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Linear has the Solution
The nascent exponential growth of smart phones, iPADs, tablet PC, notebooks and netbooks contributed to an insatiable demand for wireless networks' data speed and capacity. Wireless service providers everywhere are scrambling to accelerate their schedule of deployment of 4th generation wireless technology, LTE, which promises many times increase in data rate. To help reduce their cost of deployment, the base station industry is trending toward building few platforms - ultimately to a single platform - that can be field-configured for different frequency bands and different standards for different markets and countries. In effect, the goal is to develop a flexible, software configurable base station that can cover all the frequency bands as well as seamlessly communicate with all cellular standards including LTE, W-CDMA, UMTS, CDMA and GSM. Doing so has enormously positive financial impacts as it provides efficient use of the equipment manufacturers' design resources and reuse of technology, hence improving their cost structure
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Linear Technology announces the LTC5585, an ultrawide bandwidth direct conversion I/Q demodulator with outstanding linearity performance (IIP3 = 25.7dBm and IIP2 = 60dBm at 1.95GHz). The device is capable of baseband output demodulation bandwidth of over 530MHz, which can support new generation wideband LTE multimode receivers' and digital pre-distortion (DPD) receivers' bandwidth requirements. The I/Q demodulator operates over a wide frequency range from 700MHz to 3GHz, covering virtually all cellular base station frequency bands. Unique to this device are two built-in calibration features. One is advanced circuitry that enables the system designer to optimize the receiver's IIP2 performance, increasing from a nominal 60dBm to an unprecedented 80dBm or higher. The other is on-chip circuitry to null out the DC offset voltages at the I and Q outputs. Both serve to enhance receiver performance. Moreover, the LTC5585 delivers excellent P1dB of 16dBm.
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To further enhance its use in direct conversion receiver applications, the LTC5585 offers very low I/Q amplitude and phase mismatch. The amplitude mismatch is typically 0.05dB, while the phase error is typically 0.7 degree, both measured at 1.95GHz. This combination produces a receiver image rejection capability of 43dB. Because of its very wide bandwidth capability, the LTC5585 is especially well suited for multimode LTE, W-CDMA and TD-SCDMA base stations DPD receivers as well as for main receiver applications. Particularly for DPD, these latest generation base stations are pushing demodulation bandwidth of over 300MHz. The LTC5585 can be easily configured to meet these bandwidth challenges. Beyond wireless infrastructure applications, the LTC5585 is ideal for applications in military receivers, broadband communications, point-to-point microwave data links, image reject receivers and long-range RFID readers. The LTC5585 has an on-chip RF transformer to reduce external components, providing a highly compact solution with its 24-lead 4mm x 4mm QFN package. The device is specified for case operating temperature from -40°C to 105°C. The LTC5585 is powered from a single 5V supply, drawing a total supply current of 200mA. The device provides a digital input to enable or disable the chip. When disabled, the IC draws typically 11?A of leakage current.
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Common DPD receiver employed is that of a heterodyne architecture which down converts the RF signal to an IF frequency. It is then filtered and digitized. But a 300MHz bandwidth signal riding on an IF frequency requires an exceedingly high speed A/D converter pushing sampling speeds over 500Msps, which is costly and performance difficult to attain. Hence a wideband direct-conversion I/Q demodulator like the LTC5585 offers an attractive alternative solution to this problem. Such a device can directly down convert the RF signal to baseband or a very low IF frequency. At the baseband, the 300MHz RF signal is now split into two 150MHz wide I (In-phase) and Q (Quadrature-phased) signals. With this reduced bandwidth, achieving better than 1/2dB gain flatness is more manageable. The real compelling benefit is that the baseband signal can now be easily digitized with a 300Msps A/D converter - a commonly available and potentially cost effective solution - albeit two channels are required. Conclusion: the LTC5585 offers a potentially cost-effective, compelling alternative to wideband DPD and main receivers for the emerging 4G infrastructure and other high performance wireless applications. The demodulator's fast turn-on time of 200ns and turn-off time of 800ns enables it to be used in burst mode receivers. Production quantities are now immediately available. For more information, visit www.linear.com/product/LTC5585
