7 research outputs found
Multi-beam 4 GHz Microwave Apertures Using Current-Mode DFT Approximation on 65 nm CMOS
A current-mode CMOS design is proposed for realizing receive mode multi-beams
in the analog domain using a novel DFT approximation. High-bandwidth CMOS RF
transistors are employed in low-voltage current mirrors to achieve bandwidths
exceeding 4 GHz with good beam fidelity. Current mirrors realize the
coefficients of the considered DFT approximation, which take simple values in
only. This allows high bandwidths realizations using simple
circuitry without needing phase-shifters or delays. The proposed design is used
as a method to efficiently achieve spatial discrete Fourier transform operation
across a ULA to obtain multiple simultaneous RF beams. An example using 1.2 V
current-mode approximate DFT on 65 nm CMOS, with BSIM4 models from the RF kit,
show potential operation up to 4 GHz with eight independent aperture beams.Comment: 7 pages, 4 figures, In: IEEE International Microwave Symposium 201
Frequency-Multiplexed Array Digitization for MIMO Receivers: 4-Antennas/ADC at 28 GHz on Xilinx ZCU-1285 RF SoC
Communications at mm-wave frequencies and above rely heavily on beamforming antenna arrays. Typically, hundreds, if not thousands, of independent antenna channels are used to achieve high SNR for throughput and increased capacity. Using a dedicated ADC per antenna receiver is preferable but it\u27s not practical for very large arrays due to unreasonable cost and complexity. Frequency division multiplexing (FDM) is a well-known technique for combining multiple signals into a single wideband channel. In a first of its kind measurements, this paper explores FDM for combining multiple antenna outputs at IF into a single wideband signal that can be sampled and digitized using a high-speed wideband ADC. The sampled signals are sub-band filtered and digitally down-converted to obtain individual antenna channels. A prototype receiver was realized with a uniform linear array consisting of 4 elements with 250 MHz bandwidth per channel at 28 GHz carrier frequency. Each of the receiver chains were frequency-multiplexed at an intermediate frequency of 1 GHz to avoid the requirement for multiple, precise local oscillators (LOs). Combined narrowband receiver outputs were sampled using a single ADC with digital front-end operating on a Xilinx ZCU-1285 RF SoC FPGA to synthesize 4 digital beams. The approach allows -fold increase in spatial degrees of freedom per ADC, for temporal oversampling by a factor of
Towards a Low-SWaP 1024-beam Digital Array: A 32-beam Sub-system at 5.8 GHz
Millimeter wave communications require multibeam beamforming in order to
utilize wireless channels that suffer from obstructions, path loss, and
multi-path effects. Digital multibeam beamforming has maximum degrees of
freedom compared to analog phased arrays. However, circuit complexity and power
consumption are important constraints for digital multibeam systems. A
low-complexity digital computing architecture is proposed for a
multiplication-free 32-point linear transform that approximates multiple
simultaneous RF beams similar to a discrete Fourier transform (DFT). Arithmetic
complexity due to multiplication is reduced from the FFT complexity of
for DFT realizations, down to zero, thus yielding a
46% and 55% reduction in chip area and dynamic power consumption, respectively,
for the case considered. The paper describes the proposed 32-point DFT
approximation targeting a 1024-beams using a 2D array, and shows the
multiplierless approximation and its mapping to a 32-beam sub-system consisting
of 5.8 GHz antennas that can be used for generating 1024 digital beams without
multiplications. Real-time beam computation is achieved using a Xilinx FPGA at
120 MHz bandwidth per beam. Theoretical beam performance is compared with
measured RF patterns from both a fixed-point FFT as well as the proposed
multiplier-free algorithm and are in good agreement.Comment: 19 pages, 8 figures, 4 tables. This version corrects a typo in the
matrix equations from Section