A high-linearity direct-conversion in-phase/quadrature (I/Q) demodulator is striving to reduce the cost of third-generation (3G) and WiMAX base-station receivers. Dubbed the LT5575, it boasts an operating-frequency range from 800 MHz to 2.7 GHz. This frequency range covers all of the cellular and 3G infrastructure, WiMAX, and RF-identification (RFID) bands. The LT5575 offers an input-third-order-intercept point (IIP3) of +28 dBm and an input-second-order-intercept point (IIP2) of +54.1 dBm at 900 MHz. At 1.9 GHz, it provides an IIP3 of +22.6 dBm and IIP2 of +60 dBm. In addition, the device has a conversion gain of 3 dB. When it is combined with a double-sideband (DSB) noise figure of 12.7 dB, that conversion gain produces superior receiver dynamic range. The device's I and Q outputs have typical amplitude and phase matching of 0.04 dB and 0.6 deg., respectively. In addition, the LT5575 integrates two matched, high-linearity mixers. These are driven in quadrature by a low-noise, buffered local oscillator with an on-chip, precision 0 and 90 deg. phase shifter. The mixers produce accurate I and Q demodulated outputs that can support a baseband bandwidth from DC up to 490 MHz. Both the RF and the LO inputs have integrated on-chip transformers that enable 50-Ω broadband matching and single-ended operation. The LT5575 operates from a single 5-V supply. It draws a quiescent supply current of 132 mA. The device comes in a 16-lead, 4 X 4-mm QFN package. P&A: $7.75 each in 1000-piece quantities; available now.
Linear Technology Corp., 1630 McCarthy Blvd., Milpitas, CA 95035-7417; (408) 432-1900, FAX: (408) 434-0507, Internet: www.linear.com
