2.4dB conversion gain from a downconverting mixer with +36dBm IIP3

September 03, 2013 // By Graham Prophet
LTC5551 is a what Linear Technology terms an ultra-high dynamic range RF down-converting mixer for demanding applications. It offers very high linearity of +36 dBm IIP3, (input third-order intercept), and low 9.7 dB noise figure – comparable to the highest IIP3 passive mixers available.

Unlike passive mixers which typically have 7 dB to 9 dB of conversion loss, the LTC5551 boasts 2.4 dB of conversion gain, substantially improving receiver dynamic range. The device also has broad RF frequency range capability, operating from 300 MHz to 3.5 GHz.

Passive mixers require high LO (local oscillator) drive to reach their headline IIP3. The LTC5551 has an integrated LO buffer requiring only 0 dBm drive level, hence external circuitry and costs are minimised. With the elimination of a high power LO signal in the users’ receiver, it substantially reduces a potential source of undesirable radiation, thus simplifying filtering and RF shielding requirements.

LTC5551 ensures robust radio performance with its high 1-dB compression point of +18 dBm. Both the RF and LO inputs have integrated balun transformers, further reducing cost and external components while simplifying the design task. The mixer is powered from a single 3.3V supply with current consumption of 204 mA. If needed, the mixer also has a low power mode controlled via the ISEL pin. In this mode, current consumption drops by 30% to 142 mA, trading off the IIP3 slightly to +29.3 dBm.

The performance of this mixer suits it, Linear says, for a wide range of mission-critical, high performance applications that are exposed to strong interference sources such as multi-carrier GSM, 4G LTE and LTE-Advanced multimode basestations, point-to-point backhauls, military communications, wireless repeaters, public safety radios, VHF/UHF/white-space broadcast receivers, radar and avionics.

The mixer can be shut down with an enable control pin. When disabled, the IC draws a maximum of 100 µA standby current. The device turns on and off in 500 nsec, suitable for burst-mode receivers. It is specified for operation from -40°C to 105°C case temperature. The mixer’s minimum external circuits and its 16-lead, 4 x 4 mm QFN package provide a highly compact solution footprint. The LTC5551 costs $7.25 (1,000)

Linear Technology; www.linear.com/product/LTC5551