Fig 15—The mixing arrangement within the oscillator whereby the carrier frequency (fa), assumed noiseless, gets modulated with the various noise sources.
merical approach is considered to provide nonlinear analysis. It can be shown that the phase noise is composed of two parts.
• The near-carrier noise consists of contributions from the perturbation of the oscillating frequency caused by the noise sources at each side band frequency. This part is the major noise source at near-carrier frequencies.
• The far-carrier noise consists of contributions from each sideband noise source through sideband-to-sideband transfer functions. This part is similar to a mixer noise calculation and is the major noise source at frequencies far from the carrier.
Fig 14 shows that the oscillator noise consists of the near- and far-carrier noise.
The Noise Figure of the Mixing Circuit
In order to calculate the noise figure,
Nonlinear Device Noise Sources linear Subnetwork Noise Sources kH
Frequency s Conversion,
LO Signal Noise Source
Fig 17—Summary of IF noise contributions.
we assume that the pumped active device acts like a mixer circuit; we need to calculate the total internal noise of the circuit at the "IF" frequency.
Noise Analysis Step 1
Using a nonlinear simulator, we perform a harmonic balance analysis to determine the steady state of the mixer. Fig 15 shows the mixing arrangement.
The harmonic balance calculation of the nonlinear simulator determines the Fourier coefficients of the voltages and currents of the circuit. Any re ceiver configuration (eg, LNA's, AMP, etc) may be considered.
Noise Analysis Step 2
We next have to calculate the transfer functions of the sideband signals to the IF-band signal. Fig 16 shows a summary of noise sources mixed to the IF. The noise at each sideband frequency contributes to the noise at the IF through frequency conversion.
Fig 17 shows a summary of the IF noise contributions in a general nonlinear mixer circuit: note the large number of contributing elements which make up the total noise at the output. The calculation of dN is performed by Eq 42 where the intermediate steps are given in Note 6. (See also Notes 3-14.)
» , ,\VI< fd f }*(\%<fd f ) - 2 Re((V?( fd ) V'u < fd )) exp(2j<t>0 )}
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