Electronic Design

Digital Predistortion Receiver Simplifies Base-Station Design

One 11.25-mm x 15-mm µModule package holds a wideband RF-to-digital receiver subsystem that includes a 12-bit, 250-Msample/s analog-to-digital converter (ADC), a bandpass filter, intermediate frequency (IF) amplifier, and a high-linearity RF downconverting mixer. The LTM9003 integrated µModule receiver reduces board space and development time for wireless base stations implementing PA linearization with digital predistortion (DPD). Powerful digital algorithms correct for nonlinearity in the power amplifier (PA), allowing it to operate at a higher average power level without generating excessive distortion. The LTM9003 includes a 125-MHz bandpass filter that exhibits less than 0.5-dB passband ripple across the entire band. The noise floor of the receiver chain from the RF input to the LVDS digital output is -147.3 dBm/Hz, which is well below that of the PA. Since DPD is a feedback loop, the receiver (also called a transmit observation path receiver) benefits from low latency; a faster loop leads to better efficiency in the PA and therefore even lower power consumption. The ADC in the LTM9003 has five clock cycles of latency and the absolute delay through the filter is 2.7 ns. The LGA package uses a multilayer substrate that shields sensitive analog lines from the digital traces to minimize digital feedback. Supply and reference bypass capacitance is placed inside the µmodule, tightly coupled to the die. With no external capacitance required, the LTM9003 consumes approximately one-fourth the space of discrete implementations. The LTM9003 is priced at $45.00 each in 1000-piece quantities. LINEAR TECHNOLOGY CORP., Milpitas, CA. (408) 432-1900.



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