Analog rail-to-rail comparator with hysteresis
AssigneeAtmel Corporation
InventorsArmin Prohaska, Holger Vogelmann
Life of this patent
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Abstract
According to a novel aspect, operating an analog rail-to-rail comparator circuit with common mode detection of differential input signals includes generating a hysteresis current for the comparator circuit based on a common mode voltage used for the common mode detection. The hysteresis current is added to a differential output of a comparator in the comparator circuit, such that a hysteresis voltage at an output of the comparator circuit is substantially independent of the common mode voltage.
Claims20
A method of operating an analog rail-to-rail comparator circuit with common mode detection of differential input signals, the method comprising:
- providing, as outputs from a comparator, first, second, third and fourth differential signals when a common mode voltage used for the common mode detection is between zero volts and a supply voltage of the comparator circuit;
- generating a hysteresis current for the comparator circuit based on the common mode voltage;
- and
- adding the hysteresis current to a one of the differential outputs of the comparator in the comparator circuit, such that a hysteresis voltage at an output of the comparator circuit is substantially independent of the common mode voltage,
- wherein generating a hysteresis current includes:
- providing an output of a PMOS differential stage current source to a first current mirror having an output,
- providing an output of a NMOS differential stage current source to a second current mirror via a node, wherein the NMOS differential stage current source has an output,
- providing the output of the first current mirror to the node, and
- obtaining the hysteresis current from the output of the second current mirror.
A comparator circuit comprising:
- a comparator operable to provide common mode detection of differential input signals based on a common mode voltage and to generate first, second, third and fourth differential output signals when the common mode voltage is between zero volts and a supply voltage for the comparator circuit;
- output stage circuitry operable to convert the differential output signals to a corresponding digital signal;
- circuitry operable to add a hysteresis current to a selected one of the differential output signals such that a hysteresis voltage at an output of the comparator circuit is substantially independent of the common mode voltage, wherein the circuitry to add the hysteresis current includes:
- a PMOS differential stage current source coupled to a first current mirror having an output, and
- a NMOS differential stage current source coupled at a node to a second current mirror having an output,
- the output of the first current mirror being coupled to the node, and
- the hysteresis current being provided from the output of the second current mirror.
The comparator circuit 12 wherein a signal from the output stage circuitry controls one of the switches and an inverted version of the signal from the output stage circuitry controls the other one of the switches.
An integrated circuit comprising:
- a comparator operable to provide common mode detection of differential input signals based on a common mode voltage and to generate first, second, third and fourth differential output signals when the common mode voltage is between zero volts and a supply voltage for the comparator circuit, wherein if the common mode voltage is equal to zero volts, then only the first and second differential output signals are provided as output of the comparator, and wherein if the common mode voltage is equal to the supply voltage then only the third and fourth differential output signals are provided as output of the comparator, the sum of the first and second differential output signals being substantially constant, and the sum of the third and fourth differential output signals being substantially constant;
- output stage circuitry operable to convert the differential output signals to a corresponding digital signal;
- a current source to add a hysteresis current to a selected one of the differential output signals, wherein the current source comprises:
- a PMOS differential stage current source coupled between a supply voltage and a first current mirror having an output, the PMOS differential stage current source being controlled by the common mode voltage, and
- an NMOS differential stage current source coupled between ground and a node that is coupled to a second current mirror having an output, the NMOS differential stage current source being controlled by the common mode voltage,
- the output of the first current mirror being coupled to the node, and
- the hysteresis current being provided from the output of the second current mirror.
Dependencies are inferred from the claim text.