300MHz to 6GHz dual wideband mixer

Louise Smyth

Linear Technology has developed a wideband, high dynamic range dual channel mixer with integrated programmable variable gain IF amplifiers.

The LTC5566 has a very wide, 300MHz to 6GHz input frequency range, specifically optimised and with extensive characterisation at the emerging 3.6GHz and 4.5GHz 5G bands, as well as the established 4G bands.

The mixer also supports bandwidths up to 400MHz to meet the needs of the growing sub-6GHz 5G wireless access equipment.

The device has a dynamic range of +11.5dBm for the Input P1dB and +25.5dBm for Input IP3 (IIP3) at 3.6GHz.

At higher frequencies, up to 5.8GHz, the IIP3 sustains more than +24dBm. An integrated IF amplifier boosts the overall power conversion gain to a maximum of 12dB and the gain of each channel is independently programmed in precise 0.5dB steps via the on-chip SPI bus.

With each channel driving an A/D converter, the fine gain control provides a simple means to balance the gain of the two channels and calibrate to the optimum level with minimal external components.

The LTC5566 is aimed at 5G wireless multichannel RRH (remote radio head) wireless access equipment that requires better performance and wider bandwidths at higher frequencies with more channels in a smaller enclosure.

Other suitable applications include 4G LTE-Advanced, diversity receivers, distributed antenna systems and software-defined radio.

The LTC5566 is built on an active, double-balanced mixer core with no conversion loss and with excellent port-to-port isolation, reducing external RF filtering requirements. Each mixer input includes an integrated wideband balun transformer, allowing a simple single-ended interface.

The SPI or parallel pins allow the mixer inputs can be digitally tuned for optimum return loss over several wide, overlapping frequency bands, ranging from 1.3GHz to 5.3GHz, ensuring flexibility for use in software-defined radio applications without extra external components.

The lower 450MHz, 700MHz and 900MHz bands are also supported by the addition of a single external shunt inductor for proper matching, yielding superb dynamic range performance. Higher frequencies above 5.3GHz, such as 5.8GHz, can be achieved using a simple external matching circuit.

For MIMO receivers, both channels exhibit very low phase shift over the full 15.5dB attenuation range, with 50dB channel-to-channel isolation up to 3.6GHz. At 4.5GHz, the channel isolation is still 40dB.

The LTC5566 operates from a single 3.3V supply. With both channels on, the device draws a nominal supply current of 384mA. Each mixer can be turned on or off independently with separate control lines.

A low power mode is available, ensuring operation at a reduced supply current of 294mA, although with a slight decrease in IP3 performance. The product is rated for –40°C to 105°C case temperature operation and is offered in a 5mm x 5mm 32-lead plastic QFN package.

The LTC5566 is priced starting at $9.45 each in 1,000-piece quantities, and is available immediately in production quantities.