Maxim Chipset Enables Direct-Conversion Transmitter For GSM/EDGE Base Stations
The pressure of reducing costs while maintaining or even improving performance continues for wireless infrastructure applications. With the introduction of the MAX2021/MAX2023 and MAX2058/MAX2059 series of high-performance I/Q modulators and RF digital VGAs, Maxim claims these new components form the industry's first and only digital baseband-to-RF VGA chipset that meets all spectral-mask and noise-floor requirements for single-carrier GSM850/900 and DCS1800/PCS1900 EDGE base stations.
When cascaded together, the complete chipset delivers +15dBm of output power, +32dBm of OIP3, and an output-noise level of < -156dBc/Hz (at 6MHz offset). LO leakage (nulled) is also rated at < -40dBc over the extended -40 degrees Celsius to +85 degrees Celsius temperature range. Complete lineup gain control is provided by the SPI-controlled RF digital VGAs, as the two on-chip attenuators support 12dB of static control, 30dB of dynamic control, and > 10dB of lineup compensation.
The chipset's noise and linearity performance is driven primarily by the new MAX2021/MAX2023 zero-IF I/Q modulators. Both modulators feature output-noise-density levels of -174dBm/Hz that match the theoretical thermal limit. In addition, the MAX2021/MAX2023 yield OIP2, OIP3, and OP1dB levels of up to 57.9dBm/61dBm, 22.3dBm/23.5dBm, and 16.7dBm/14.3dBm, respectively. When you couple the noise performance with the raw P1dB values, the gross dynamic range is greater than 190.7dB/188.3dB-a 16.7dB/14.3dB performance leap over the closest competitors. These performance improvements directly enhance a BTS transmitter's spectral mask performance, and allow the MAX2021/MAX2023 to exceed the strict spectral-mask requirements for GSM/EDGE BTS applications without the use of transmit mask filters.
Each MAX2058/MAX2059 device yields 62dB/56dB of total adjustment range, +15dBm of output power, 32.3dBm/31.8dBm of OIP3, and a low spurious emission of -39.2dBc/-39.1dBc at a 200kHz offset, respectively. Besides the two digital attenuators and the two-stage RF amplifiers, these VGAs include an on-chip SPI decoder, two loopback switches, and a novel loopback mixer. When paired with the Company's MAX9491 synthesizer, the loopback mixer provides a means for translating the transmit signal frequency up or down so that it can be fed directly into the receiver band. With this feature, the system can be configured for simultaneous, real-time diagnostic monitoring of both the transmitter and receiver chains.
SOURCE: Maxim Integrated Products