Boosted charge transfer circuit
A charge transfer circuit, such as a charge coupled device or other bucket brigade device, which incorporates an amplifier to assist with charge transfer.
1. An apparatus for transferring charge in a charge-domain signal processing circuit, comprising:
an input charge holding device having a first terminal, disposed in series with and directly coupled to a first voltage input charge source, for holding an input charge;
an output charge holding device, for holding an output charge;
a charge transfer device, having an input terminal, an output terminal, and a control terminal, the input terminal coupled to a second terminal of the input charge holding device, the input terminal thereof not being directly coupled to the input charge source, and the the output terminal coupled to provide charge to the output charge holding device under control of a charge transfer control signal applied to the control terminal; and
an amplifier, having a first input coupled to the second terminal of the input charge holding device, a second input coupled to a reference voltage, and an output terminal coupled to the control terminal of the charge transfer device, for providing the charge transfer control signal, the amplifier configured to control a voltage at the control terminal of the charge transfer device to increase the rate at which the voltage at the input terminal of the charge transfer device settles to the reference voltage.
2. An apparatus as in claim 1 wherein the amplifier provides a gain between approximately 10 and approximately 100.
3. An apparatus as in claim 1 wherein the amplifier comprises an NFET and PFET, each having a terminal connected to a common node, the common node providing the output terminal of the amplifier.
4. An apparatus as in claim 3 wherein a drain terminal of the PFET is connected to a supply voltage, a drain terminal of the NFET is connected to a ground voltage, a gate terminal of the PFET is connected to a bias voltage, and a gate terminal of the NFET is connected to the input terminal of the charge transfer device.
5. An apparatus as in claim 3 wherein the common node is connected to the control terminal of the charge transfer device.
6. An apparatus as in claim 3 additionally comprising:
a source-follower PFET coupled between the NFET and the input terminal of the charge transfer device.
7. An apparatus as in claim 3 , further comprising a second NFET coupled between the input terminal of the charge transfer device and the NFET.
8. An apparatus as in claim 1 additionally comprising:
a first resistive element coupled between the input charge holding device and the first voltage input charge source;
a second resistive element coupled between the input charge holding device and the charge transfer device.
9. An apparatus as in claim 1 additionally comprising:
a current control FET, coupled between the output terminal of the amplifier and a ground voltage, to control ON and OFF times of the charge transfer device.
10. An apparatus as in claim 3 additionally comprising:
a power control FET coupled between the PFET and a supply voltage.
11. An apparatus as in claim 1 additionally comprising:
a first input charge control switch, coupled in series between the first voltage input charge source and the input charge holding device; and
a second input charge control switch, coupled in series between the input terminal of the charge transfer device and a second voltage input source.
12. An apparatus as in claim 1 wherein the charge transfer device comprises a diffusion region formed in a substrate, with a first control electrode formed on the substrate and providing the charge transfer device input terminal.
13. The apparatus of claim 12 additionally comprising a second control electrode formed on the substrate and providing the output charge holding terminal.
14. The apparatus of claim 1 , wherein the amplifier comprises a current source coupled to the output terminal of the amplifier.
15. The apparatus of claim 14 , wherein the amplifier further comprises a voltage buffer configured to isolate voltage between the input terminal and the control terminal of the charge transfer device.
16. The apparatus of claim 1 , further comprising a resistive element coupled to the input charge holding device.
17. The apparatus of claim 16 , wherein the resistive element is configured to reduce a non-linear signal distortion during a transfer of charge between the input charge holding device and output charge holding device.
18. The apparatus of claim 17 , wherein the resistive element is coupled in series between the input charge holding device and the input terminal of the charge transfer device.
19. The apparatus of claim 17 , wherein the resistive element is coupled between an input voltage and the input charge holding device.
20. The apparatus of claim 17 additionally comprising an additional resistive element coupled to the input charge holding device.
21. The apparatus of claim 14 additionally comprising a switch for disabling current through the charge transfer device and the current source, in response to a power switch control signal.
22. An apparatus for transferring charge, comprising:
an input charge holding device, for holding an input charge;
a charge transfer device comprising:
an element having an input terminal, an output terminal, and a control terminal, the input terminal coupled to receive charge from the input charge holding device, a second input terminal coupled to a reference voltage, and the output terminal coupled to provide charge under control of a charge transfer control signal applied to the control terminal; and
a second element, for holding an output charge, and coupled to receive charge from the first element; and
an amplifier for providing the charge transfer control signal, the amplifier having a first input terminal coupled to the input charge holding device, a second input terminal coupled to a reference voltage, and an output terminal coupled to the control terminal of the first element, the amplifier increasing a voltage of the charge transfer control signal relative to a voltage at the input terminal of the first element to increase the rate at which the voltage at the input terminal of the first element settles to the reference voltage.
23. The apparatus of claim 22 , wherein the amplifier comprises a current source coupled to the output terminal.
24. The apparatus of claim 22 , further comprising a resistive element coupled to the input charge holding device and configured to reduce a non-linear signal distortion during a transfer of charge between the input charge holding device and the second element of the charge holding device.