US 6,806,744 B1Granted

High speed low voltage differential to rail-to-rail single ended converter

AssigneeNational Semiconductor Corporation

InventorsMarshall J. Bell, David B. Cooper, James Kozisek

Life of this patent

Estimating the term…

Loading patent…

Abstract

A method and system is arranged to convert a differential low-voltage input signal (e.g. LVDS or RSDS) into a single-ended output signal. An operational trans-conductance amplifier (OTA) is configured to convert the input signal into a current. A trans-impedance stage is configured to convert the current into the single-ended output signal. The voltage associated with the output of the OTA corresponds to approximately VDD/2. The trans-impedance stage comprises an inverter circuit, a p-type transistor, and an n-type transistor. The transistors are arranged in a negative feedback configuration with the inverter. The single-ended output signal has a voltage swing that approximately corresponds to the sum of the VGS of the n-type transistor and the VGS of the p-type transistor. The output signal may be buffered by additional circuits such as an inverter, a Schmitt, as well as others.

Claims20

Dependent claims

An apparatus for converting a differential signal to a single-ended output signal, wherein the apparatus is operated from first and second power supplies, the apparatus comprising:

a differential pair circuit that is configured to provide an intermediate signal in response to the differential signal;
a current mirror circuit that is coupled to the differential pair circuit such that the current mirror circuit is a load for the differential pair circuit, wherein the current mirror circuit is arranged such that a voltage associated with the intermediate signal approximately corresponds to an arithmetic mean of the first power supply voltage and the second power supply voltage;
and
a first current source circuit that is coupled to the differential pair circuit such that the first current source provides a tail current to the differential pair circuit;
and
a trans-impedance circuit that is configured to operate from the first power supply voltage and the second power supply voltage, wherein the trans-impedance stage comprises:
a first inverter circuit having a first inverter input and a first inverter output, wherein the first inverter input is configured to receive the intermediate signal and the first inverter output is configured to provide an output signal that is responsive to the intermediate signal;
a first transistor having a first gate, a first drain, and a first source, wherein the first gate is coupled to the first inverter output, the first drain is coupled to the first power supply, and the first source is coupled to the first inverter input, and
a second transistor having a second gate, a second drain, and a second source, wherein the second gate is coupled to the first inverter output, the second drain is coupled to the second power supply, and the second source is coupled to the first inverter input.

6 more elements

An apparatus for converting a differential signal to a single-ended output signal, wherein the apparatus is operated from first and second power supplies, the apparatus comprising:

an operational trans-conductance amplifier having an amplifier input and an amplifier output, wherein:
the operational trans-conductance amplifier is configured to operate from the first power supply and the second power supply, the amplifier input is arranged to receive the differential signal, and the amplifier output is arranged to provide an intermediate signal that is responsive to the differential signal;
and
a trans-impedance stage that is configured to operate from the first and second power supplies, wherein the trans-impedance stage is arranged in cooperation with the operational trans-conductance amplifier such that a voltage associated with the intermediate signal approximately corresponds to an arithmetic mean of the first and second power supplies, wherein the trans-impedance stage comprises:
a first inverter circuit having a first inverter input that is coupled to the amplifier output, and a first inverter output that is configured to provide an output signal that is responsive to the intermediate signal;
a first transistor having a first gate that is coupled to the output signal, a first drain that is coupled to the first power supply, and a first source that is coupled to the first inverter input;
and
a second transistor having a second gate that is coupled to the output signal, a second drain that is coupled to the second power supply, and a second source that is coupled to the first inverter input.

5 more elements

An apparatus for converting a differential signal to a single-ended output signal, wherein the apparatus is operated from first and second power supplies, the apparatus comprising:

an operational trans-conductance means that is configured to provide a current to an intermediate node in response to the differential signal;
and
a trans-impedance means that is configured to provide an output voltage in response to the current such that the output voltage corresponds to:
a sum of a voltage level and a gate-to-source voltage of a first transistor when the current has a negative polarity, a difference of the voltage level and a gate-to-source voltage of a second transistor when the current has a positive polarity, wherein the operational trans-conductance amplifier and the trans-impedance means are arranged in cooperation with one another such that a voltage associated with the intermediate node approximately corresponds to a mid-supply voltage.

1 more element

Dependencies are inferred from the claim text.