Broadband complementary metal‐oxide semiconductor phase shifter with 6‐bit resolution based on all‐pass networks

Abstract

Multi‐stage all‐pass networks can be used to realise broadband phase shifters with low phase error. In this study, single‐stage and two‐stage all‐pass networks with internal switched capacitors are investigated. Potentials and limitations of using the all‐pass networks with internal switched capacitors for phase shifter design are examined. On the basis of the single‐stage and two‐stage all‐pass networks, a fully‐differential digital phase shifter with 6‐bit resolution is designed. The digital phase shifter is implemented using a 0.18‐μm complementary metal‐oxide semiconductor process. The chip area is 2.80 × 1.75 mm2. Measurement results show that minimum root‐mean‐square phase error of 2° is achieved from 2.19 to 2.82 GHz, which translates into a bandwidth (BW) of 25%. The average insertion loss is 14.6 dB at the design frequency of 2.4 GHz. Over the entire BW, the return loss is greater than 9.2 dB and the amplitude error is within ±1 dB.

Variable-Phase All-Pass Network Synthesis and Its Application to a 14–54 GHz Multiband Continuous-Tune Phase Shifter in Silicon

“…Another potential issue is the use of a tuning voltage for the phase-control, which could be implemented using a digital-toanalog control (DAC) [12], [20], [38]. Notice that a single tuning voltage is used to control all varactors, opposed to two in [38] and four in [12].…”

“…The last term of (19) shows that the losses of the capacitor, and by extent the Q-factor, are defined by the on-resistance of the MOS transistor. Combining that with (18) and (20), we observe the design trade-off for the digitally variable capacitors MOS transistors. While increasing M sw width leads to a lower on-resistance -reducing losses and frequency dependency of C on,tot -it also increases the capacitances to bulk, further increasing C off,tot .…”

“…This embedding potentially reduces the number of switches, reducing losses and form-factor of the phase-shifter. Embedding the switch has been effectively addressed in bypass/lowpass [9] and bypass/all-pass phase-shifters [14], but remains rather unexplored in all-pass/all-pass implementations [18], [20], especially at mm-wave frequencies. By enabling all-pass networks (APNs) with embedded switch/phase-control, both the form-factor and losses of APN-based phase-shifters could be further reduced, leading to more competitive devices with additional multi-band capability.…”

“…From now onwards, we will address the APNs with embedded switch/phase-control as Variable-Phase All-Pass Networks (VP-APNs), since both phase-states are APNs. VP-APNs are found in literature in two flavors, having digital phase-control through switched-capacitors [18], [20] or analog phase-control through varactors [21]- [24].…”

“…Digitally-controlled VP-APNs were studied before in the context of microwaves, first implemented using magneticallycoupled inductors in a combination of CMOS and an integrated passive device (IPD) carrier [18]. By implementing inductors in the IPD carrier, higher-Q inductors are obtained In [20], a purely CMOS phase-shifter was fabricated, with a much-reduced bandwidth and higher losses due to both lower-Q inductors and higher resolution. The high losses obtained in [18], [20] at microwaves illustrate the potential challenges of scaling up frequencies in VP-APNs, thus requiring a shift in paradigm to successfully implement these devices at mmwaves.…”