Differential amplifier with common-mode regulating circuit
AssigneeSTMicroelectronics S.r.l.
InventorsGiancarlo Clerici, Luciano Tomasini
Life of this patent
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Abstract
A fully differential amplifier, in other words one having differential inputs and outputs, is associated with a circuit to regulate the output voltage reference. This circuit contains a resistive divider connected between the output terminals of the differential amplifier, a diode between the intermediate connection of the divider and common bases of load transistors of the differential amplifier, and a current mirror having a first branch connected to a reference voltage generator and a second branch which forms a current generator connected between the common bases of the load transistors and ground. This provides an efficient feedback control system with low power consumption and takes up less space on an integrated circuit.
Claims15
A differential amplifier circuit to regulate an output reference voltage, the differential amplifier circuit comprising
- two input transistors, each with a first terminal, a second terminal and a control terminal, and each having its first terminal connected to the first terminal of the other and, through a first current generator, to a first power supply terminal;
- two load transistors, each with a first terminal, a second terminal and a control terminal, and each having its control terminal connected to the control terminal of the other and, through a second current generator, to a second power supply terminal, and each of the load transistors having its first terminal connected to the second power supply terminal and its second terminal connected to the second terminal of one of the two input transistors;
- two input terminals, each connected to a corresponding control terminal of the two input transistors;
- two output terminals, each connected to a corresponding second terminal of one of the two input transistors;
- a resistive divider connected between the second terminals of the two input transistors;
- a unidirectionally conducting component connected between an intermediate connection of the resistive divider and the control terminals of the two load transistors;
- and
- a current mirror having a first branch connected to a constant reference voltage generator and a second branch comprising the second current generator.
A circuit coupled to a differential amplifier to regulate an output reference voltage, the circuit comprising:
- a current mirror circuit having a first branch connected to a reference voltage source structured to generate a reference voltage value and a second branch having a current generator;
- a diode connected to a first terminal of the current generator and to a midpoint of a resistive divider coupled across output terminals of the differential amplifier, wherein the current mirror circuit is structured to fix the output reference voltage at the reference voltage value.
A method to regulate an output reference voltage of a differential amplifier having load transistors coupled to its output terminals, the method comprising:
- providing a current mirror circuit having first and second circuit branches, wherein the second circuit branch is coupled to first terminals of the load transistors;
- providing a reference voltage value to the first branch of the current mirror circuit and generating a first current through the first branch;
- mirroring the first current with a second current in the second current branch;
- and
- if a mean common-mode voltage of the differential amplifier is greater than the reference voltage value, increasing current through the first terminals of the load transistors and correspondingly decreasing voltages at second terminals of the load transistors coupled to the output terminals of the differential amplifier to keep the output reference voltage fixed at the reference voltage value.
Dependencies are inferred from the claim text.