Wireless Systems Design

Low-Profile Chip set Suits GSM/EDGE Base-station Transmitter Applications

A high-performance SiGe I/Q modulator and digital RF variable-gain amplifier (VGA) chipset designed by Maxim Integrated Products is aimed at GSM/EDGE basestation transmitter applications.

Together, the MAX2021/MAX2023 I/Q modulators and the MAX2058/MAX2059 VGAs deliver the lowest noise and highest linearity of any competing direct-conversion (zero-IF) transmitter solution, claims the company. When paired with Maxim’s MAX5873 dual DAC and MAX4395 quad amplifier, the MAX2021/MAX2023 I/Q modulators and the MAX2058/MAX2059 VGAs form a digital baseband-to-RF VGA chipset that meets all spectral-mask and noise-floor requirements for single-carrier GSM850/900 and DCS1800/PCS1900 EDGE basestations.

When cascaded together, the complete chipset delivers +15 dBm of output power, +32 dBm of OIP3, and an output-noise level of less than -156 dBc/Hz (at 6 MHz offset). LO leakage (nulled) is less than -40 dBc over the extended -40ºC to +85ºC temperature range. Complete lineup gain control is provided by the SPI-controlled RF digital VGAs. That’s because the two on-chip attenuators support 12 dB of static control, 30 dB of dynamic control, and more than 10 dB of lineup compensation.

The chipset's noise and linearity performance is driven primarily by the company’s MAX2021/MAX2023 zero-IF I/Q modulators. Both modulators boast output-noise-density levels of -174 dBm/Hz that match the theoretical thermal limit.

Each of the MAX2058/MAX2059 RF digital VGAs yields 62 dB/56 dB of total adjustment range, +15 dBm of output power, 32.3 dBm/31.8 dBm of OIP3, and a low spurious emission of -39.2 dBc/-39.1 dBc at a 200-kHz offset, respectively.

In addition to the two digital attenuators, the VGAs feature two-stage RF amplifiers, an on-chip SPI decoder, two loopback switches, and a novel loopback mixer. When paired with the company's MAX9491 synthesizer, the loopback mixer can translate the transmit signal frequency up or down, enabling a direct feed into the receiver band. As a result, the the system can be configured for simultaneous, real-time diagnostic monitoring of both the transmitter and receiver chains.

The chipset’s 26- by 27-mm footprint represents a 50% space savings over a comparable circuit functions

The MAX2021/MAX2023 and MAX2058/MAX2059 come in 36-TQFN and 40-TQFN packages, respectively. Prices start at $4.98 (in lots of 1000-plus) for the MAX2021/MAX2023, and $7.96 (also in 1000-plus lots) for the MAX2058/MAX2059. For more information, visit http://www.maxim-ic.com/gsmtx

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