Low voltage fully differential operational amplifier with improved common mode circuitry
AssigneeAdvanced Micro Devices, Inc.
InventorGeoffrey E. Brehmer
Life of this patent
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Abstract
A fully differential operational amplifier with improved common mode circuitry for low supply voltage applications is disclosed. The amplifier includes inventing and non-inventing inputs and dual-ended invented and non-invented outputs. The amplifier also includes source transistors for pulling the output to obtain particular output voltage swing. Connections between the inputs and outputs include DC biasing circuitry. The amplifier includes a transistor of select size and characteristics to compensate for voltage drop due to other transistors of the amplifier. Common mode circuitry of the amplifier provides a high level of common mode reconstruction.
Claims25
A fully differential operational amplifier, comprising:
- an inverting input;
- a non-inverting input;
- a first output, having a first voltage;
- a second output, having a second voltage;
- a reference voltage input, having a reference voltage;
- first circuitry for amplifying, connected to said inverting input and said non-inverting input to yield said first output and said second output, and including at least one pair of MOS-type transistors for pushing and pulling;
- second circuitry, including at least one pair of MOS-type transistors for pushing and pulling, for common mode reconstruction, each of the MOS-type transistors having an associated V.sub.ds that is equal to or a multiple of each V.sub.ds of the other MOS-type transistors, said second circuitry receives said reference voltage input and said first output and said second output and pushes or pulls each of said first output and said second output to draw said first voltage and said second voltage substantially near said reference voltage of said reference voltage input.
In a method of DC biasing and common mode reconstructing in a fully differential operational amplifier having common mode circuitry, dual inputs and dual-ended outputs, the improvement wherein said DC biasing includes pushing said output high when a voltage differential between said dual inputs is positive to bring the voltage level of said outputs near a power supply voltage and pulling low when said voltage differential between said dual inputs is negative to bring the voltage level of said outputs near a ground, and wherein said common mode reconstructing includes inputting an externally supplied analog ground reference voltage of about a mid-point of a range of power supply voltage and inputting an average of said outputs from said amplifier and substantially mirroring currents of said common mode circuitry using at least one pair of transistors having a V.sub.ds that is common or related as a multiple in order to reconstruct said outputs to account for voltage errors attributable to common mode signals input to said amplifier via said inputs and due to voltage drop attributable thereto within said amplifier, and providing amplifier circuitry having substantially mirrored currents using transistors each with a V.sub.ds that is the same or a multiple of the V.sub.ds of the transistors of said at least one pair.
A method of common mode reconstruction in a differential operational amplifier having dual inputs and dual-ended outputs, said amplifier comprised of sinking transistors and sourcing transistors and corresponding biasing transistors, comprising the steps of:
- inputting an externally supplied analog ground reference voltage of about a mid-point of a range of power supply voltage for said amplifier to a gate of a first p-channel transistors;
- inputting an average signal being an average of said outputs;
- from said amplifier to a gate of a second p-channel transistor;
- coupling each of said first p-channel transistor and said second p-channel transistor to series connected p-channel transistors;
- and
- connecting said first p-channel transistor to series connected n-channel transistors, at least two of said n-channel transistors having a common gate;
- connecting said second p-channel transistor to series connected n-channel transistors, each of said n-channel transistors having a common gate;
- connecting each of said series connected n-channel transistors to a common ground;
- and
- connecting said amplifier at a drain of said first p-channel transistor;
- wherein currents in said amplifier are substantially mirrored via said method, thereby reconstructing said dual-ended outputs to account for voltage errors attributable to common mode signals input to said amplifier via said inputs and due to voltage drop attributable to said amplifier.
A fully differential operational amplifier, comprising:
- an amplifier section including an inverting input, a non-inverting input, a first output, and a second output;
- a DC biasing network coupled to the amplifier section and having first, second, third, and fourth cascode arrangements and configured to provide first, second, third, and fourth bias voltages to the amplifier;
- a common mode circuit section coupled to the DC biasing network and to the amplifier section, and arranged to receive the first bias voltage, a reference voltage, and a midpoint voltage, the midpoint voltage relative to voltages of the first and second outputs, the common mode circuit section including a fifth cascode arrangement configured to receive a current generated from the reference voltage, and a sixth cascode arrangement configured to receive a current generated from the midpoint voltage, and the fifth cascode arrangement configured to provide a bias voltage to sinking transistors of the amplifier.
Dependencies are inferred from the claim text.