RF Electronics Chapter 5: Frequency Mixers Page 123
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 5.21. IF voltage for a single diode mixer as a down-converter.
Figure 5.21 shows the resulting IF voltage of a single diode mixer, notice with the 2
nd
order filters used in the diplexer, there is still significant RF voltaget components present
in the IF signal. A higher order filter will improve the isolation, but will not improve the
performance sufficiently to justify the additional cost. For the frequencies used, the output
spectra and conversion loss will be the same if higher order diplexer filters are used. As
can be seen from figure 5.21, the single diode mixer has a significant DC voltaget
component, which changes with LO drive level.
To operate the frequency mixer as an up-converter, the PORTF element is applied to the
IF port and the signal generated by that port is set to 5 MHz and a power of -5 dBm. The
mixer output is then at the RF port. Figure 5.22 shows the resulting circuit diagram for
the single diode mixer as an up-converter. The same measurements can be performed for
the down-converter.
Figure 5.22. Circuit diagram of a single diode mixer as an up-converter.
RF Electronics: Design and Simulation
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