Input

  • Gen AC amplitude [V]: Vg =
  • Gen resistance [Ω]: Rg =
  • Load resistance [Ω]: RL =
  • Input resistance [Ω]: R1 =
  • Output resistance [Ω]: R2 =
  • Voltage gain parameter: A =
  • Bandwidth [Hz]: BW =
  • Transformer turns ratio: n =


Simple amplifier

Output

Power

  1. Power avail from source: PAVS= [dBm]
  2. Input power: PIN= [dBm]
  3. Power delivered to load: PL= [dBm]
  4. Power avail from network: PAVN= [dBm]

Gain

  1. Transducer pwr gain: GT = PL/PAVS = [dB]
  2. Power gain: Gp = PL/PIN = [dB]
  3. Avail power gain: GAV = PAVN/PAVS = [dB]
  4. Voltage gain: Gvoltage = Vout/Vg = [V/V]

Noise

  1. Avail noise power at input Ni= [dBm]
  2. Avail noise power at output N0= [dBm]
  3. Actual total noise pwr at output N0,out= [dBm]
  4. Input SNR: PAVS/ Ni = [dB]
  5. Output SNR: PAVN/N0= [dB]
  6. Output SNR (Alt. definition): PL/N0,out= [dB]
  7. Noise figure: F = [dB]

Observations

  1. The noise figure (F) is independent of the load resistance RL (this is a general property of two-port networks) [15]. However, F is dependent on the generator resistance Rg.
  2. The output SNR is independent of the load resistance RL.
  3. The power gain Gp is independent of the transformer ratio.
  4. The SNR at the input is independent of both the transformer ratio n and the input resistance R1.
  5. Noise figure is independent of modulation, input power level, and bandwidth.
  6. As the bandwidth increases, the input and output SNRs decrease (by the same factor) and the noise figure does not change.
  7. 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.

References

  1. Op Amp Noise Figure: Don't Be Mislead
  2. Mohr on Receiver Noise
  3. ADC Noise Figure - An Often Misunderstood and Misinterpreted Specification
  4. Noise in continuous wave modulation systems
  5. Op Amp Noise Analysis
  6. Op Amp Noise
  7. Op Amp Total Output Noise Calculations for Single-Pole System
  8. Noise Analysis for High Speed Op Amps
  9. A Tutorial on Applying Op Amps to RF Applications
  10. Using High-Speed Op Amps for High Performance Design.
  11. Two-port Noise Lecture by Prof. Niknejad (Berkeley)
  12. J.S. Chitode, Communication Theory
  13. M.J. Ryan and M. Frater, Communications and Information Systems
  14. G. Gonzalez, Microwave Transistor Amplifiers
  15. B. Schiek, H. Siweris, and I. Rolfes, Noise in High-Frequency Circuits and Oscillators
  16. Op Amp Noise Calculator