Method and apparatus for switching of shunt and through switches of a transceiver
A switching network and associated method for operating within a transceiver are disclosed. The switching network has a timing control circuit that offsets the time at which a through switch and a shunt switch transition between on and off states. The output of the timing control circuit is an inverted and delayed version of a control signal applied to the input of the timing control circuit. Controlling the timing of the shunt switch provides a means to safely discharge any accumulated charge within the capacitance C gs between the gate and source of transistors included within the through switch.
1. An input control circuit for a low noise amplifier, including:
(a) a through switch configured to receive a radio frequency (RF) signal and selectively settable to pass the received RF signal to a terminal or block the received RF signal from the terminal; and
(b) a shunt switch coupled between the terminal and circuit ground and configured to selectively suppress transient voltages at the terminal after the through switch is set to pass the received RF signal to the terminal.
2. The input control circuit of claim 1 , further including an LNA having an input coupled to the terminal.
3. The input control circuit of claim 2 , further including a bias control circuit having a control input and a bias output, the bias output coupled to the LNA input and the bias output providing a bias signal in response to inputs applied to the control input of the bias control circuit.
4. The input control circuit of claim 1 , further including a three-port circulator having a first circulator port configured to be coupled to an antenna, a second circulator port coupled to a transmit amplifier, and a third circulator port being coupled to the through switch.
5. An input control circuit for a low noise amplifier, including:
(a) a through switch configured to receive a radio frequency (RF) signal and selectively pass the received RF signal to a terminal in response to a first control signal; and
(b) a shunt switch coupled between the terminal and circuit ground and configured to selectively couple the terminal to circuit ground in response to a second control signal;
wherein the second control signal causes the shunt switch to transition from closed to open only after the first control signal causes the through switch to transition from open to closed.
6. The input control circuit of claim 5 , wherein the shunt switch remains closed after the first control signal causes the through switch to transition from open to closed for an amount of time sufficiently long to suppress transient voltages at the terminal.
7. The input control circuit of claim 5 , wherein the through switch includes at least one field effect transistor (FET) having a capacitance when open and wherein the shunt switch remains closed after the first control signal causes the through switch to transition from open to closed for an amount of time sufficiently long to permit a substantial amount of the charge accumulated in the through switch capacitance to discharge through the shunt switch.
8. The input control circuit of claim 5 , further including an LNA having an input coupled to the terminal.
9. The input control circuit of claim 8 , further including a bias control circuit having a control input and a bias output, the bias output coupled to the LNA input and the bias output providing a bias signal in response to inputs applied to the control input of the bias control circuit.
10. The input control circuit of claim 5 , further including a three-port circulator having a first circulator port configured to be coupled to an antenna, a second circulator port coupled to a transmit amplifier, and a third circulator port being coupled to the through switch.
11. An input control circuit for a low noise amplifier, including:
(a) a through switch configured to receive a radio frequency (RF) signal and selectively pass the received RF signal to a terminal;
(b) a shunt switch coupled between the terminal and circuit ground and configured to selectively couple the terminal to circuit ground; and
(c) a timing control circuit coupled to the shunt switch and configured to transition the shunt switch from a closed state to an open state only after the through switch transitions from an open state to a closed state.
12. The input control circuit of claim 11 , wherein the shunt switch remains closed after the through switch transitions from an open state to a closed state for an amount of time sufficiently long to suppress transient voltages at the terminal.
13. The input control circuit of claim 11 , wherein the through switch includes at least one field effect transistor (FET) having a capacitance when open and wherein the shunt switch remains closed after the through switch transitions from an open state to a closed state for an amount of time sufficiently long to permit a substantial amount of the charge accumulated in the through switch capacitance to discharge through the shunt switch.
14. The input control circuit of claim 11 , further including an LNA having an input coupled to the terminal.
15. The input control circuit of claim 14 , further including a bias control circuit having a control input and a bias output, the bias output coupled to the LNA input and the bias output providing a bias signal in response to inputs applied to the control input of the bias control circuit.
16. The input control circuit of claim 11 , further including a three-port circulator having a first circulator port configured to be coupled to an antenna, a second circulator port coupled to a transmit amplifier, and a third circulator port being coupled to the through switch.