hf/rf ZONE Products for the week of November 17, 2003
Linear Technology Corporation Says . . .
LT5522: Active Mixer Enhances Dynamic Range &
Reduces Costs for Wireless & Cable
Linear Technology Corporation introduced the LT5522, a new high performance active downconverting mixer that operates with RF input from 600MHz to 2.7GHz. The device's combination of performance, matched input characteristics, and low external component count simplifies design and reduces costs for high performance cellular base stations, cable headend equipment and fixed wireless access radios.
The LT5522 offers high third-order intercept (IP3) performance, extending system dynamic range and simplifying receiver design. Moreover, the LT5522 RF input has an on-chip transformer that is 50 Ohm matched over a wide frequency range. Both the RF input and the LO (Local Oscillator) ports can be driven differentially or single-ended with minimum external impedance matching components. The LO port requires low drive levels and optimum performance is achieved with an LO input power level of -5 dBm.
The LT5522 has exceptionally low port-to-port feedthrough, thus reducing filtering requirements. The LT5522 draws only 56mA of supply current at 5V, minimizing power supply requirements. The device is available in a small footprint 4mm x 4mm plastic flat package.
The LT5522 is optimized to enhance the performance of wireless infrastructure
applications. Moreover, its exceptional linearity makes it an excellent
building block for cable headend transmitters and receivers, high performance
fixed wireless access radios and satellite receivers.
analogZONE Says . . .
You know that report card everyone gets in school at least once -- even the cleverest of students -- "could do better." It's a downer but a challenge. When analogZONE reviewed Linear's LT5515 and LT5516 direct conversion products in September 2003 we noted that we hoped the company was working on getting the single-ended to differential transformer needed to drive the input on-chip instead of it having to be provided as an external component. A month later a data sheet was put down in front of me at LTC's headquarters for the LT5522 where exactly that had been done. It certainly wasn't my intervention that achieved that -- the design must have been 9 months in the making.
And the LT5522 does not replace the LT5515/5516 as it is not a direct conversion I/Q product, but the technology has been clearly reused and it does show some fairly dramatic improvements in performance that the company has been able to achieve; the kind of learning path that is essentially analog, and so wonderful.
First the LT5522 is a downconverting mixer and instead of having the band split into two, as before, the part operates over the complete range of 600 MHz to 2.7 GHz. The LO input is single-ended with a simple RC network, although differential can still be used, and the drive requirements are still kept remarkably low between 0 dBm and +10 dBm. Conversion gains have been improved by over 0.5 dB at the higher frequencies and there is a nice balance of conversion gain across the whole band. Noise figures have also been improved by over 2 dB. But probably the biggest increase in performance is in the S11 characteristics which results in a delightfully simple input matching network with a series capacitor and shunt inductor alone (3.3 pF and 10 nH.) giving better than 12 dB return loss from 700 MHz to 2.3 GHz, which obviously can be further improved over your bandwidth of choice.
Typical IF outputs will be 140 MHz for cellular/PCS applications with a low-side LO, and 50 MHz to 1.05 GHz for cable applications with a high-side LO. All the numbers look good to very good, with IP3 at 900 MHz equal to +25 dBm (+21.5 dBm at 1.9 GHz), and RF/IO and IO/RF leakage in the -50 dBm ranges. The input 1-dB compression points are 10.8 dBm at 900 MHz and 8.0 dBm at 1.9 GHz. The supply rail is a nominal 5 V with a typical draw of 56 mA.
The LT5522 is extremely serious competition to those vendors already in the downconversion market for cellular and CATV. The wide RF bandwidth of the part also suggests that LTC will start to get inquiries from designers of systems that neither it, or me, would ever have thought of.
The LT5522 is in production in a 4 mm x 4 mm QFN-16 and is priced at $5.20 in 1000-piece lots.