Switched capacitor bandgap reference circuit
AssigneeAnalog Devices, Inc.
InventorPatrick J. Garavan
Life of this patent
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Abstract
A circuit is provided which is adapted to compensate for the inherent parasitic capacitance which is implicit in switched capacitor circuits. By shielding the parasitic capacitance to a common node of the circuit and then connecting this shield to a voltage source that tracks the voltage change at the input to an amplifier, the present invention provides a bootstrapping effect that enables a minimization of the effect of the parasitic capacitance. The invention also provides a circuit that is adapted to compensate for curvature in the output of a switched capacitor bandgap reference.
Claims36
A switched capacitor bandgap reference circuit comprising:
- a) a first transistor adapted to operate at a first current density so as to provide a first transistor output,
- b) a second transistor adapted to operate at a second current density so as to provide a second transistor output,
- c) a switched capacitor amplifier including a capacitor network, the amplifier providing an output based on the difference between the first and second transistor outputs,
- d) a capacitor shield adapted to shield said capacitor network, and
- e) a voltage driving circuit coupled to said capacitor shield, the voltage driving circuit being adapted to drive said shield to the voltage of one of the transistor outputs.
A switched capacitor bandgap reference circuit including an amplifier having a first capacitor coupled to its inverting input and a second capacitor provided in a feedback loop from the output to the inverting input, each of the capacitors being formed from a stack arrangement, the stack including first and second layers located one above the other and having a shield located thereabove, the circuit additionally including a first and a second bipolar transistor, the transistors adapted to operate at different current densities and being switchably coupled to the inverting and non-inverting inputs of the amplifier such that, in use, a switching operation effects the generation of a difference in base emitter voltage, ΔVeb, between the two transistors which when coupled to a base emitter voltage of the first transistor generates at the output of the amplifier a voltage reference, and wherein a voltage follower is additionally provided, the voltage follower being coupled to the shield of the capacitors and being further adapted to track voltage changes at the amplifier input, thereby bootstrapping the shield of the capacitors to the first transistor and minimizing the effect of parasitic capacitances.
A switched capacitor bandgap reference circuit including an amplifier having a first capacitor coupled to its inverting input and a second capacitor provided in a feedback loop from the output to the inverting input, the circuit additionally including a first and a second bipolar transistor, the transistors adapted to operate at different current densities and being switchably coupled to the inverting and non-inverting inputs of the amplifier such that, in use, a switching operation effects the generation of a difference in base emitter voltage, ΔVeb, between the two transistors which when coupled to a base emitter voltage of the first transistor generates at the output of the amplifier a voltage reference, the voltage reference being a combination of a proportional to absolute temperature (PTAT) voltage provided by the difference in base emitter voltages between the two transistors and a voltage provided by the base emitter voltage of the first transistor, the voltage provided by the base emitter voltage of the first transistor having first and second order contributions and wherein the circuit additionally comprises curvature correction components, the curvature correction components being coupled to the inverting input of the amplifier and adapted to provide a complimentary voltage to the second order contribution of the first transistor so as to compensate for any bow effect arising from the second order contribution.
Dependencies are inferred from the claim text.