Ultra-wideband mixer integrates LO buffer for high dynamic range

Jon Lawson

Aimed at applications such as 5G microwave backhaul, broadband wireless services, satellite broadband radios, radar systems. Nick Flaherty reports

Linear Technology has developed an RF mixer with an integrated local oscillator that fits into a tiny 3 x 2mm package.

Most mixers are built using GaAs FETs or diodes in hybrid modules.

While this technology provides very high frequency capability, however, integration is more difficult to attain.

The LTC5553 is constructed using a very high frequency SiGe BiCMOS process which allows the LO buffer amplifier and ultra-wideband microwave balun transformers to be integrated into the die.

This in turn eliminates the bond wires, enhancing the device’s microwave frequency performance without introducing additional inductances and enabling massively parallel active antenna arrays implementation of beam-steering phased-array architecture.

The double balanced LTC5553 offers a higher linearity of 21.5dBm at 17GHz, 4-5dB higher than other microwave mixers, across the 3 to 20GHz range.

As the LO input requires only a 0dBm drive, it effectively eliminates having an external high power LO amplifier.

Not only does it save costs, it also eliminates having a +10dBm to +17dBm power signal in the system.

At frequencies 10’s of GHz, such high power signal is potentially a major source of LO radiation that can couple to the RF or the IF ports, as well as other sensitive radio circuits. This can require additional filters to minimise signal interference as well as extra shielding.

This gives the mixer port-to-port isolation of –32dBm LO to RF leakage at 17GHz, again reducing the need for external filters.

The mixer is aimed at applications such as 5G microwave backhaul, broadband wireless services, satellite broadband radios, radar systems, active antenna arrays, X and Ku band transceivers, test equipment, spectrum analysis and satellite communications.

It is rated for operation from –40°C to 105°C case temperature to support extended environmental and is powered from a single 3.3V supply, drawing a quiescent supply current of 132mA.

Additionally, the LTC5553 can be shut down via an enable pin.

When deactivated, the device draws only 100μA maximum standby current.

The enable pin can bedriven directly to turn the device on and off rapidly in less than 0.2μs, supporting time-division duplex (TDD) or burst mode type transmitters and receivers.