Ultra-wideband 3 GHz to 20 GHz mixer with integrated LO buffer

Ultra-wideband 3 GHz to 20 GHz mixer with integrated LO buffer

New Products |
By Jean-Pierre Joosting

The mixer can be used either as an up- or downconverter. The device integrates an LO buffer requiring only 0 dBm input drive, effectively eliminating an external high power LO amplifier circuit. Moreover, the LTC5553 integrates wideband balun transformers on chip. So all ports operate single-ended, 50Ω matched over their respective specified frequency range. In addition, the mixer has excellent port-to-port isolation, offering –32 dBm LO to RF leakage at 17 GHz, thus easing external filtering requirements. All of these features result in minimum external components, simplified design and a very small solution size.

The LTC5553’s extremely wide bandwidth and performance is ideal for a wide range of applications including 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.

The LTC5553 is offered in a tiny 12-lead, 3mm x 2mm plastic QFN package. The device is rated for operation from –40°C to 105°C case temperature to support extended environmental operating temperature. The mixer 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 be driven 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.

Next – improving microwave mixer technology

Most microwave 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. In contrast, the LTC5553 is constructed using a very high frequency advanced SiGe BiCMOS process. Therefore high level of integration is a huge advantage by packing an on-chip LO buffer amplifier and ultra-wideband microwave balun transformers. The monolithic die is flipped and soldered onto a tiny 3-mm x 2-mm lead-framed, plastic surface mount package. Bond wires are eliminated, greatly enhancing the device’s microwave frequency performance without introducing bond wire inductances. Its inherently small package, along with minimum external circuitry, makes for a significantly smaller size. The small footprint enables the possibility of packing in massively parallel active antenna arrays implementation of beam-steering phased-array architecture.

Linearity performance also improved with the new mixer. The LTC5553 offers 21.5 dBm typical IIP3 at 17 GHz, a solid 4-5 dB higher IIP3 than the traditional microwave type mixers.

Additionally, by integrating the wideband LO buffer amplifier in the LTC5553, it greatly simplifies the task for the designers. Since the LO input requires only a 0 dBm drive, it effectively eliminates having an external high power LO amplifier. Not only does it save costs, it also eliminates having a +10 dBm to +17 dBm 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. Thus more filters may be required to keep signal corruptions under control, as well as extra shielding hardware may be necessary to contain the radiation.

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