Common-mode feedback circuit
View Patent ↗A differential amplifier circuit with common-mode feedback is disclosed. The amplifier may include a first stage comprising a first differential input configured to drive a first differential pair transistor in a first differential current path, a second differential input configured to drive a second differential pair transistor in a second differential current path, a first differential output, and a second differential output, a second stage comprising a first differential input, a second differential input, a first differential output, and a second differential output, a common-mode feedback circuit, a first conducting element in a first common-mode current path parallel to the first differential current path and comprising a first conducting terminal coupled to the first differential output of the first stage, and a second conducting element in a second common-mode current path parallel to the second differential current path and comprising a first conducting terminal coupled to the second differential output of the first stage.
1. A differential amplifier circuit with common-mode feedback comprising:
a first stage comprising a first differential input configured to drive a first differential pair transistor in a first differential current path, a second differential input configured to drive a second differential pair transistor in a second differential current path, a first differential output, and a second differential output;
a second stage comprising a first differential input, a second differential input, a first differential output, and a second differential output; and
a common-mode feedback circuit configured to continuously drive a first conducting element in a conductive state and a second conducting element in a conductive state, the first conducting element in a first common-mode feedback current path parallel to the first differential current path and comprising a first conducting terminal coupled to the first differential output of the first stage, the second conducting element in a second common-mode feedback current path parallel to the second differential current path and comprising a first conducting terminal coupled to the second differential output of the first stage.
2. The amplifier of claim 1 , wherein:
the first conducting element comprises a second conducting terminal coupled to a high potential power supply; and
the second conducting element comprises a second conducting terminal coupled to a high potential power supply.
3. The amplifier of claim 2 , wherein the first conducting element comprises a PMOS transistor and the second conducting element comprises a PMOS transistor.
4. The amplifier of claim 2 , wherein the second stage comprises:
a first NMOS transistor comprising a gate configured to be driven by the first input of the second stage; and
a second NMOS transistor comprising a gate configured to be driven by the second input of the second stage.
5. The amplifier of claim 1 , wherein:
the first conducting element comprises a second conducting terminal coupled to a low potential power supply; and
the second conducting element comprises a second conducting terminal coupled to a low potential power supply.
6. The amplifier of claim 5 , wherein the first conducting element comprises a first NMOS transistor and the second conducting element comprises a first NMOS transistor.
7. The amplifier of claim 5 , wherein the second stage comprises:
a first PMOS transistor comprising a gate configured to be driven by the first input of the second stage; and
a second PMOS transistor comprising a gate configured to be driven by the second input of the second stage.
8. A method for providing common-mode feedback in a multi-stage amplifier, comprising:
generating a common-mode feedback signal based on a reference voltage and a common-mode value of a first differential output and a second differential output of an amplifier; and
driving continuously a first conducting element in a conductive state and a second conducting element in a conductive state with the common-mode feedback signal, the first conducting element in a first common-mode feedback current path parallel to a first differential current path in a first stage and comprising a first conducting terminal coupled to a first differential output of the first stage, the second conducting element in a second common-mode feedback current path parallel to a second differential current path in the first stage and comprising a first conducting terminal coupled to a second differential output of the first stage.
9. The method of claim 8 , wherein:
the first conducting element comprises a second conducting terminal coupled to a high potential power supply; and
the second conducting element comprises a second conducting terminal coupled to a high potential power supply.
10. The method of claim 9 , wherein the first conducting element comprises a PMOS transistor and the second conducting element comprises a PMOS transistor.
11. The method of claim 8 , wherein:
the first conducting element comprises a second conducting terminal coupled to a low potential power supply; and
the second conducting element comprises a second conducting terminal coupled to a low potential power supply.
12. The method of claim 11 , wherein the first conducting element comprises a first NMOS transistor and the second conducting element comprises a first NMOS transistor.