The need for higher mobile data throughput is forcing some significant changes in wireless infrastructure equipment. New basestation radios not only must handle higher data rates, but also accommodate multiple 2G/3G/4G standards, consume less power, and fit into smaller spaces.
Those requirements are in conflict with the need to use multiple-input multiple-output (MIMO), which is responsible for producing the desired data rate gains. Yet most of this is accomplished with the emerging remote radio heads (RRHs) mounted on the tower with the antennas. The key circuitry for MIMO in the receivers in this new configuration is the mixer.
Linear Technology’s LTC559x dual high-dynamic-range downconverting mixers are helping designers to implement the new architecture. The primary applications are wideband MIMO receivers, RRHs, and diversity receivers. Four devices cover the 600-MHz to 4.5-GHz range. The LTC5590 covers 600 MHz to 1.7 GHz, the LTC5591 covers 1.3 to 2.3 GHz, the LTC5592 covers 1.6 to 2.7 GHz, and the LTC5593 covers 2.3 to 4.5 GHz. The LTC5591 is available now with the other devices coming in July, August, and September.
All the mixers are made with bipolar complementary metal-oxide semiconductor (biCMOS) silicon germanium (SiGe) and come in a 24-lead, 5- by 5-mm plastic quad flat no-lead (QFN) package (see the figure). Also, all of the mixers have identical pinouts, permitting designers to share printed-circuit board (PCB) layouts across multiple platforms operating in different frequency bands. The mixers require 3.3 V at 380 mA, about 1.25 W as well.
The LTC559x dual mixers feature a separate IF amplifier and local oscillator (LO) buffer per channel. On-chip balun transformers provide single-ended drive on all inputs each at a 50-Ω impedance. The LO input is shared by the two mixers and requires 0-dBm input power. Each mixer can be independently shut down when it isn’t needed, saving power.
As for circuit specifications, the available LTC5591 is a good example. Its conversion gain of 8.5 dB makes it possible to use superior selectivity but lossy IF filters. Its third-order intercept point (IIP3) is 26.5 dBm at 1950 MHz. The noise figure (NF) at that frequency is 9.9 dB. The NF is 15.5 dB with 5 dBm of blocking. The channel-to-channel isolation is a high 47 dB.
Samples and production quantities of the LTC5591 are available now for $9.50 in 1000-piece quantities.
Linear Technology Corp.