:

• Noise in ADCs: effective number of bits (ENOB)
• Quantization noise
• Effect of sampling jitter
• Energy per bit and noise spectral density (E_b and N₀)
• Spectral efficiency (bit/s/Hz)
• Channel capacity and the Hartley-Shannon theorem
                - Practical aspects.

Because of its importance in RF systems design we now focus on (simply) the average signal-to-noise power ratio: S/N – where each quantity is basically measured in Watts. Both quantities are quite readily measured. 

The received S/N is particularly important in digitally modulated receivers because it is a vital term in:

(i)                   Shannon’s theorem (provides a limiting result), and:
(ii)                 Probability of (received) bit error – or bit error rate (BER) calculations.

Examples: QPSK and “mQAM” (e.g. 256QAM)

• Quantitative expressions given to determine ‘BER’ for these modulation schemes.
• Major assignment for participants. Calculations for BERs under given closely-spaced S/N ratios
• Practical implications

Fundamental (Analytical) Noise Considerations:

• Noise power (full expression including quantum effects, simplified equation neglecting quantum effects);
• Noise floor – implications;
• Signal-to-noise ratio;
• Signal to noise+distortion ratio (‘SINAD’);
• Noise factor and noise figure;
• Equivalent noise temperature T_e;
• Minimum Detectable Signal;
• Practical examples.

 

Assignment for participants

• Noise figure for an Attenuator

• Sources of noise in a FET (quantitatively as far as possible)
  • Thermal (diffusion) noise;
  • Shot noise;
  • Flicker noise (“pink” or 1/f  noise);
  • Importance of transistor selection.

• Phase noise: general considerations. Application to oscillators and amplifiers. The (modified) Leeson formula.

Assignments for participants

• Frequency dependence of noise figure: ‘real-life’ examples

• Overall noise figure for cascaded blocks
  • Analytical results;
  • Practical examples.

• Noise-matching and narrowband LNA design
• Broadband LNA design: CAD optimization
• Practical examples of LNAs (mainly MMICs)

BUT: how can we (radically) aim to reduce noise down to very low levels?

• Parametric amplifiers
  • Rationale and fundamental considerations;
  • Analytical results;
  • Possible implementation in quantum computers

Major (challenging) Assignment for Participants

Noise Considerations for Transmitters

• General considerations;
• Sources of noise from various RF power devices (FETs, GaN HEMTs, klystrons and TWTs);
• A back-off measurement technique to determine transmitter noise.

Discussion.
Overview of the course.

 

Dr. Edwards has written a text that is a recommended reference.  The reference is not required for this course.

Title: “Technologies for RF Systems”
by Terry Edwards. Artech House UK. ISBN: 9781630814502,