Switchable current source circuit and method
First Claim
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1. A switching circuit for providing a switched current source output, comprising:
- a reference voltage input device, which comprises a reference voltage charge storage device;
a gate voltage charge storage arrangement for storing a precharge voltage derived from the reference voltage;
a reference current source providing a reference current;
an output transistor;
a current sensing transistor for generating a sense current dependent on the current source output and which is supplied by the reference current source;
an isolating switch arrangement for selectively coupling or isolating the gate of the output transistor and the gate of the current sensing transistor to or from the gate voltage charge storage arrangement;
a discharge switch arrangement for discharging the gate of the output transistor and the gate of the current sensing transistor;
a feedback loop for controlling the reference voltage stored on the reference voltage charge storage device to maintain the sense current substantially equal to the reference current.
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Abstract
A switchable current source in which a reference voltage value to be used in driving the gate of an output transistor is sampled and stored. The reference voltage is derived using a reference current source which feeds a current sensing transistor. The current sensing transistor is turned off when the output transistor is turned off, so that the reference current source then does not consume power. A large reference current Iref can then be used for a short time.
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Citations
8 Claims
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1. A switching circuit for providing a switched current source output, comprising:
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a reference voltage input device, which comprises a reference voltage charge storage device; a gate voltage charge storage arrangement for storing a precharge voltage derived from the reference voltage; a reference current source providing a reference current; an output transistor; a current sensing transistor for generating a sense current dependent on the current source output and which is supplied by the reference current source; an isolating switch arrangement for selectively coupling or isolating the gate of the output transistor and the gate of the current sensing transistor to or from the gate voltage charge storage arrangement; a discharge switch arrangement for discharging the gate of the output transistor and the gate of the current sensing transistor; a feedback loop for controlling the reference voltage stored on the reference voltage charge storage device to maintain the sense current substantially equal to the reference current. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification