- The noise figure (F) is independent of the load resistance RL (this is a
general property of two-port networks) . However,
F is dependent on the generator resistance Rg.
- The output SNR is independent of the load resistance RL.
- The power gain Gp is independent of the transformer ratio.
- The SNR at the input is independent of both the transformer ratio n and the input resistance R1.
- Noise figure is independent of modulation, input power level, and bandwidth.
- As the bandwidth increases, the input and output SNRs decrease (by the same factor) and the noise figure does not change.
For a given input impedance R1 and generator impedance Rg, the following conditions are met when
the generator is impedance matched to the input impedance (i.e. when Rg=R1/n2):
- The transducer power gain is maximized.
- The available power gain in maximized.
- The voltage gain is maximized.
- The power delivered to the load is maximized.
- The power available from the network is maximized.
- The noise figure F is NOT in general minimized for the matched condition.
This is because the internally generated noise from the amplifier (i.e.
thermal noise generated by R1)
is dependent on the generator resistance.
- Op Amp Noise Figure: Don't Be Mislead
- Mohr on Receiver Noise
- ADC Noise Figure - An Often Misunderstood and Misinterpreted Specification
- Noise in continuous wave modulation systems
- Op Amp Noise Analysis
- Op Amp Noise
- Op Amp Total Output Noise Calculations for Single-Pole System
- Noise Analysis for High Speed Op Amps
- A Tutorial on Applying Op Amps to RF Applications
- Using High-Speed Op Amps for High Performance Design.
- Two-port Noise Lecture by Prof. Niknejad (Berkeley)
- J.S. Chitode, Communication Theory
- M.J. Ryan and M. Frater, Communications and Information Systems
- G. Gonzalez, Microwave Transistor Amplifiers
- B. Schiek, H. Siweris, and I. Rolfes, Noise in High-Frequency Circuits and Oscillators
- Op Amp Noise Calculator