Active load with adjustable common-mode level
First Claim
1. A differential amplifier, comprising:
- a first stage configured to receive a differential input signal; and
a second stage, coupled to an output of the first stage, including;
an active load having a transistor pair that provides a differential output signal at respective output terminals of the active load; and
a bias circuit that provides bias voltages to the transistor pair in the active load, and configured to provide an adjustable common-mode voltage at respective output terminals of the active load.
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Accused Products
Abstract
A differential preamplifier includes an active load with adjustable common-mode output level. The active load includes a transistor pair, a resistor pair, and a current source. The transistor load is employed to provide high gain, low offset, and a large bandwidth for the differential preamplifier. The resistor pair and current source are used to increase the common-mode output level of the differential preamplifier and to bias the transistor load. The current source can be varied to provide an adjustable common-mode output level suitable for driving next stage devices. The active load design allows the differential preamplifier to operate using only low power voltage supplies and with small-sized transistors.
11 Citations
30 Claims
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1. A differential amplifier, comprising:
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a first stage configured to receive a differential input signal; and a second stage, coupled to an output of the first stage, including; an active load having a transistor pair that provides a differential output signal at respective output terminals of the active load; and a bias circuit that provides bias voltages to the transistor pair in the active load, and configured to provide an adjustable common-mode voltage at respective output terminals of the active load. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A differential amplifier, comprising:
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a first transistor pair configured to receive a differential input signal; and an active load, coupled to the first transistor pair, including; a second transistor pair that provides a differential output signal at respective output terminals of the active load; and a bias circuit that provides bias voltages to the second transistor pair, and configured to provide an adjustable common-mode voltage at respective output terminals of the active load. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. In a differential amplifier having an active load, the active load including a first resistor coupled between a common node and a first output terminal of the active load and a second resistor coupled between the common node and a second output terminal of the active load, a method of providing an adjustable common-mode voltage at the respective output terminals of the active load, the method comprising the steps of:
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(a) biasing the active load using a current source coupled to the active load at the common node; and (b) adjusting the current source to provide desired voltage drops across the first and second resistors, wherein respective voltage drops across the first and second resistors provide the adjustable common-mode voltage at the output terminals of the active load. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
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24. A two stage differential amplifier having active loads with adjustable common-mode output voltages, comprising:
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a differential amplifier input and a differential amplifier output; a first differential amplifier stage including a first transistor pair, respective sources of the first transistor pair connected to a first current supply, respective gates of the first transistor pair connected to the differential amplifier input, respective drains of the first transistor pair connected to a first active load; a second differential amplifier stage including a second transistor pair, respective sources of the second transistor pair connected to a second current supply, respective gates of the second transistor pair connected to the respective drains of the first transistor pair and forming a first differential amplifier stage output, respective drains of the second transistor pair connected to a second active load; and a feedback resistor pair connecting the respective gates of the second transistor pair to the respective drains of the second transistor pair; wherein; the first active load includes a third transistor pair and a first active load resistor pair, respective sources of the third transistor pair connected to a first supply voltage, respective drains of the third transistor pair connected to the respective drains of the first transistor pair, respective gates of the third transistor pair connected to a third current source, the first active load resistor pair connecting the respective gates of the third transistor pair to the respective drains of the third transistor pair; the second active load includes a fourth transistor pair and a second active load resistor pair, respective sources of the fourth transistor pair connected to a second supply voltage, respective drains of the fourth transistor pair connected to the respective drains of the second transistor pair, respective gates of the fourth transistor pair connected to a fourth current source, the second active load resistor pair connecting the respective gates of the fourth transistor pair to the respective drains of the fourth transistor pair; and the differential amplifier output is taken from the drains of the fourth transistor pair. - View Dependent Claims (25, 26, 27, 28, 29)
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30. A differential amplifier having an active load with adjustable common-mode output voltage, comprising:
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a differential amplifier input and a differential amplifier output; and a first transistor pair, respective sources of the first transistor pair connected to a first current supply, respective gates of the first transistor pair connected to the differential amplifier input, respective drains of the first transistor pair connected to an active load; wherein; the active load includes a second transistor pair and an active load resistor pair, respective sources of the second transistor pair connected to a first supply voltage, respective drains of the second transistor pair connected to the respective drains of the first transistor pair, respective gates of the second transistor pair connected to a second current source, the active load resistor pair connecting the respective gates of the second transistor pair to the respective drains of the second transistor pair; and the differential amplifier output is taken from the drains of the second transistor pair.
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Specification