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RF Electronics Chapter 5: Frequency Mixers Page 111 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Note Cadence AWR DE calculates the conversion gain. As a result, it is more appropriate to use a consistent term conversion gain in the plots and have negative dB values to indicate the loss. The term conversion loss is however used more frequently in literature. To use "Conversion Loss" would require the minus signs to be removed from the Cadence AWR DE generated plots, which is not easy to do. Similarly the term Insertion Gain and Return Gain are used in plots, with negative dB values indicating when the plotted variables have a loss. Isolation In practice it is desirable to have isolation between the LO, RF and IF ports of the mixer. Typical double balanced mixers have more than 30 dB isolation [1, 2] between all ports. Single diode mixers have virtually no isolation between ports. Since single diode mixers are used in TV receivers, the LO signal is coupled to the antenna, which radiates the LO signal. In countries where TV licences are required, the "detector vans" look for the LO radiation and match the radiation coming from a house with any licence fee payment. One can also do a good survey to find out what TV channel people are watching by simply driving around a street with a spectrum analyser and noting the LO frequencies. For a balanced mixer, the isolation is directly related to the match between the diodes used. As a result, many manufacturers sell matched sets of diodes, especially for use in mixers. In many cases two or 4 diodes come as one package. Compression Point For an ideal down-conversion mixer the IF output produced should be directly proportional to the RF input signal. However as the RF input approaches about 10 dB below the LO power. The IF output starts to saturate and the conversion loss starts to increase, as is shown in figure 5.3. Most manufacturers of frequency mixers specify the 1 dB compression point for their mixers [1, 2]. The 1 dB compression point is typically 6 dB below the LO level for mixers up to +23 dBm LO power. Since the 1 dB compression point is related to the LO drive, a higher LO level results in a higher 1 dB compression point and as a result a bigger dynamic range of the mixer. Figure 5.3. 1 dB Compression Point of a mixer. RF Electronics: Design and Simulation 111 www.cadence.com/go/awr