Increasing charge capacity of charge transfer circuits without altering their charge transfer characteristics
A technique for increasing the charge storage capacity of a charge storage device without changing its inherent charge transfer function. The technique may be used to implement a charge domain signal processing circuits such as Analog to Digital Converters (ADCs) used in digital radio frequency signal receivers.
1. A method for operating a charge transfer stage comprising:
precharging a node to a precharge voltage, wherein the node is coupled to a charge storage device;
transferring an input charge to the node via a charge transfer device, and as a result, causing a low voltage at the node to drop to a voltage in a range that includes a voltage that depends on a maximum possible input charge;
changing an applied voltage which is applied to the charge storage device from a first voltage to a second voltage;
at a later time, transferring charge from the node via the charge transfer device, and returning the applied voltage which is applied to the charge storage device to the first voltage; and
controlling the precharge voltage, the maximum possible input charge, the first voltage and the second voltage; such that a difference between the precharge voltage and the low voltage is less than a range of the applied voltage.
2. The method of claim 1 wherein the later time occurs substantially simultaneously with the step of transferring charge from the node.
3. The method of claim 1 wherein the later time occurs before completing the step of transferring charge from the node.
4. The method of claim 1 wherein the charge storage device comprises one or more capacitors.
5. The method of claim 1 wherein the charge transfer stage is part of a charge domain pipeline.
6. The method of claim 5 wherein the charge domain pipeline is part of an analog to digital converter.
7. The method of claim 6 wherein the analog to digital converter is part of a digital radio frequency signal receiver.
8. A method comprising:
(a) pre-charging a node to a precharge voltage, the charge transfer node coupled to a capacitor;
(b) transferring an input charge to the node via a charge transfer device, and as a result, causing a low voltage at the node to drop to a voltage in a range that depends on a maximum possible input charge;
(c) changing an applied voltage coupled to the capacitor from a first voltage to a second voltage;
(d) transferring charge from the node;
(e) at a time after step (d) is initiated, returning the applied voltage to the first voltage; and
(f) controlling the precharge voltage, the maximum possible input charge, the first voltage and second voltage such that a difference between the precharge voltage and the low voltage is less than a range of the applied voltage in step (c).
9. An apparatus comprising:
a node coupled to receive a precharge voltage at a first time, and to receive an injected input charge at a second time, such that a minimum voltage results on the node that is related to a maximum possible injected input charge;
a charge storage device, coupled to the node and also coupled to an applied voltage;
a signal generator, for changing the applied voltage from a first voltage to a second voltage at the second time when the injected input charge is received at the charge transfer node, and at a third time returning the applied voltage to the first voltage, and thereby transferring charge from the node and further for controlling the precharge voltage, the maximum possible injected input charge, the first voltage and the second voltage; such that a difference between the precharge voltage and the minimum voltage is less than a difference between the first and second voltages used as the applied voltage.
10. The apparatus of claim 9 wherein the third time occurs during transfer of charge from the node.
11. The apparatus of claim 9 wherein the third time occurs after initiating charge transfer from the node.
12. The apparatus of claim 9 wherein the charge storage device comprises one or more capacitors.
13. The apparatus of claim 9 wherein the node is part of a charge domain pipeline.
14. The apparatus of claim 13 wherein the charge domain pipeline is part of an analog to digital converter.
15. The apparatus of claim 14 wherein the analog to digital converter is part of a digital radio frequency signal receiver.