Switching device having a discharge circuit for improved intermodulation distortion performance
Radio-frequency (RF) switch circuits are disclosed providing improved switching performance. An RF switch system includes at least one field-effect transistor (FET) disposed between a first node and a second node, each having a respective source, drain, gate, and body. The system includes a coupling circuit including a first path and a second path, the first path being between the respective source or the respective drain and the respective gate of the at least one FET, the second path being between the respective source or the respective drain and the respective body of the at least one FET. The coupling circuit may be configured to allow discharge of interface charge from either or both of the coupled gate and body.
1. A radio-frequency (RF) switch comprising:
a field-effect transistor (FET) disposed between first and second nodes, the FET having a body and a gate; and
a coupling path connected between the body and gate, the coupling path including a resistor and a capacitor connected in series, such that the capacitor of the coupling path substantially blocks any and all DC current flow from the gate to the body and from the body to the gate.
2. The switch of claim 1 wherein the FET is a silicon-on-insulator (SOI) FET.
3. The switch of claim 1 wherein the coupling path consists of the capacitor and the resistor.
4. The switch of claim 3 wherein the capacitor and the resistor are selected to yield a desired intermodulation distortion (IMD) level of the switch, the desired IMD level being below a set threshold.
5. The switch of claim 1 further comprising a gate bias resistor connected in parallel with the gate and the coupling path.
6. The switch of claim 1 further comprising a body bias resistor connected in parallel with the body and the coupling path.
7. The switch of claim 1 wherein the first node is configured to receive an RF signal having a power value and the second node is configured to output the RF signal when the FET is in an ON state.
8. The switch of claim 7 further comprising N additional FETs connected in series with the FET, the quantity N selected to allow the switch circuit to handle the power value of the RF signal.
9. A method for fabricating a semiconductor die, the method comprising:
providing a semiconductor substrate;
forming a field-effect transistor (FET) on the semiconductor substrate, the FET having a gate and a body; and
forming a coupling circuit on the semiconductor substrate that is connected to the body and gate and includes a resistor and a capacitor connected in series, such that the capacitor of the coupling circuit substantially blocks any and all DC current flow from the gate to the body and from the body to the gate.
10. The method of claim 9 further comprising forming an insulator layer between the FET and the semiconductor substrate.
11. The method of claim 9 wherein the coupling circuit consists of the capacitor and the resistor.
12. A radio-frequency (RF) switch module comprising:
a packaging substrate configured to receive a plurality of components;
a semiconductor die mounted on the packaging substrate, the die including a field-effect transistor (FET); and
a coupling circuit that couples a body and a gate of the FET, the coupling circuit including a resistor and a capacitor connected in series, such that the capacitor of the coupling circuit substantially blocks any and all DC current flow from the gate to the body and from the body to the gate.
13. The switch module of claim 12 wherein the semiconductor die is a silicon-on-insulator (SOI) die.
14. The switch module of claim 12 wherein the coupling circuit consists of the capacitor and the resistor.
15. The switch module of claim 12 wherein the coupling circuit is part of the same semiconductor die as the FET.
16. The switch module of claim 12 wherein the coupling circuit is part of a second die mounted on the packaging substrate.
17. The switch module of claim 12 wherein the coupling circuit is disposed at a location outside of the semiconductor die.