New wideband I/Q demodulator improves receiver performance

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.

The LTC5585 also 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 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.

It is powered from a single 5V supply, drawing a total supply current of 200mA and the device provides a digital input to enable or disable the chip. When disabled, the IC draws typically 11μA of leakage current. The demodulator’s fast turn-on time of 200ns and turn-off time of 800ns enables it to be used in burst mode receivers.

Linear Technology

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