Low loss reflective passive phase shifter using time delay element with double resolution
A phase shifter for altering the phase of a radio frequency signal is disclosed herein. A Lange coupler is used having reflective ports that are coupled to artificial transmission lines. The artificial transmission lines provide a reflection transmission path, the length of which can be determined by digital control lines. Transistors placed along the length of the central trace provide independent paths to ground that serve to shorten the electrical length of the ATL. Accordingly, by selectively turning the transistors on/off, the electrical length of the ATL can be selected and thus the amount of phase delay introduced by the phase shifter.
1. A phase shifter comprising:
(a) a radio frequency coupler having an input port, direct port, coupled port and isolation port;
(b) a ground conductor substantially encircling at least the radio frequency coupler;
(c) a first central trace coupled to the direct port;
(d) a first plurality of switches coupled at intervals between the first central trace and the ground conductor;
(e) a second central trace coupled to the coupled port; and
(f) a second plurality of switches coupled at intervals between the second central trace and the ground conductor.
2. The phase shifter of claim 1 , wherein the first central trace has a first distal end coupled to the ground conductor and the second central trace has a second distal end coupled to the ground conductor.
3. The phase shifter of claim 1 , wherein the first central trace has a first distal end coupled to the ground conductor through a first resistance and the second central trace has a second distal end coupled to the ground conductor through a second resistance.
4. The phase shifter of claim 3 , wherein the switches of the first and second plurality of switches comprise field-effect transistors having an ON resistance, R ON , and the first and second resistances each have a resistance approximately equal to the ON resistance, R ON , of one of the field-effect transistors.
5. The phase shifter of claim 1 , wherein the switches of the first and second plurality of switches comprise field-effect transistors (FETs) having an ON resistance, R ON , and the FETs along the length of the first and second central traces have different R ON values.
6. The phase shifter of claim 5 , wherein the R ON values of the FETs decrease along the length of first and second central traces relative to the direct port and the coupled port, respectively.
7. The phase shifter of claim 1 , wherein an electrical length of the first central trace is determined by a closed switch of the first plurality of switches closest to the direct port, and an electrical length of the second central trace is determined by a closed switch of the second plurality of switches closest to the coupled port.
8. The phase shifter of claim 7 , wherein secondary reflections to the direct port are reduced by one or more other closed switches of the first plurality of switches farther from the direct port than the closest closed switch.
9. The phase shifter of claim 7 , wherein secondary reflections to the coupled port are reduced by one or more other closed switches of the second plurality of switches farther from the coupled port than the closest closed switch.
10. The phase shifter of claim 1 , wherein the switches of the first and second plurality of switches comprise field-effect transistors (FETs), and the FETs are tapered in size along the length of the first and second central traces.
11. The phase shifter of claim 10 , wherein the FETs taper in increasing size along the length of the first and second central traces relative to the direct port and the coupled port, respectively.
12. The phase shifter of claim 1 , wherein a first subset of the first plurality of switches and a second subset of the first plurality of switches are positioned on opposite sides of the first central trace, and a first subset of the second plurality of switches and a second subset of the second plurality of switches are positioned on opposite sides of the second central trace.
13. The phase shifter of claim 12 , wherein the first and second subsets of the first plurality of switches are aligned in pairs on opposite sides of the first central trace, and the first and second subsets of the second plurality of switches are aligned in pairs on opposite sides of the second central trace.
14. The phase shifter of claim 12 , wherein the first and second subsets of the first plurality of switches are staggered with respect to each other on opposite sides of the first central trace, and the first and second subsets of the second plurality of switches are staggered with respect to each other on opposite sides of the second central trace.
15. The phase shifter of claim 1 , wherein the first and second central traces each have two longitudinal sides, and further including:
(a) a first ground section spaced apart from and along a first longitudinal side of the first central trace;
(b) a second ground section spaced apart from and along a second longitudinal side of the first central trace;
(c) a third ground section spaced apart from and along a first longitudinal side of the second central trace; and
(d) a fourth ground section spaced apart from and along a second longitudinal side of the second central trace.
16. The phase shifter of claim 15 , wherein at least one of the first ground section and second ground section is parallel to the first central trace, and at least one of the third ground section and fourth ground section is parallel to the second central trace.
17. The phase shifter of claim 15 , wherein the spacing of at least one of the first ground section and second ground section with respect to the first central trace tapers, and the spacing of at least one of the third ground section and fourth ground section with respect to the second central trace tapers.
18. The phase shifter of claim 1 , further including an externally switched reactance coupled to the isolation port of the radio frequency coupler and configured to increase the resolution of the phase shifter.
19. A phase shifter comprising:
(a) a radio frequency coupler having an input port, direct port, coupled port and isolation port;
(b) a ground conductor substantially encircling at least the radio frequency coupler;
(c) a first central trace coupled to the direct port;
(d) a first plurality of switches coupled at intervals between the first central trace and the ground conductor;
(e) a second central trace coupled to the coupled port; and
(f) a second plurality of switches coupled at intervals between the second central trace and the ground conductor;
wherein the first and second central traces, the first and second plurality of switches, and the ground conductor are arrayed such that the total impedance along each of the first and second central traces will be the same when corresponding ones of the first and second plurality of switches are closed.
20. A phase shifter comprising:
(a) a radio frequency coupler having an input port, direct port, coupled port and isolation port;
(b) a ground conductor substantially encircling at least the radio frequency coupler;
(c) a first central trace coupled to the direct port;
(d) a first plurality of switches coupled at intervals between the first central trace and the ground conductor;
(e) a second central trace coupled to the coupled port; and
(f) a second plurality of switches coupled at intervals between the second central trace and the ground conductor;
wherein the phase shifter provides a programmable time delay as a function of a selected electrical length of the first and second central traces.