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Linear transmit mixer streamlines basestation design

Posted: 02 Aug 2004 ?? ?Print Version ?Bookmark and Share

Keywords:rf active transmit mixer? linear technology? lt5521?

Linear Technology disclosed that its new RF active transmit mixer provides linearity and signal-to-noise performance matching that of passive mixers, allowing designers to build 3G cellular basestations that are more compact and at substantially reduced cost.

According to the company, the LT5521 streamlines basestation design by resolving the high LO (Local Oscillator) drive level, poor LO suppression and low conversion gain issues common to passive solutions. In addition to applications in wideband CDMA, UMTS, GSM and PHS basestation transmitters, the device's low distortion is suitable for cable downlink infrastructure.

The RF active transmit mixer incorporates a differential input and output architecture, supporting superior linearity over the 10MHz to 3.7GHz operating frequency range. It also provides flexible operation in either an upconverting or downconverting application. As a transmit (upconverting) mixer, the input third-order intercept (IIP3) is 24.2dBm at 1,950MHz, and the Noise Figure (NF) measures 12.5dB.

Unlike passive mixers, which require a high LO drive level of as much as 17dBm, the LT5521 needs only a modest -5dBm LO signal. This saves one or two stages of external LO amplifier, resulting in a more compact solution size and lower cost. Additionally, the product offers reduced LO leakage from the LO to other input and output ports. Linear Tech said that this solves a major design headache by removing undesirable LO signal from the transmit path. Also, unlike passive mixers, which typically have high conversion loss in the 6dB to 10dB range, the new mixer has a 0.5dB loss.

The LT5521 operates from either a single 5V or 3.3V supply, and comes in a 16-pin 4-by-4mm surface-mount QFP package. In 1,000-piece quantities, the device is priced at $4.95.

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