Low-voltage comparator with wide input voltage swing
AssigneePhotobit Corporation
InventorAlexander I. Krymski
Life of this patent
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Abstract
A low voltage comparator for amplifying a voltage difference between a pair of differential inputs. A boost capacitor charges to a boost voltage in excess of the low supply voltage, a differential pair of MOSFET transistors, each said transistor including a gate, a source, a drain, and a body terminal. The comparator also includes a latch mechanism built from a cross-coupled pair of MOSFET transistors for latching the compared result. A well capacitor is used to charge the body terminal of the differential pair where the boost capacitor and the well capacitor boost the common source voltage and reduce the threshold voltage of the differential pair to allow the supply voltage to be at relatively low level.
Claims27
A low-voltage comparator for amplifying a voltage difference between a pair of differential inputs, the comparator comprising:
- a voltage source providing a voltage between first and second voltage levels;
- a differential pair of transistors, each of said transistors including a gate, a source, a drain, and a body terminal, said differential pair of transistors configured to enable an output to change based on the relationship between its two inputs,
- one of said transistors including a well capacitor that charges the body terminal of the differential pair;
- a boost capacitor configured to charge a common source node of said differential pair of transistors to a voltage above said first voltage level,
- wherein the boost capacitor and well capacitors boost said common source node thereby inducing a current through said differential pair.
A low-voltage comparator for amplifying a voltage difference between a pair of differential inputs, the comparator comprising:
- a power supply terminal, connected to receive a supply voltage;
- a boost capacitor that charges to a boost voltage based on said supply voltage;
- a differential pair of transistors having a common source terminal, each of said transistors including a gate, a source, a drain, and a body terminal;
- a cross-coupled pair of transistors, connected to reinforce a current flow in said differential pair of transistors;
- a well capacitor that charges said body terminal of the differential pair, said boost capacitor and well capacitor boosting a voltage at said common source terminal thereby inducing a current through said differential pair;
- and
- a plurality of switches which are switched to preset the comparator by grounding the source and the drain terminals of the differential pair and the cross-coupled pair of transistors.
A method of operating a comparator, comprising:
- obtaining two transistors which require a first voltage drop for forward biased operation;
- connecting said two transistors into a comparator, having input terminals which are connected to receive input voltages to be compared, and an output voltage indicating which of said input voltages has a higher level;
- obtaining a power supply voltage which has a lower voltage than said first voltage drop;
- and
- using a forward bias increase element to allow said two transistors to operate with said power supply voltage.
A comparator comprising:
- a supply voltage supplying a voltage between first and second voltage levels;
- a differential pair of transistors, each of said transistors having a gate, a source, a drain, and a body terminal, said differential pair configured to compare two input voltages at the gate terminals of said transistors, said source terminals of said transistors forming a common source terminal;
- a pulse receiving element configured to receive a pulse of said supply voltage having an amplitude of difference between the first and second voltage levels;
- a boost capacitor coupled to said common source terminal and said pulse receiving element, said boost capacitor charged to said first voltage level, said boost capacitor further charged when said pulse is received from said pulse receiving element, such that said common source terminal is boosted to approximately twice the first voltage level thereby inducing a current through said differential pair of transistors.
Dependencies are inferred from the claim text.