RF Electronics Chapter 5: Frequency Mixers Page 121
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
increasing LO drive level. A higher LO power level increases the power consumption of
the mixer, requires a higher power LO source and dissipates more heat. By comparing
figures 5.17, 5.26 and 5.34, it can be seen that the conversion loss of the single diode
mixer is very poor.
Figure 5.17. Conversion loss of a single diode down-conversion mixer.
The IF spectrum can be determined using the Frequency Domain Power Measurement
shown in figure 5.18. The waveform at the IF port is determined using the harmonic
balance simulator. The spectral components are determined from that waveform.
Figure 5.19 shows the resulting IF spectrum for an input power at the LO port of +6 dBm.
It is possible to select other values or to plot the spectra for a sweep of power values.
Figure 5.18. Frequency domain power measurement.
In figure 5.19, the desired 5 MHz component is -16.6 dBm. Since the RF signal is -5 dBm,
the conversion loss is 11.6 dB. The LO signal at 105 MHz is 7 dBm and the LO signal at
the IF port is -30.26 dB. The LO to IF isolation is thus 37.26 dB. The RF signal at 100
MHz signal is -5 dBm and the RF signal appearing at the IF port is -28.66 dBm. The RF
to IF isolation is thus 23.66 dB. Comparing this with figure 5.8(left) for the multiplier,
shows that the single diode mixer produces a large number of unwanted components.
Since the IF bandwidth is 20 MHz, it is not possible to filter out the unwanted 10 MHz,
RF Electronics: Design and Simulation
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