Switched capacitor current reference circuit
AssigneeFreescale Semiconductor, Inc.
InventorsSanjay Kumar Wadhwa, Qadeer Ahmad Khan, Kulbhushan Misri
Life of this patent
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Abstract
A switched capacitor current reference circuit generates an almost constant reference current across the parameters of process, voltage and temperature. A reference voltage is generated within the circuit, which eliminates the need for an external reference voltage. The reference current is generated by applying the reference voltage across a resistor emulated with a pair of switched capacitor circuits.
Claims17
A switched capacitor current reference circuit for generating a substantially constant reference current, comprising:
- a first transistor having a collector connected to a first voltage and an emitter connected to a second voltage by way of first and second series connected resistors;
- a second transistor having a collector connected to the first voltage, an emitter connected to the second voltage by way of a third resistor, and a base connected to a base of the first transistor;
- an op amp having a positive input terminal connected to a node between the first and second resistors, a negative input terminal connected to a node between the emitter of the second transistor and the third resistor, and an output terminal;
- a third transistor having a first terminal connected to the output terminal of the op amp and a second terminal connected to a first node;
- a first switched capacitor circuit connected between the first node and the second voltage;
- a second switched capacitor circuit connected between the first node and the second voltage, wherein the second switched capacitor circuit is connected in parallel with the first switched capacitor circuit;
- and
- a feedback path connecting the first node to a second node between the bases of the first and second transistors, and wherein the reference current is provided at a third terminal of the third transistor.
A switched capacitor current reference circuit for generating a substantially constant reference current, comprising:
- a first transistor having a collector connected to a first voltage and an emitter connected to a second voltage by way of first and second series connected resistors;
- a second transistor having a collector connected to the first voltage, an emitter connected to the second voltage by way of a third resistor, and a base connected to a base of the first transistor;
- an op amp having a positive input terminal connected to a node between the first and second resistors, a negative terminal connected to a node between the emitter of the second transistor and the third resistor, and an output terminal;
- a third transistor having a first terminal connected to the output terminal of the op amp and a second terminal connected to a first node;
- a first switched capacitor circuit connected between the first node and the second voltage;
- a second switched capacitor circuit connected between the first node and the second voltage, wherein the second switched capacitor circuit is connected in parallel with the first switched capacitor circuit;
- a feedback path connecting the first node to a second node between the bases of the first and second transistors, and wherein the reference current is provided at a third terminal of the third transistor;
- a first low pass filter for reducing a ripple in the reference current connected between the third transistor and the first voltage;
- and
- a second low pass filter for reducing spikes at the second node connected between the first node and the bases of the first and second transistors, wherein a substantially stable reference voltage is generated at the first node.
Dependencies are inferred from the claim text.