RF Electronics Chapter 5: Frequency Mixers Page 126
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
the mixer is then very insensitive to AM noise of the LO. This is an important advantage
of the balanced mixer over the single diode mixer, or even the ideal multiplier of figure
5.7 or the Frater-Gilbert Cell mixer shown in figure 5.76 – 5.87 later in this chapter.
Figure
5.25. Circuit diagram of a balanced mixer.
Figure 5.26. Conversion gain of a balanced diode mixer.
Figure 5.27 shows the IF spectrum of the balanced mixer. As expected from the equation
5.11, many of the unwanted spectral components have significantly reduced amplitudes
compared with the single diode mixer. The difference in amplitude of the 5 MHz and 205
MHz components is due to the low pass filter at the IF port in figure 5.25. A higher order
filter will attenuate the components above 20 MHz more. Figure 5.27 shows that the level
of unwanted components above 80 MHz for the reflectionless filter are slightly higher,
since the Butterworth Low pass filter has a higher attenuation at those frequencies than
the reflectionless filter. Table 5.1 shows how each component in figure 5.27, relates to
the 105 MHz LO and the 100 MHz RF frequencies. The third harmonic of the desired IF
signal, at 15 MHz, is caused by the mixing process and is about 45 dB below the desired
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