A 1.5-to-5.0GHz input-matched &#x002B;2dBm P<inf>1dB</inf> all-passive switched-capacitor beamforming receiver front-end in 65nm CMOS

Abstract

Phased arrays in CMOS for consumer communication bands aim to enhance receiver performance by exploiting beamforming with antenna arrays. Sensitivity increases with the number of antenna elements through array gain and interferers can be cancelled through the spatial filtering of the beam pattern [1]. For the latter, the linearity of the receiver before the beamforming summing point becomes a bottleneck as interferers are not cancelled yet. Phase shifting in the LO domain reduces the complexity in the signal path and enables the use of linear signal blocks, but has high requirements on the multi-phase LO generation [2]. On the other hand, a switched-capacitor phase shifter can be very linear, but is limited by the linearity of the necessary input matching and element summing gm-stages [3]. This paper proposes a fully passive phased array receiver front-end which implements impedance matching, phase shifting and element summing with only switched-capacitor stages for a high linearity.The principle of a vector modulator phase shifter is illustrated in Fig. 1. (top left). A phase shift φ between 0° and 90° can be accomplished by adding two orthogonal signal phases weighted by respectively the sine and cosine of φ. For a full 360° phase shift range, four signal phases are required. These phases can be accurately generated for a wide RF frequency band by performing downconversion with the 25% duty cycle clocked passive quadrature mixer in Fig. 1. (top right).

A 4-Element Phased-Array System With Simultaneous Spatial- and Frequency-Domain Filtering at the Antenna Inputs

“…Clearly remarkable P 1dB and NF are achieved, and the dynamic range at the antenna inputs is substantially improved compared to previous work. Comparing to [7] in which the 4-phase LO phase shifting in combination with vector modulation is adopted, here we use just 8-phase LO phase shifting (no amplitude control). This renders superior input referred P1dB and NF compared to [7] because we move the summation point to the antenna input.…”

“…Comparing to [7] in which the 4-phase LO phase shifting in combination with vector modulation is adopted, here we use just 8-phase LO phase shifting (no amplitude control). This renders superior input referred P1dB and NF compared to [7] because we move the summation point to the antenna input. However, with uniform phase shifting, less spatial angle resolution is achieved (3 bits compared to 5 bits in [7]), while the lack of amplitude control allows for less control in the beam pattern and sidelobe level.…”

“…This renders superior input referred P1dB and NF compared to [7] because we move the summation point to the antenna input. However, with uniform phase shifting, less spatial angle resolution is achieved (3 bits compared to 5 bits in [7]), while the lack of amplitude control allows for less control in the beam pattern and sidelobe level. [ +5.5..+11 (3) 0..+2.6 (4) …”

“…Beamforming based on LO-phase shifting can be more compact, but usually still exploits inductors [3]. In the low GHz frequency range, inductorless LO-phase shifting combined with vector modulation gained interest in recent years [4][5][6][7]. Digital techniques leveraging Moore's law are exploited to realize programmable phase shifts.…”

“…This requires a high dynamic range for the blocks preceding the summing node to handle full strength blocking signals. To improve blocking behavior, a fully passive switched-capacitor vector modulator was presented in [7], achieving a compression point P 1dB =+2 dBm, but at a high noise penalty (NF=18 dB).…”