Amplifier with a MOS output stage
AssigneeSTMicroelectronics S.r.l.
InventorsFrederic Goutti, Vincent Rabary
Life of this patent
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Abstract
An amplifier including first, second, and third series-connected stages, the third stage including a MOS output transistor having its source or drain forming an output terminal of the amplifier, including means for detecting the transition from a first operating state of the output transistor in which the drain current varies little with the voltage between the drain and the source to a second state in which the drain current varies substantially proportionally to the voltage between the drain and the source; and means for, upon detection of such a transition, having the voltage gain of the amplifier and/or the product between the bandwidth of the amplifier and the voltage gain of the amplifier at the upper limit frequency of the bandwidth drop.
Claims20
An amplifier including first, second, and third series-connected stages, the third stage including a MOS output transistor having its source or drain forming an output terminal of the amplifier, the amplifier further including a first capacitance between the output terminal and the input of the second stage, and a second capacitance between the output terminal and the output of the second stage, the amplifier including:
- means for detecting the transition from a first operating state of the output transistor, in which the drain current varies little with the voltage between the drain and the source, to a second state, in which the drain current varies substantially proportionally to the voltage between the drain and the source;
- and
- means for, upon detection of such a transition, having the voltage gain of the amplifier and/or the product between the bandwidth of the amplifier and the voltage gain of the amplifier at the upper limit frequency of the bandwidth drop.
A method for protecting an amplifier including first, second, and third series-connected stages, the third stage including a MOS output transistor, having its source or its drain forming an output terminal of the amplifier, the amplifier further including a first capacitance between the output terminal and the input of the second stage, and a second capacitance between the output terminal and the output of the second stage, the method including the steps of:
- detecting the transition from a first operating state of the output transistor in which the drain current varies little with the voltage between the drain and the source to a second state in which the drain current varies substantially proportionally to the voltage between the drain and the source;
- and
- having, upon detection of such a transition, the voltage gain of the amplifier and/or the product between the bandwidth of the amplifier and the voltage gain of the amplifier at the upper limit frequency of the bandwidth drop.
An apparatus, comprising:
- an amplifier having an output transistor;
- and
- a circuit element coupled to the output transistor,
- wherein if the output transistor is in a first operating mode, the amplifier is coupled to operate independently of the circuit element, and
- wherein if the output transistor transitions from the first operating mode to a second operating mode, the circuit element is coupled to keep a cut-off frequency of the amplifier greater than a gain-bandwidth product (PGP) frequency of the amplifier.
A method for an amplifier, the method comprising:
- operating an output transistor of the amplifier in a first operating mode;
- transitioning operation of the output transistor from the first operating mode to a second operating mode;
- and
- in response to the transition, keeping a cut-off frequency of the amplifier greater than a-gain-bandwidth product (PGP) frequency of the amplifier.
Dependencies are inferred from the claim text.