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Modulator improves wireless transmitter performance

Posted: 06 May 2009 ?? ?Print Version ?Bookmark and Share

Keywords:modulator? transmitter? base station?

From Linear Technology Corp. comes a new low frequency direct conversion quadrature modulator that offers superior linearity performance and low noise to enhance the dynamic range performance of base station transmitters.

The LTC5598 offers +27.7dBm OIP3 (Output 3rd Order Intercept) and +74dBm OIP2 (Output 2nd Order Intercept) performance. In addition, the device has an low noise floor of -160dBm/Hz at a +5dBm output level. Moreover, the LTC5598 provides -50.4dBc image rejection and a carrier leakage of -55dBm. It consumes 20 percent less power compared to its closest competitor. The combination of function and performance enables design of compact, high performance transmitters for wireless infrastructure equipment.

The LTC5598 has outstanding dynamic range performance, from low frequency to above 1GHz, making it ideal for point-to-point broadband microwave links, 450MHz and 700MHz LTE base station transmitters, 800MHz GSM/900MHz Edge base station transmitters, 880MHz CDMA2000 base stations, video and cable broadband modulators, multiband military radios, 900MHz multiprotocol RFID readers and satellite transmitters. It is also uniquely capable of operating down to 5MHz, enabling many very low-frequency applications such as 13.56MHz RFID and contactless readers, telemetry, military communications and medical instrumentation.

The LTC5598 integrates two matched, high linearity double-balanced mixers and a broadband precision quadrature phase-shifter with buffered LO. The phase-shifter maintains an accurate 90 phase relationship between the I and the Q mixers' LO inputs to provide excellent image rejection over a wide frequency range. The I and Q input bandwidth of over 400MHz supports virtually all broadband digital transmission requirements. For ease of use, the two mixer outputs are summed into a single-ended, 50? terminated RF output.

The LTC5598 operates from a single 5V supply. It runs on a quiescent current of 168mA, consuming 20 percent less power than other comparable modulators. The LTC5598 provides a power-down feature with turn-on and turn-off time of 75ns and 10ns, respectively, supporting Time Division Duplex type transmitters. When the chip is disabled with a logic LOW applied to its ENABLE input pin, the device draws a typical shutdown current of 43?A. The LTC5598 comes in a 24-lead, 4mm x 4mm QFN surface mount package. Pricing starts at $5.19 each in 1,000-piece quantities. The LTC5598 is available immediately from stock.

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