Loop filter capacitor multiplication in a charge pump circuit
AssigneeExar Corporation
InventorsShin Chung Chen, Vincent Wing Sing Tso
Life of this patent
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Abstract
A charge pump circuit with a small loop filter capacitor is disclosed in the invention. This is accomplished by providing multiple currents which add to the desired current, I. A switching circuit switches one of the currents through the capacitor, while directing a combination of the multiple currents through the resistors. In this way, a smaller current is provided through the capacitor, allowing the capacitor to be much smaller in size.
Claims8
A charge pump circuit comprising:
- a loop filter including at least a capacitor and a resistor;
- a current generating circuit for generating multiple currents;
- a switching circuit for switching one of said multiple currents through said capacitor, while directing a combination of said multiple currents through said resistor;
- such that a smaller current through said capacitor allows the capacitor to be smaller, wherein
- a first current of said multiple currents is diverted around said capacitor, and routed through said resistor;
- and
- a second current if said multiple currents is provided through said capacitor and through said resistor;
- such that the combination of said first and second currents are provided through said resistor while only said second current is provided through said capacitor.
A differential charge pump circuit comprising:
- a current generating circuit for generating multiple currents;
- a loop filter comprising a capacitor, a first resistor on a first side of said capacitor and a second resistor on a second side of said capacitor;
- a first switching transistor for providing a current of I * N - 1 N I
- through said first resistor, bypassing said capacitor;
- a second switching transistor for providing a current of I through said second resistor;
- and
- a third switching transistor for diverting a current of I*(N−1) from said current I after it passes through said second resistor, so it does not pass through said capacitor;
- such that a smaller current through said capacitor allows the effective capacitance of said capacitor to increase, wherein N is a number greater than zero.
A method for allowing an integrated capacitor in a loop filter of a change pump circuit comprising:
- generating multiple current;
- switching one of said multiple currents through said integrated capacitor, while directing a combination of said multiple currents through a resistor in said loop filter;
- such that a smaller current through said capacitor allows the effect in capacitance of said capacitor to increase;
- diverting a first current of said multiple currents around said capacitor, and routing said first current through said resistor, and
- routing a second current of multiple currents through said capacitor and through said resistor;
- and
- such that the combination of said first and second currents are routed through said resistor while only said second current is routed through capacitor.
Dependencies are inferred from the claim text.