Independent control of branch FETs for RF performance improvement
A FET-based RF switch architecture and method that provides for independent control of FETs within component branches of a switching circuit. With independent control of branch FETs, every RF FET in an inactive branch that is in an “open” (capacitive) state can be shunted to RF ground and thus mitigate impedance mismatch effects. Providing a sufficiently low impedance to RF ground diminishes such negative effects and reduces the sensitivity of the switch circuit to non-matched impedances.
1. A switch circuit having at least one switching branch, each switching branch including:
(a) at least two switches each configured to be coupled to respective external circuit elements;
(b) a common node coupled between the at least two switches; and
(c) a shunt circuit coupled to the common node and independently settable to a state that improves isolation between the external circuit elements.
2. The invention of claim 1 , wherein the shunt circuit of at least one switching branch is further independently settable to not improve isolation between the external circuit elements when such switching branch is inactive.
3. The invention of claim 1 , wherein the shunt circuit includes:
(a) a first shunt circuit switch coupled to the common node;
(b) a second shunt circuit switch coupled between the first shunt circuit switch and circuit ground;
(c) a signal port coupled between the first and second shunt circuit switches and selectively connectable to at least one of the external circuit elements; and
(d) an independent control circuit coupled to the first shunt circuit switch and configured to independently set a switching state for the first shunt circuit switch.
4. The invention of claim 1 , wherein the switch circuit includes at least two switching branches, and wherein each switching branch is settable to a state that improves isolation between the external circuit elements independently of any other switching branch.
5. The invention of claim 1 , wherein the shunt circuit of a first switching branch includes a corresponding first signal port, and the shunt circuit of a second switching branch includes a corresponding second signal port, and wherein in at least one mode of operation, the shunt circuit of the first switching branch is set to couple the first signal port to a first external circuit element through one of the at least two switches of the first switching branch, while the shunt circuit of the second switching branch is set to concurrently couple the second signal port to a second external circuit element through one of the at least two switches of the second switching branch.
6. A switchable branch circuit including:
(a) at least two switches each configured to be coupled to respective external circuit elements;
(b) a common node connected between the at least two switches; and
(c) an independently settable shunt circuit coupled to the common node;
wherein, within the switchable branch circuit:
in a first inactive mode, the shunt circuit is set to a first state and the at least two switches are set to an open state so as to shunt the common node to circuit ground in order to improve isolation between any external circuit elements connected to the switches, and
in an active mode, the shunt circuit is set to a second state and at least one switch is set to a closed state so as to enable coupling of the common node through such at least one closed state switch to the respective external circuit elements connected to such at least one closed state switch.
7. The invention of claim 6 , wherein in a second inactive mode, the shunt circuit is independently set to not improve isolation between the external circuit elements connected to the switches.
8. The invention of claim 6 , wherein the shunt circuit includes:
(a) a first shunt circuit switch coupled to the common node;
(b) a second shunt circuit switch coupled between the first shunt circuit switch and circuit ground;
(c) a signal port coupled between the first and second shunt circuit switches and selectively connectable to at least one of the external circuit elements; and
(d) an independent control circuit coupled to the first shunt circuit switch and configured to independently set a switching state for the first shunt circuit switch.
9. The invention of claim 6 , further including at least a second switchable branch circuit configured to be connected to the external circuit elements, wherein each switchable branch circuit is settable to a state that improves isolation between the external circuit elements independently of any other switchable branch circuit.
10. A switchable branch circuit including:
(a) at least two switches each configured to be connected to respective external circuit elements;
(b) a common node connected to and situated between the at least two switches; and
(c) a settable shunt circuit, the shunt circuit including:
(1) a first shunt circuit switch coupled to the common node;
(2) a second shunt circuit switch coupled between the first shunt circuit switch and circuit ground;
(3) a signal port coupled between the first and second shunt circuit switches and selectively connectable to at least one of the external circuit elements; and
(4) an independent control circuit coupled to the first shunt circuit switch and configured to independently set a switching state for the first shunt circuit switch;
wherein, within the switchable branch circuit:
in a first inactive mode, the first and second shunt circuit switches are set to a closed state and the at least two switches are set to an open state so as to shunt the common node to circuit ground in order to improve isolation between any external circuit elements connected to the switches, and
in an active mode, the first shunt switch circuit is set to a closed state, the second shunt circuit switch is set to an open state, and at least one switch is set to a closed state, so as to enable coupling of the signal port through the first shunt switch to the common node and to enable coupling of the common node through such at least one closed state switch to the respective external circuit elements connected to such at least one closed state switch.
11. The invention of claim 10 , further including at least a second switchable branch circuit configured to be connected to the external circuit elements, wherein each switchable branch circuit is settable to a state that improves isolation between the external circuit elements independently of any other switchable branch circuit.
12. The invention of claim 1 , 6 , or 10 , wherein at least one switch includes a stack of series connected FETs.
13. The invention of claim 3 , 8 , or 10 , wherein at least one shunt circuit switch includes a stack of series connected FETs.
14. The invention of claim 3 , 8 , or 10 , wherein at least one shunt circuit switch includes a variable impedance FET settable to an impedance between the impedance presented by the FET when in a fully open state or when in a fully closed state.