RF-to-digital uModule receivers
25 October 2010
Linear Technology introduces the LTM9004 and LTM9005, two RF-to-digital uModule receivers.
The modules integrate the key components for 3G and 4G base station receivers (WCDMA, TD-SCDMA, LTE) and smart antenna WiMAX base stations. The integrated receivers offer a dramatic reduction in board space, integrating the RF mixer/demodulator, amplifiers, passive filtering and 14bit, 125Msps ADCs in a small package.
The LTM9004 implements a direct conversion architecture with an I/Q demodulator, low-pass filter and a dual ADC. The LTM9005 implements an IF-sampling architecture with a down-converting mixer, SAW filter and a single ADC. This high level of integration enables smaller boards or higher channel count systems, alleviating issues related to separation and routing of signals, while providing a significant reduction in design and debug time. These receivers harness years of signal chain design experience and offer it in an easy-to-use 22mm x 15mm µModule package.
Cellular service providers are under intense pressure to reduce capital (CAPEX) and operating (OPEX) expenses. Supporting trends include the need for smaller, lighter, lower power base stations such as remote radio heads (RRH) that can be mounted on the tower with the antenna; and high density, high channel-count macrocell base stations with higher efficiency; and the use of small, digital repeaters.
These uModule receivers address these trends. At only 25% of the board space area of discrete designs, the LTM9004 and LTM9005 save critical space and also reduce the time and effort required for optimising the design and layout of dozens of high frequency components. This leads to lower development costs, fewer components to source and stock, and faster time to market.
Two receiver architectures dominate base station designs: direct conversion and
IF-sampling. Direct conversion demodulates the RF signal and down-converts to DC (0MHz in the frequency domain). This simplifies the filter, allowing low-pass filters with a 10MHz cut-off (20MHz signal bandwidth). The LTM9004 implements this architecture. Other filter options are available for different signal bandwidths. IF-sampling down-converts to an intermediate frequency (IF), 140MHz in this case, and the signal is demodulated in the digital domain. The 20MHz signal filtering is done with a surface acoustical wave (SAW) filter integrated in the LTM9005. Other filter bandwidths are available.
The LTM9004 and LTM9005 are packaged in a space-saving 22mm x 15mm LGA package, utilising a multilayer substrate that shields sensitive analogue lines from the digital traces to minimise digital feedback. Supply and reference bypass capacitance is placed inside the uModule package, tightly coupled to the die, providing a space, cost and performance advantage over traditional packaging.
The LTM9004 and LTM9005 are sampling now with production volumes next quarter. Demo boards and samples are available.
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