RF/IF Chips Simplify Next-Gen Basestation Designs

As carriers upgrade their basestations to add subscriber capacity and implement new data services, many are considering new designs that also will support 3G and future 4G features. These wideband systems using WCDMA, and eventually orthogonal frequency-division multiplexing (OFDM), require a whole new approach to basestation design.

One of the more promising approaches uses direct-conversion transceivers. Because the receivers convert directly to baseband and the transmitters upconvert directly to RF, the RF signal chains are smaller and simpler. They also ease the data-conversion problems associated with high intermediate frequencies (IFs). Skyworks Solutions' latest products make this approach a breeze.

Skyworks' SKY73010 is a direct quadrature modulator for executing a direct conversion transmitter (see the figure). It accepts inputs from the digital-to-analog converters (DACs) driven by the baseband DSP. Also, it produces I and Q signals that are summed into a single output at the final frequency without further upconversion.

The input frequency ranges from dc to over 250 MHz. The RF output and local-oscillator (LO) input range is 300 to 2500 MHz, making the chip useful from the original 800- to 900-MHz and 1800- to 1900-MHz PCS bands up to the newer 2100-MHz 3G band.

One of the chip's exceptional features is its ­155-dBm/Hz broadband noise floor. Also, its carrier suppression exceeds 35 dBc, while its sideband suppression tops 45 dBc. Linearity is superior to other available devices, suiting it for wideband CDMA or OFDM signals.

Made with silicon-germanium biCMOS. the SKY73010 comes in a 16-pin, 4- by 4-mm RF land and grid array (RFLGA) surface-mount package. Available now, it's priced at $5.25 in 10,000-unit quantities.

The SKY73010 is just one of an entire line of RF/IF chips designed exclusively for basestation design. The accompanying receiver chip, the SKY73009 direct quadrature demodulator, targets the 400- to 3000-MHz range. Available phase-locked-loop synthesizers round out the complete basestation transceiver.