Transformer-based balanced-impedance phase shifters for beamforming
A balanced impedance phase shifter (BIPS) beamforming system with reduced RF loss and power consumption is provided. The system includes multiple beamforming ports, multiple phase shifters, and a summing node at which the multiple phase shifters are connected in series. Each phase shifter includes a programmable admittance controlling phase shifting at a respective beamforming port of the phase shifter, and a transformer providing an interface between the respective beamforming port and the summing node. The multiple phase shifters may be configured to steer a beam formed by the multiple beamforming ports in one or more dimensions. A common-mode impedance at the summing node is independent of an impedance at the beamforming port. Each phase shifter may include an additional common-mode impedance that is configured to resonate with (or to remove) any parasitic common-mode impedances of the transformer on the summing node.
1 . A beamforming system comprising:
a plurality of beamforming ports;
a plurality of phase shifters; and
a summing node at which the plurality of phase shifters are connected in series,
wherein each phase shifter comprises:
a programmable admittance controlling phase shifting at a respective beamforming port of the phase shifter and in series connection with the programmable admittance of at least one other phase shifter in the plurality of phase shifters, wherein the programmable admittance comprises one or more digital tunable capacitors (DTCs) or digitally tunable reactive elements, and
a balun providing an isolation interface between the respective beamforming port and the summing node.
2 . The beamforming system of claim 1 , wherein the plurality of phase shifters are configured to steer a beam formed by the plurality of beamforming ports in one or more dimensions.
3 . The beamforming system of claim 1 , wherein the balun is an isolation transformer having a mutual inductance that is sized to realize a specified range of admittances when combined with the one or more DTCs or digitally tunable reactive elements.
4 . The beamforming system of claim 1 , wherein the balun is configured to provide a fixed reactance which when combined with a digitally tunable reactive element realizes a specified range of admittances.
5 . The beamforming system of claim 1 , wherein each phase shifter further comprises a crossover switch for selectively introducing one of a 0° phase shift and a 180° phase shift at the respective beamforming port.
6 . The beamforming system of claim 5 , further comprising a programming interface that provide control signals to control the programmable admittance and the crossover switch of each phase shifter.
7 . The beamforming system of claim 6 , wherein the programmable admittances and the crossover switches of the plurality of phase shifters are controlled to implement a balanced impedance tuning (BIT) algorithm.
8 . The beamforming system of claim 1 , wherein the programmable admittance is digitally controlled to vary from +jk/R s to −jk/R s , wherein R s is a port impedance at the respective beamforming port and k is a scaling factor set by a desired scan range.
9 . The beamforming system of claim 1 , wherein a common-mode impedance at the summing node is independent of a common-mode impedance at the beamforming ports.
10 . The beamforming system of claim 9 , wherein the balun is configured to provide isolation between the common-mode impedance at the beamforming ports and the common-mode impedance at the summing node.
11 . The beamforming system of claim 1 , wherein each phase shifter further comprises an additional common-mode impedance configured to resonate with a parasitic common-mode impedance of a circuit element at the summing node.
12 . The beamforming system of claim 1 , wherein the balun provides single-ended to differential conversion between the respective beamforming port and the summing node.
13 . The beamforming system of claim 1 , wherein each of the plurality of beamforming ports is attached to an antenna as part of a phased array.
14 . The beamforming system of claim 1 , wherein the beamforming system is a first phased array that is cascaded with a second phased array to form a larger phased array.
15 . An integrated circuit (IC) comprising: a plurality of beamforming ports; a plurality of phase shifters; and
a summing node at which the plurality of phase shifters are connected in series,
wherein each phase shifter comprises:
a programmable admittance controlling phase shifting at a respective beamforming port of the phase shifter and in series connection with the programmable admittance of at least one other phase shifter in the plurality of phase shifters, wherein the programmable admittance comprises one or more digital tunable capacitors (DTCs) or digitally tunable reactive elements, and
a balun providing an isolation interface between the respective beamforming port and the summing node.
16 . A phased array comprising:
a plurality of radiating elements;
a beamforming system comprising:
a plurality of beamforming ports connected to the plurality of radiating elements,
a plurality of phase shifters, and
a summing node at which the plurality of phase shifters are connected in series,
wherein each phase shifter comprises:
a programmable admittance controlling phase shifting at a respective beamforming port of the phase shifter and in series connection with the programmable admittance of at least one other phase shifter in the plurality of phase shifters, wherein the programmable admittance comprises one or more digital tunable capacitors(DTCs) or digitally tunable reactive elements, and
a balun providing an isolation interface between the respective beamforming port and the summing node.
17 . The phased array of claim 16 , further comprising a programming interface that provide control signals to control the programmable admittance of each phase shifter.
18 . The phased array of claim 16 , wherein each phase shifter further comprises an additional common-mode matching network that is configured to resonate with a parasitic common-mode impedance of the balun.
19 . The phased array of claim 16 , wherein leakage inductances in a primary and a secondary of the balun are used to resonate out at least some parasitic elements in the beamforming system.