Phased-Array antenna beam squinting related to frequency dependency of delay circuits

Abstract-Practical time delay circuits do not have a perfectly linear phase-frequency characteristic. When these delay circuits are applied in a phased-array system, this frequency dependency shows up as a frequency dependent beam direction (“beam squinting”). This paper quantifies beam squinting for a linear one-dimensional phased array with equally spaced antenna elements. The analysis is based on a (frequency-dependent) linear approximation of the phase transfer function of the delay circuit. The resulting relation turns out to be invariant for cascaded cells. Also a method is presented to design time-delay circuits to meet a maximum phased-array beam squinting requirement

Wideband RF beamforming: architectures, time-delays and CMOS implementations

A phased array antenna is a kind of antenna which is electronically reconfigurable to realize different antenna beam patterns. Delay blocks are an essential part of phased array antenna systems. Their delay-range, noise, nonlinearity, bandwidth, size, cost and power consumption have a dominant effect on the phased array antenna systems. This thesis targets CMOS implementation of delay cells suitable for compact IC implementations in standard CMOS processes, in the hundreds of MHz to low GHz range. A criterion f=0 has been introduced to quantify the delay vs. frequency variations in delay blocks. Mathematical formulas have been found that use f=0 of the delay blocks to quantify the beam direction variations in the phased array. As an approximate implementation of delay blocks, the existing gm-(R)C 1st order all-pass filters have been studied and a comparison method has been introduced to compare and benchmark them. Their circuit topologies shows that they are not directly cascade-able and have large parasitic capacitors which limit their bandwidth and are therefore unsuitable for working up to 3GHz. This has led us to the idea of a new topology for the 1st order all-pass filters. The new topology has much less parasitic components compared to other 1st order all-pass topologies, therefore it has a bandwidth up to 5x more compared to the aforementioned 1st order gm-(R)C filters. In order to demonstrate the functionality of the delay block, it has been designed and used in implementation of a 4 antenna element phased array antenna chip at 160nm technology and measurements results showed its bandwidth is wide enough to cover frequencies from 1GHz to 2.5GHz. Measurement results proved that the 1st order gm-C filters are suitable for the realization of the wideband phased array antenna system

Time delay circuits: A quality criterion for delay variations versus frequency

This paper shows that the group delay of a delay circuit does not give sufficient information to predict the delay vs. frequency. A new criterion (fϕ=0) is proposed that characterizes the delay variations over a specified frequency range. The mathematical derivation of fϕ=0 for a single delay block and a cascade of delay blocks is shown. As examples the criterion is applied to the design of an RC and LC delay block. Delay predictions based on fϕ=0 are compared with simulation results, showing reasonable agreement

A 1-to-2.5GHz phased-array IC based on gm-RC all-pass time-delay cells

Abstract Electronically variable delays for beamforming are generally realized by phase shifters. Although a constant phase shift can approximate a time delay in a limited frequency band, this does not hold for larger arrays that scan over wide angles and have a large instantaneous bandwidth. In this case true time delays are wanted to avoid effects such as beam-squinting. In this paper we aim at compactly integrating a delay based phased-array receiver in standard CMOS IC technology. This is for instance relevant for synthetic aperture radars, which require large instantaneous bandwidths often in excess of 1GHz, either as RF or as IF bandwidth in a superheterodyne system. We target low-GHz radar frequencies, assuming sub-arrays of four elements and up to 550ps delay

Frequency limitations of first-order gm-RC all-pass delay circuits

All-pass filter circuits can implement a time delay but, in practice, show delay and gain variations versus frequency, limiting their useful frequency range. This brief derives analytical equations to estimate this frequency range, given a certain maximum allowable budget for variation in delay and gain. We analyze and compare two well-known gm - RC first-order all-pass circuits, which can be compactly realized in CMOS technology and relate their delay variation to the main pole frequency. Modeling parasitic poles and putting a constraint on gain variation, equations for the maximum achievable pole frequency and delay variation versus frequency are derived. These equations are compared with simulation and used to design and compare delay cells satisfying given design goals

A compact quad-shank CMOS neural probe with 5,120 addressable recording sites and 384 fully differential parallel channels

Large-scale in vivo electrophysiology requires tools that enable simultaneous recording of multiple brain regions at single-neuron level. This calls for the design of more compact neural probes that offer even larger arrays of addressable sites and high channel counts. With this aim, we present in this paper a quad-shank approach to integrate as many as 5,120 sites on a single probe. Compact fully-differential recording channels were designed using a single-gain-stage neural amplifier with a 14-bit ADC, achieving a mean input-referred noise of 7.44 μVrms in the action-potential band and 7.65 μVrms in the local-field-potential band, a mean total harmonic distortion of 0.17% at 1 kHz and a mean input-referred offset of 169 μV. The probe base incorporates 384 channels with on-chip power management, reference-voltage generation and digital control, thus achieving the highest level of integration in a neural probe and excellent channel-to-channel uniformity. Therefore, no calibration or external circuitry are required to achieve the above-mentioned performance. With a total area of 2.2 × 8.67 mm2 and a power consumption of 36.5 mW, the presented probe enables full-system miniaturization for acute or chronic use in small rodents