System and methods to improve the performance of semiconductor based sampling system
View Patent ↗Circuits and methods that improve the performance of electronic sampling systems are provided. Impedances associated with sampling semiconductor switches are maintained substantially constant during sample states, at least in part, by compensating for encountered input signal variations in order to reduce or minimize signal distortion associated with sampled signals that pass through the sampling switch.
1. A sampling circuit that operates in at least a sample state and a hold state comprising:
a semiconductor switch that operates in at least a non-conductive mode and a conductive mode as directed by an amount of charge applied to a control terminal, the semiconductor switch being coupled between a source of an input signal and an output terminal;
an initialization circuit that is operative to selectively couple an initialization signal at least partially representative of the input signal to the control terminal, during an initialization state;
a charge generator for producing a charge that is distinct from the input signal and coupled to the control terminal to control the switch; and
a control circuit that is operative to selectively direct the charge generator to deliver a predetermined amount of charge to the control terminal such that the impedance of the semiconductor switch during a sample state is maintained substantially constant.
2. The sampling circuit of claim 1 , wherein the initialization circuit is coupled to receive the input signal.
3. The sampling circuit of claim 2 , wherein the initialization circuit charge is at least partially provided by the input signal.
4. The sampling circuit of claim 1 , wherein the initialization circuit is activated when the semiconductor switch is in a non-conductive mode.
5. The sampling circuit of claim 1 , wherein the initialization circuit is inactive when the semiconductor switch is in a conductive mode.
6. The sampling circuit of claim 1 , further comprising an initialization controller that includes a discharge switch operative to deactivate the initialization circuit.
7. The sampling circuit of claim 1 , wherein the initialization circuit includes at least one semiconductor initialization switch coupled between the input signal source and the control terminal.
8. The sampling circuit of claim 1 , further comprising an initialization controller that comprises an initialization charge generator operative to activate the initialization circuit.
9. The sampling circuit of claim 8 wherein the initialization charge generator is coupled to a voltage multiplier circuit.
10. The sampling circuit of claim 9 , wherein the voltage multiplier is a charge pump.
11. The sampling circuit of claim 8 , wherein the initialization charge generator includes a pulse generation circuit responsive to a control signal.
12. The sampling circuit of claim 8 , wherein the initialization charge generator includes a current source responsive to a control signal.
13. The sampling circuit of claim 8 , wherein the initialization charge generator includes at least one initialization capacitor and one initialization charge sourcing switch.
14. The sampling circuit of claim 13 , wherein the initialization capacitor is a capacitor connected semiconductor device.
15. The sampling circuit of claim 1 , wherein the initialization circuit is configured to provide a first switchable coupling between the source of the input signal and the control terminal of the semiconductor switch and a second switchable coupling between the output terminal and the control terminal of the semiconductor switch.
16. A method of transitioning a semiconductor switch from a high impedance, substantially non-conductive state to a low impedance, substantially conductive state, the semiconductor switch being coupled between a source of an input signal and an output terminal, the method comprising:
determining a capacitance associated with the semiconductor switch control terminal when the semiconductor switch, in its conductive state, reaches a desired impedance value;
determining an amount of charge absorbed by the semiconductor switch control terminal capacitance when the semiconductor switch, in its conductive state, reaches a desired impedance value; and
providing a charge to a control terminal of the semiconductor switch which is substantially equal to or greater than the amount of charge absorbed by the gate to channel capacitance, such that the semiconductor switch turns ON, and an impedance of the semiconductor switch is maintained substantially constant.
17. The method of claim 16 , wherein the providing step further comprises charging at least one capacitor to a value which is substantially equal to or greater than the amount of charge absorbed by the semiconductor switch control terminal capacitance when the semiconductor switch, in its conductive state, reaches a desired impedance value.
18. The method of claim 17 , wherein the providing step further comprises coupling the charge of the at least one capacitor to the control terminal of the semiconductor switch and discharging the capacitor to turn the semiconductor switch ON.
19. The method of claim 18 , wherein the providing step further comprises discharging the at least one capacitor in response to a control signal.
20. The method of claim 18 , wherein the providing step further comprises maintaining energy discharged by the at least one capacitor on the control terminal to maintain the semiconductor switch ON.
21. The method of claim 16 , wherein the providing step further comprises providing a charge to the control terminal of the semiconductor switch which is substantially equal to or greater than the amount of charge absorbed by the gate to channel capacitance and any parasitic capacitance encountered in a transmission path and the control terminal.
22. The method of claim 18 , wherein the providing step further comprises coupling a current source to the control terminal of the semiconductor switch in response to a timing circuit.
23. The method of claim 16 , further comprising turning the semiconductor switch OFF by discharging the control terminal.
24. The method of claim 16 , wherein the step of providing a charge comprises coupling to the control terminal an initialization signal at least partially representative of the input signal.