Data converter digital assistance
Data converter analog performance will continue to improve and these improvements at the analog level will include increased sampling rates for wider bandwidth, increased channel count, and maintaining the key performance metrics of noise, density, and linearity. These benefits will drive all of the RF signal chain solutions described, aiding new phased array solutions. An area of increased importance at the system level is the recent addition of many digital functions (as shown in figure 4) that can be used to offload FPGA processing and help the overall system.
Recently released data converters include digital downconversion and filtering, which potentially reduce the data rate to the FPGA, reducing system power and FPGA processing requirements. Emerging Analog Devices data converters will continue to add functionality, such as equalization and features at the front end of the digital beamforming processing.
At high frequencies or for low power systems, an every element system is challenged by size and power requirements. The use of analog beamforming reduces the number of waveform generator and receiver channels required to be digitized. Analog beamforming of phased array antennae is accomplished by adjusting the phase of the signal in individual elements to steer the direction of the radiation pattern or beam. Figure 5a shows a generic analog beamforming example. Phase shifters are provided on both transmit/receive for beam steering, and many elements are combined to a single output. Figure 5b shows a functionally equivalent example where the phase shifter and attenuator are common to both the transmitter and receiver path enabled by microwave switches. The later topology reduces the number of phase shifters and attenuators required, but may require more frequent command updates to the devices.