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Motivated by customer feedback to improve the bandwidth and linearity of I/Q demodulators, Linear Technology Corp. (LTC) has combined its second-generation SiGe bipolar process with improvements in frequency range of on-chip transformers and phase shifter. As a result, the supplier’s latest I/Q demodulator LT5575 offers high linearity and broadband for direct conversion in base station receivers and RFID readers.

Consequently, the LT5575's extended operating frequency range from 800 MHz to 2.7 GHz covers all of the cellular and 3G infrastructure, WiMAX and RFID bands with a single part. Its capability to convert from RF directly to baseband at DC or low frequency results in simplified receiver designs, reduced component count and use of lower cost, low frequency components.

Plus, it offers an outstanding IIP3 of 28 dBm and IIP2 of 54.1dBm at 900 MHz, and an IIP3 of 22.6dBm and IIP2 of 60 dBm at 1.9 GHz. Moreover, the device has a conversion gain of 3 dB, which when combined with a DSB noise figure of 12.7 dB produces excellent receiver dynamic range. The device's I and Q outputs have typical amplitude and phase matching of 0.04 dB and 0.6 degree, respectively, providing demodulation accuracy.

Hence, the demodulator is capable of supporting multiband base stations covering both the 850 MHz GSM/EDGE bands and the 1.9 GHz/2.1 GHz 3G wireless services (including CDMA2000, WCDMA, UMTS, and TD-SCDMA). It is suitable for single carrier micro- and pico-base stations, where low cost architectures are key. Furthermore, its performance makes it suited for 2.6 GHz WiMAX base stations, and as an IF demodulator in a microwave radio link or satellite receiver. Over and above, the unit’s high 13.2 dBm P1dB (1dB compression point) performance at 900 MHz lends it to high-performance RFID readers.

The LT5575 integrates two matched, high linearity mixers. These are driven in-quadrature by a low-noise, buffered local oscillator (LO) with an on-chip precision 0° and 90° phase shifter. The mixers produce accurate I and Q demodulated outputs capable of supporting a baseband bandwidth from DC up to 490 MHz. Both the RF and the LO inputs have integrated on-chip transformers that enable 50 Ohm broadband matching and single-ended operation. This simplifies the design and reduces costs.

The LT5575 operates from a single 5 V supply, drawing a quiescent supply current of 132 mA. The device comes in a 16-lead 4mm x 4mm QFN package.