Femtocells are essentially miniature base stations used to enhance cell phone coverage within a home or small office. 3G UMTS femtocells are especially useful in that they support the full 3G capability of the latest smartphones. Providing a 3G femto base station in the form factor of a Wi-Fi access point at an attractive price point, while maintaining base station-like performance, is a real challenge.

ADI has created a demonstration platform consisting of the ADF4602 transceiver, AD9863 mixed-signal front end, ADL5320 and ADL5542 amplifiers, and ADL5501 RF power detector—all in a small two square inch area. Switches, filters, diplexers, power management circuitry, etc. are also included on the demo platform for ease of use; the baseband processor is not included. The circuit shown was developed to support cellular bands 1 and 2. The devices used are fully capable of supporting bands 1 through 6 and 8 through 10. Low power consumption, excellent EVM, ACPR, and sensitivity, along with wide power control range, are additional key features.

Integrated Transceiver Enables Pico- and Microcell Base Stations

The AD9356 and AD9357 provide dual receive, dual transmit transceiver solutions in a single IC. They combine the RF front end with mixed-signal baseband conversion, enabling an easy to use digital interface to the baseband ASIC or FPGA. The devices operate in the 2.3 GHz to 2.7 GHz (AD9356) and 3.3 GHz to 3.8 GHz (AD9357) range; support channel bandwidths of 3.5 MHz, 4.375 MHz, 5 MHz, 7 MHz, 8.75 MHz, and 10 MHz; and can be used for WiMAX and some LTE applications. The direct conversion receiver delivers a stateof- the-art noise figure of 3.5 dB and linearity, while requiring no external components with the exception of a balun. The devices use 12-bit ADCs, which provide the transceiver with more instantaneous dynamic range. Equally as important, a very advanced automatic gain control (AGC) algorithm has been implemented inside the transceiver. The flexible implementation within the AD9356/AD9357 allows for the use of the AGC in autonomous mode or for control in manual mode using real-time signals from the transceiver so that the system integrator can have more control of the system gain. It is with the combination of AGC and high dynamic range ADCs that the transceiver can resolve the near/far problem without the cost of a high performance, high power discrete solution.

Beyond the receiver, the AD9356/AD9357 offer significant improvement in transmit noise floor. In previous generations of integrated transceivers, like the AD9354 and AD9355, the external power amplifier (PA) power was limited to 33 dBm and 27 dBm, respectively, while still meeting the FCC and ETSI spectral mask requirements. The new AD9356 RF transceiver, which operates from 2.3 GHz to 2.7 GHz, is able to achieve –130 dBc/Hz at 8 MHz offset from the carrier and can support up to 40 dBm per transmitter at the antenna port. Exceptional noise performance at this close an offset frequency is essential, as this cannot be filtered externally. The AD9357, which operates from 3.3 GHz to 3.8 GHz, is able to achieve approximately –144 dBc/Hz at 70 MHz offset and can support an external PA up to 33 dBm per transmitter and still comply with the ETSI requirements. In order to support higher PA power output, a simple low cost external low-pass filter can be added. Supporting this higher power PA with integrated transceivers will allow system integrators the ability to extend the range of their systems to enhance coverage, while maintaining low cost deployments.

The AD9356/AD9357 are packaged in a 10 mm × 10 mm, 144-ball CSP_BGA and operate over a temperature range of –40°C to +85°C.

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