Linear Technology LTM9004/LTM9005 RF-to-digital µModule receivers

Click2Contact

Linear Technology has introduced the LTM9004 and LTM9005, two RF-to-digital µModule receivers that integrate the key components for 3G and 4G base station receivers (WCDMA, TD-SCDMA, LTE, etc) and smart antenna WiMAX base stations.

The integrated receivers offer a reduction in board space, integrating the RF mixer/demodulator, amplifiers, passive filtering and 14-bit, 125 Msps ADCs in one small package.

The 9004 implements a direct conversion architecture with an I/Q demodulator, low-pass filter and a dual ADC, while the 9005 implements an IF-sampling architecture with a downconverting mixer, SAW filter and a single ADC.

This level of integration enables smaller boards or higher channel count systems, alleviating issues related to separation and signal routing, while providing a reduction in design and debug time.

Two receiver architectures dominate base station designs: direct conversion and IF sampling. Direct conversion demodulates the RF signal and downconverts to DC (0 MHz in the frequency domain). This simplifies the filter, allowing low-pass filters with a 10 MHz cut-off (20 MHz signal bandwidth).

The 9004 implements this architecture. Other filter options are available for different signal bandwidths. IF sampling downconverts to an intermediate frequency, 140 MHz in this case, and the signal is demodulated in the digital domain.

The 20 MHz signal filtering is done with a surface acoustical wave filter integrated in the 9005. Other filter bandwidths are available.

Both devices are packaged in a 22 x 15 mm LGA package, using a multilayer substrate that shields sensitive analog lines from the digital traces to minimise digital feedback. Supply and reference bypass capacitance is placed inside the µModule, tightly coupled to the die, providing a space, cost and performance advantage over traditional packaging.