Harmonic Mixing with the HSCH-5500 Series Dual Diode - App Note

The difficulty of generating local oscillator power at higher frequencies has stimulated interest in conversion with subharmonic local oscillators for nearly forty years [1]. Earlier designs were inefficient because so much of the signal power was used to generate the unwanted fundamental mixing product. Harmonic mixing conversion loss was 3 to 5 dB worse than fundamental mixing conversion loss. Within the past decade this problem was solved with an improved circuit which does not allow fundamental mixing, the antiparallel pair [2, 3]. This circuit has the additional advantage of suppressing local oscillator noise and all even order mixing products. However, the degree of suppression of these unwanted products is related to the matching of the diode pair.

Adjacent diodes on a wafer are nearly identical electrically. However, it is difficult to separate diodes while maintaining knowledge of each diode's position on the wafer. This problem is solved by making the diodes as monolithic pairs with a cathode-anode connection that remains when the wafer is separated. Figure 1 shows a Schottky pair with the capacitance of each diode less than 0.10 pF. Capacitance difference is less than 0.02 pF. Figure 2 shows the diode dimensions. This monolithic pair is available in the medium barrier version as HSCH-5511 as well as the low barrier HSCH-5531.