Nuts and Volts - April 2014

Q DACs where they become analog signals. They are filtered to set the bandwidth somewhere in the 1.5 to 28 MHz range. The signals are amplified and fed to the mixer. The transmitter is the direct conversion type that upconverts the signals to the desired output frequency. An internal PLL synthesizer drives the mixer. The output is then amplified to + 3 dBm that is sufficient to drive an external power amplifier.

The dual receivers are at the bottom of Figure 4. Three LNAs accept inputs from the antenna by way of separate tuned circuits or filters. The mixer then downconverts these signals to baseband. Again, a direct conversion architecture is used where the receiver PLL is set to the receive frequency. The baseband signals are amplified and low pass filtered, amplified again, and fed to the I and Q ADCs. Some DSP operations occur on-chip before the digital signals go to the LimeLight interface bus for transport to the external DSP/FPGA.

As with the AD9361, the LMS7002M is fully programmable. It uses the SPI interface to send digital codes to set the operating frequencies, bandwidths, gains, and other parameters. The LMS7002M also has an onboard 8051 microcontroller to aid in the programming and configuration of the chip.

The LMS7002M comes in an 11. 5 mm x 11. 5 mm QFN package with 261 pins. It operates from a 1.8 volt supply.

Both of the radio chips make designing complex wireless devices relatively fast and easy. Because there is so much circuitry inside, it lessens the number of discrete external components needed, while cutting costs and minimizing printed circuit board space.