3.3V mixer downconverts RF with good linearity
By Paul Rako, Technical Editor -- EDN, October 28, 2009
Linear Technology Corp’s new LTC5541 downconverting mixer operates at frequencies of 1.3 to 2.3 GHz, and the company plans to later introduce pin-compatible parts that will operate at 0.6 to 4 GHz. The device operates from a 3.3V supply and consumes 630 mW of power during operation and 500 μA in shutdown mode. You can power the IF (intermediate-frequency) amplifier with 5V to improve 1-dB gain compression, and using local oscillator with a frequency of 1.4 to 2 GHz improves performance. The mixer can switch between two local-oscillator inputs, which function with a drive level of 0 dBm (decibels referenced to milliwatts); both stay at 50Ω impedance during shutdown so that PLL (phase-locked-loop) circuits remain locked. The part achieves an IIP3 (input third-order-intercept point) of 26 dBm, a noise figure of 9.6 dB at 1.95 GHz, and a conversion gain of 7.8 dB at 1.95 GHz.
The mixer finds use in both the main- and predistortion-receiver paths. Typical applications include LTE (long-term evolution) and CDMA (code-division-multiple-access) wireless base stations and WiMax (worldwide-interoperability-for-microwave-access), WCDMA (wideband-CDMA), UMTS (universal-mobile-telecommunications-system), and EDGE (enhanced-data-rates-for-global-system-for-mobile-communication evolution) systems. You can also use it for backhaul-wireless service between base stations and public-safety, and military-communications systems.
The LTC5541 operates at a −40 to +85°C junction temperature; comes in a 5×5-mm, 20-pin QFN package; and sells for $6.50 (1000). Production has begun.
