Circuit and method for controlling charge injection in radio frequency switches

A method of controlling charge injection in a switch circuit, including:

• (a) employing a plurality of switching transistors, each having a gate configured to be coupled to a gate control signal and a gate-controlled channel, and being coupled in series through their respective gate-controlled channels, to selectively convey a signal from an input of the series coupled switching transistors to an output of the series coupled switching transistors;
• the series of switching transistors including:
• (1) at least one resistively-isolated node, each resistively-isolated node located between a different pair of the plurality of switching transistors in series;
• and
• (2) at least one non-resistively-isolated node located adjacent to one of the plurality of switching transistors in series;
• (b) generating injected charge at each resistively-isolated node;
• (c) operatively coupling one of a plurality of charge injection control transistors, each control transistor having a gate configured to be coupled to a charge injection control signal and a gate-controlled channel, between a corresponding one of the at least one resistively-isolated node and the at least one non-resistively-isolated node to selectively convey injected charge from the corresponding resistively-isolated node to the at least one non-resistively-isolated node;
• and
• (d) selectively switching each control transistor between an OFF-state and an ON-state in response to application of the charge injection control signal, and conveying injection charge only while in the ON-state.

A switch circuit, including:

• (a) a plurality of switching transistors, each having a gate configured to be coupled to a gate control signal and a gate-controlled channel, coupled in series through their respective gate-controlled channels to selectively convey a signal from an input of the series coupled switching transistors to an output of the series coupled switching transistors;
• the series of switching transistors including:
• (1) a plurality of gate resistors, wherein a gate of each switching transistor is connected to a corresponding one of the plurality of gate resistors, and wherein each gate resistor is connected to a control line that conveys a control signal to the gate of each corresponding switching transistor;
• (2) at least one resistively-isolated node, each resistively-isolated node located between a different pair of the plurality of switching transistors in series;
• and
• (3) at least one non-resistively-isolated node located adjacent to one of the plurality of switching transistors in series;
• (b) means for generating injected charge at each resistively-isolated node;
• and
• (c) control transistor switching means, operatively coupled to the generating means, each control transistor switching means having a gate configured to be coupled to a charge injection control signal and a gate-controlled channel, for selectively conveying injected charge from a corresponding one of the at least one resistively-isolated node to the at least one non-resistively-isolated node;
• wherein each control transistor switching means selectively switches between an OFF-state and an ON-state in response to application of the charge injection control signal, and conveys injection charge only while in the ON-state.

A radio-frequency (RF) signal switching circuit implemented as a monolithic integrated circuit (IC) on a semiconductor-on-insulator (SOI) substrate, including:

• (a) a plurality of signal switching MOSFET transistors, each MOSFET transistor having (A) a gate coupled to a gate resistor configured to be coupled to a gate control signal, each gate resistor having a resistance of approximately Rg, and (B) a gate-controlled channel, wherein the plurality of signal switching MOSFET transistors are coupled in series through their respective gate-controlled channels to selectively convey, in response to the gate control signal, an RF signal from an input of the series-coupled signal switching MOSFET transistors to an output of the series-coupled signal switching MOSFET transistors, the series-coupled signal switching MOSFET transistors further including:
• (1) at least one resistively-isolated node, each resistively-isolated node located between a different pair of the series-coupled signal switching MOSFET transistors and receiving injected charge when the plurality of series-coupled signal switching MOSFET transistors is switched from an ON state to an OFF state;
• and
• (2) at least one non-resistively-isolated node located adjacent to one of the plurality series-coupled signal switching MOSFET transistors;
• and
• (b) a plurality of charge injection control resistors, each charge injection control resistor operatively coupled between a corresponding one of the at least one resistively-isolated node and the at least one non-resistively-isolated node to convey received injected charge from the corresponding resistively-isolated node to the at least one non-resistively-isolated node, each charge injection control resistor having a resistance Rc approximately equal to Rg/N, wherein N is the number of transistors in the plurality of series-coupled signal switching MOSFET transistors.

A radio-frequency (RF) signal switching circuit implemented as a monolithic integrated circuit (IC) on a semiconductor-on-insulator (SOI) substrate, including:

• (a) a plurality of signal switching MOSFET transistors, each MOSFET transistor having (A) a gate coupled to a gate resistor configured to be coupled to a gate control signal, and (B) a gate-controlled channel, wherein the plurality of signal switching MOSFET transistors are coupled in series through their respective gate-controlled channels to selectively convey, in response to the gate control signal, an RF signal from an input of the series-coupled signal switching MOSFET transistors to an output of the series-coupled signal switching MOSFET transistors, the series-coupled signal switching MOSFET transistors further including:
• (1) at least one resistively-isolated node, each resistively-isolated node located between a different pair of the series-coupled signal switching MOSFET transistors and receiving injected charge when the plurality of series-coupled signal switching MOSFET transistors is switched from an ON state to an OFF state;
• and
• (2) at least one non-resistively-isolated node located adjacent to one of the plurality series-coupled signal switching MOSFET transistors;
• and
• (b) a plurality of charge injection control resistors, each charge injection control resistor operatively coupled between a corresponding one of the at least one resistively-isolated node and the at least one non-resistively-isolated node to convey received injected charge from the corresponding resistively-isolated node to the at least one non-resistively-isolated node, each charge injection control resistor having an impedance sufficiently high to prevent degradation of the RF isolation performance of the RF signal switching circuit and sufficiently low to effectively remove the received injected charge.

A radio-frequency (RF) signal switching circuit implemented as a monolithic integrated circuit (IC) on a semiconductor-on-insulator (SOI) substrate, including:

• (a) a plurality of signal switching MOSFET transistors, each MOSFET transistor having (A) a gate coupled to a gate resistor configured to be coupled to a gate control signal, and (B) a gate-controlled channel, wherein the plurality of signal switching MOSFET transistors are coupled in series through their respective gate-controlled channels to selectively convey, in response to the gate control signal, an RF signal from an input of the series-coupled signal switching MOSFET transistors to an output of the series-coupled signal switching MOSFET transistors, the series-coupled signal switching MOSFET transistors further including at least one resistively-isolated inner node, each inner node located between adjacent pairs of the series-coupled signal switching MOSFET transistors and receiving injected charge when the plurality of series-coupled signal switching MOSFET transistors is switched from an ON state to an OFF state;
• and
• (b) a plurality of charge injection control resistors, each charge injection control resistor operatively coupled between a corresponding inner node and at least one of the input or the output to convey received injected charge from the corresponding inner node to the input and/or the output, each charge injection control resistor having an impedance sufficiently high to prevent degradation of the RF isolation performance of the RF signal switching circuit and sufficiently low to effectively remove the received injected charge.