Circuit and a method for controlling the bias current in a switched capacitor circuit
AssigneeAdvanced Micro Devices, Inc.
InventorsRolf Jaehne, Lutz Dathe, Andreas Huschka
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Abstract
A tunable constant GM circuit allows to compensate for temperature and process variations with high precision by correspondingly adjusting a resistance value and/or the ratio of transistor widths. Thus, in switched capacitor circuits the frequency behaviour, such as the settling time, may be controlled by providing a compensated bias to the transconductance amplifiers typically used in these circuits.
Claims21
A bias current circuit for a transconductance amplifier having two input transistors with a predefined design length, the bias circuit comprising:
- a constant transconductance circuit including:
- a first and a second transistor having substantially the same design length than said input transistors, the second transistor having a transistor width greater than the first transistor;
- a regulation circuit configured to flow substantially identical currents through said first and second transistors and output a bias current for said transconductance amplifier;
- and
- a tunable resistor block connected to the source of the second transistor.
A bias current circuit for a transconductance amplifier having two input transistors with a predefined design length, the bias circuit comprising:
- a constant transconductance circuit including:
- a regulation circuit configured to output a bias current for said transconductance amplifier;
- at least one first and a plurality of second transistors, wherein said plurality of second transistors are arranged to be selectively connectible in parallel to each other, and a resistor arranged in a common source line of said second transistors connected in parallel.
An integrated switched capacitor circuit comprising:
- a transconductance amplifier;
- a plurality of capacitors connected to said transconductance amplifier, at least one of the capacitors being switchable;
- an RC tuning circuit configured to determine an RC time constant in said switched capacitor circuit and to switch said at least some of the capacitors on the basis of the determined RC time constant;
- and
- a tunable constant transconductance circuit configured to provide a bias to said transconductance amplifier on the basis of the determined RC time constant.
A method of tuning the frequency behaviour of a transconductance amplifier in an integrated circuit, the method comprising:
- obtaining a signal indicative of an RC time constant associated with said integrated circuit, and
- adjusting at least one of a resistance value and a ratio of transistor widths in a constant transconductance circuit in response to said signal to adjust a bias current supplied to said transconductance amplifier.
Dependencies are inferred from the claim text.