The present invention will now be described by way of example, only and not in any limitative sense, with reference to the accompanying drawings in which
FIG. 1 shows a known antenna switch arm;
FIG. 2 shows a first embodiment of a linear antenna switch arm according to the invention;
FIG. 3 shows a second embodiment of a linear antenna switch arm according to the invention;
FIG. 4 shows a third embodiment of a linear antenna switch arm according to the invention;
FIG. 5 shows a fourth embodiment of a linear antenna switch arm according to the invention;
FIG. 6 shows a fifth embodiment of a linear antenna switch arm according to the invention;
FIG. 7 shows a sixth embodiment of a linear antenna switch arm according to the invention;
FIG. 1 shows, in schematic form, a known antenna switch arm 1. The antenna switch arm 1 comprises first and second field effect transistors 2, 3 connected in series with the drain 4 of one transistor 2 connected to the source 5 of the next. The source 6 of one transistor 2 is connected to a signal input port 3. The drain 8 of the other is connected to a signal output port 9. A shunt resistor 10 extends between the input and output ports 7, 9.
In the off configuration, the impedance between the ports 7, 9 is RDS in parallel with CFET (the off capacitance of the FETs) which is highly non linear. In the on configuration the RDS is shorted out.
Shown in FIG. 2 is a linear antenna switch arm 10 according to the invention. The arm 10 comprises a plurality of FETs 11 connected in series with the drain of one FET 11 being connected to the source of the next, the connections between the FETs being joins 12. The source of one end transistor 11 is connected to a signal input port 13. The drain of the other end transistor 11 is connected to a signal output port 14. A signal line 15 extends between the input and output ports 13, 14.
One of the joins 17 is connected to the signal line 15 at a node 16 by a connection line 17. The connection line 17 includes a resistor 18. The signal line 15 includes a resistor 19 between the node 16 and the output port 14.
In use the connection line 17 fixes the voltage at the join 12 with a high value resistor 18. This significantly improves the linearity of the linear antenna switch arm 10.
Shown in FIG. 3 is a further embodiment of a linear antenna switch arm 10 according to the invention. This embodiment is similar to that of FIG. 2 except the resistor 19 in the signal line 15 is between the input port 13 and the node 16.
Shown in FIG. 4 is a further embodiment of a linear antenna switch arm 10 according to the invention. In this embodiment a plurality of joins 12 are connected to the signal line 15 at nodes 16 by connection lines 17. Each connection line 17 includes a resistor 18. Resistors are not included in the signal line 15 between the nodes 16. The nodes 16 are essentially short circuited together by the signal line 15. Again, the connection lines 17 pin the voltages at the joins 12 so improving the linearity of the linear antenna switch arm 10.
Shown in FIG. 5 is a further embodiment of a linear antenna switch arm 10 according to the invention. This embodiment is similar to that of FIG. 4 except each of the connection lines 17 includes a diode 20 in addition to a resistor 18.
Shown in FIG. 6 is a further embodiment of a linear antenna switch arm 10 according to the invention. This embodiment is similar to the embodiment of FIG. 5 except not all of the connection line 17 include a diode 20.
Shown in FIG. 7 is a further embodiment of a linear antenna switch arm 10 according to the invention. This embodiment includes a diode 21 in the signal line.
In all of these embodiments the gates of the FETs 11 are connected to a control line 22 by resistors 23 for turning the FETs on and off.
Patent Application
20080042913
