Maxim - Fully programmable, multistate, dual analog + digital VGA reduces solution footprint by 31%

The MAX2062 can serve as either an IF or RF all-purpose VGA, interfacing directly with 50ohm systems operating over the 50MHz to 1000MHz frequency range. Since the stages within each path have their own RF input and RF output, the MAX2062 can be configured to optimize either noise figure (amplifier configured first within the cascade) or linearity (amplifier configured last). Alternately, it can be configured to provide a compromise between the two parameters (amplifier configured second). In its typical configuration (digital attenuator to analog attenuator to driver amplifier), the cascade yields a total gain range of 64dB, a maximum gain of 19.4dB, and a noise figure of 7.3dB. The cascaded linearity is equally impressive with +41dBm of OIP3, +56dBm of OIP2, and +19dBm of OP1dB performance. In a receiver application, this excellent linearity directly enhances the receiver's immunity to strong blocker signals. Second- and third-order harmonic distortion (HD2 and HD3) content is also limited to -55dBc and -72.7dBc, respectively. This performance eases the filtering requirements of close-in harmonics and leads to simpler and more cost-effective filter designs.

The device's unique rapid-fire gain-selection feature lets the user quickly access any of four customized digital attenuation states without incurring the delays associated with reprogramming the device through the SPI bus. The digital attenuator I/O is further reduced by a factor of either 5x or 2.5x (5 control bits vs. 1 or 2, respectively), depending on the number of states desired.

The dedicated 8-bit control DACs allow the user to easily adjust the analog attenuation in 0.12dB increments through a simple SPI command. By integrating this function, the device not only eliminates the need for separate control DACs and voltage references, but it also simplifies the overall design. No additional SPI peripherals need to be programmed, and no additional analog control lines must be routed on the PCB.

The MAX2062 incorporates nine unique circuit functions into a single, compact monolithic device. When compared to an equivalent circuit using two MAX2065 VGAs, this new dual VGA reduces the circuit's overall footprint by 31%. These cost and space savings enable the next generation of wireless infrastructure designs in which transceiver price and density issues are paramount.