30-MHz to 1.4-Hz wideband I/Q demodulator with IIP2 optimization and DC offset cancellation boosts zero-IF receiver performance

May 15, 2012 // Paul Buckley

Linear Technology has unveiled an ultra-wide bandwidth direct conversion I/Q demodulator with linearity of 31 dBm IIP3 and 70 dBm IIP2.

The LTC5584 offers best-in-class demodulation bandwidth of over 530 MHz, supporting the latest generation of LTE multimode, LTE Advanced receivers, as well as digital predistortion (DPD) receivers. The I/Q demodulator operates over a wide frequency range from 30 MHz to 1.4 GHz, covering a broad range of VHF and UHF radios and the 450 MHz/700 MHz LTE frequency bands.

The LTC5584 has 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 70 dBm to an unprecedented 80 dBm or higher. The other is on-chip circuitry to null out the DC offset voltages at the I and Q outputs. Combined with a 9.9 dB noise figure, these features enhance the dynamic range performance in receivers. Moreover, the device exacts P1dB of 12.6 dBm, along with its 13.6 dB noise figure under a 0 dBm in-band blocker, ensuring robust receiver performance in the presence of interference.

To enhance its flexibility for use in low IF receiver applications, the LTC5584 exhibits very low I/Q amplitude and phase mismatch. The amplitude mismatch is typically 0.02 dB, while the phase error is typically 0.25 degree, both specified at 450 MHz. This combination produces receiver image rejection of 52 dB.

With its wide bandwidth capability, the LTC5584 is ideal for multimode LTE and CDMA DPD receivers as well as other wideband receiver applications. Particularly suited for DPD, these latest generation base stations are pushing demodulation bandwidth of over 300 MHz. The LTC5584 exceeds these bandwidth requirements while delivering better than ±0.5 dB conversion gain flatness. Beyond wireless infrastructure applications, the LTC5584 is ideal for military receivers, broadband communications, point-to-point microwave data links, image-reject receivers and long-range RFID readers.

The LTC5584 is offered in a 24-lead 4mm x 4mm QFN package. The device is specified for case operating temperature from -40 to 105°C. Powered from a single 5 V supply, the LTC5584 draws a total supply current of 200 mA. The device provides a digital input to enable or disable the chip. When disabled, the IC draws 11 µA of leakage current typical. The demodulator’s fast turn-on time of 200 ns and turn-off time of 800 ns enables it to be used in burst-mode receivers.

Availability and Pricing

The LTC5584 is priced starting at $5.65 each in 1,000-piece quantities. Production quantities are available immediately.

More information about the LTC5584 I/Q demodulator at
www.linear.com/product/LTC5584  

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