Frequencies can be translated in many ways for signal processing, but frequency mixers tuned with local oscillators (LOs) may still be one of the most trusted methods for conversion, and the LTC5553 double-balanced mixer from Linear Technology (recently acquired by Analog Devices) offers one of the widest bandwidths of any mixer in one of the smallest packages. With an RF range of 3 to 20 GHz and on-board LO amplifier, the integrated-circuit (IC) mixer is supplied in a tiny surface-mount QFN package measuring just 3 x 2 mm. It can be used for frequency upconversion or downconversion, working with an LO frequency range of 1 to 20 GHz and an intermediate-frequency (IF) range of 0.5 to 9.0 GHz.
The LTC5553 has integrated wideband baluns that result in RF, LO, and IF ports matched to 50 Ω and ready for interconnections in many application circuits. The integration of an LO amplifier eliminated the need for external amplifier and matching circuitry when connecting an LO source. The mixer delivers the wideband performance suitable for a wide range of applications, including 4G and 5G wireless access, point-to-point microwave radios, radar systems, satellite modems, and test equipment. With its fast times of turning on (typically 0.2 μs) and off (typically 0.1 μs), the double-balanced mixer is also a good fit for time-division-duplex (TDD) radio systems.
The integrated LO amplifier allows the use of typical LO power level of 0 dBm without compromise in conversion-loss performance. The conversion loss is low across the full bandwidth. For a downconversion application with IF of 1890 MHz, the conversion loss is typically 8.2 dB for an RF of 4 GHz, 9.0 dB for an RF of 10 GHz, 11.3 dB for an RF of 14 GHz, and 11.6 dB for an RF of 17 GHz. For an upconversion application with the same IF, the conversion loss is essentially the same, typically 8.3 dB for an RF of 4 GHz, 9.3 dB for an RF of 10 GHz, 11.9 dB for an RF of 14 GHz, and 11.5 dB for an RF of 17 GHz. For applications that must operate within a wide temperature range, the conversion loss remains fairly constant with temperature. When tested with an RF input of 9.8 GHz, the conversion loss as a function of temperature was 0.006 dB/ºC from -40 to +105ºC.
In spite of the small size, the mixer features well isolated ports, with typical RF-to-LO isolation of better than 40 dB and typical RF-to-IF isolation of better than 32 dB, with both characteristics specified across the full RF frequency range. The tiny mixer also keeps LO signals where they belong, with typical LO-to-RF leakage of -32 dBm at 17 GHz. On the high side of the dynamic range, the mixer achieves input third-order intercept point (IIP3) of +23.9 dBm at 14 GHz and +21.5 dBm at 17 GHz. The single-sideband (SSB) noise figure is typically 10.9 dB at 10 GHz and 12.8 dB at 15.7 GHz.
The broadband double-balanced mixer is housed in a12-lead plastic QFN package with each port connection surrounded on either side by ground lead connections. It draws just 132 mA current from a +3.3 V dc supply and is rated for operating temperatures from -40 to +105ºC. Although it is designed to perform well with low LO power, it can handle LO levels as high as +10 dBm and RF and IF input power levels as high as +20 dBm. One mixer may not do everything, but this one does come close.
Analog Devices Inc., 1630 McCarthy Blvd., Milpitas, CA 95035-7417; (408) 432-1900, www.linear.com.
