RF Electronics Chapter 5: Frequency Mixers Page 122
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
15 MHz and 20 MHz components. Comparing figure 5.19 with figure 5.22 for the
balanced mixer, and figure 5.30 for the double balanced mixer, shows that the conversion
loss, the levels of the harmonics and the isolation produced by the single diode mixer are
significantly worse than those of balanced mixers.
Figure 5.19. IF spectrum of a single diode mixer as a down-converter.
If a two-tone RF input signal is used, the single diode mixer has a high level of IM
components. As a result, the single diode mixer requires more stringent RF filtering to
avoid those IM signals being generated by the mixer and appearing in the IF output. The
single diode mixer also requires more stringent IF filtering to remove those unwanted IF
components from the IF signal, to prevent the unwanted signals from affecting the
demodulated output from the receiver. Most AM radios use single diode mixers and this
is one reason why their performance is poor compared to FM radios.
Figure 5.20. Vtime measurement setting.
The voltage and current time waveforms can also be determined, using the Vtime and
Itime measurements. The measurements can be done at a single LO power level or at a
range of levels as is done by selecting plot all traces instead of the 0 dBm level in the
Port_2 entry of the Vtime measurement window shown in figure 5.20. Alternately, as has
been done in this project, a limited power sweep can be obtained by performing multiple
single level measurements as shown in figure 5.21.
RF Electronics: Design and Simulation
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