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RF Electronics Chapter 5: Frequency Mixers Page 120 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Figure 5.16. Setting the number of harmonics used in Harmonic Balance analysis. The conversion gain or loss is the most important mixer parameter. When determining the conversion loss of a mixer, it is important to include many harmonics and IM products, say up to the 7 th or 9 th order in the Harmonic Balance (HB) analysis, as shown in figure 5.15. The number of harmonics can be set using Tools Circuit Options. Even though most of these IM products will fall outside the frequency range of interest, there will still be some falling inside the required bandwidth and will this affect the accuracy of the results produced by the simulation. If in doubt, simply increase the order of the harmonics and IM to be analysed and note any changes in the simulated results. As the speed of computers and the efficiency of the Harmonic Balance calculations increases, there is less cost in erring on the side of calculating an excess of harmonic and IM components. For the figures in this chapter, the Harmonic Balance settings use 9 harmonics for tone 1, tone 2 and tone 3 are used for the HB analysis. Different spectra result, when these values or the default values are used and when APLAC HB or Harmonic Balance (legacy) are used and when the harmonic order is limited to 9 orders or is not limited. Those changes can easily be observed and only effect small IM amplitudes. The current edition of this book uses the APLAC HB simulator, since the Harmonic Balance simulator that was used in the 2013 edition is now a legacy product. The conversion loss of the mixer can be determined as the LO power level is varied, by setting the relevant parameters of the PORT_PS1 element to provide a power level sweep at the LO port. The sum or difference frequency that is analysed for determining the conversion loss is set by the parameters for the Large Signal S parameter (LSSnm) measurement shown in figure 5.15. The conversion loss is determined as the ratio of the power levels at the specified frequencies of port 1 as input and port 3 as output. For a realistic determination of performance of the frequency mixer, a LO frequency of 105 MHz (as set by the project frequency setting in figure 5.15 and an RF frequency of 100 MHz with a level of -5 dBm (as set by PORTF) is chosen. The project frequency is set as a single frequency for speed of simulation. If a range of frequencies is specified, then one or all of these can be used for the conversion loss or spectral output calculations. It is thus possible to determine the conversion loss for a range of LO frequencies as well. For a LO input at 105 MHz and an RF input at 100 MHz, the desired IF output is at 5 MHz. The appropriate harmonic index combinations are selected such that the input is at 100 MHz and the output is at 5 MHz, as indicated in figure 5.15. MWO automatically calculates the relevant frequency as the harmonic indices are changed. Figure 5.17 shows the resulting conversion loss as a function of LO power level for the single diode mixer of figure 5.13. Note that the conversion loss decreases with an RF Electronics: Design and Simulation 120 www.cadence.com/go/awr

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