Generation of a reference voltage

Abstract

A circuit of generation of a reference voltage by a first MOS transistor connected to a first terminal of application of a supply voltage, the first transistor being in series with a second MOS transistor controlled by an input stage of a transconductance amplifier and their junction point defining an output terminal providing the reference voltage, a first current source connecting the first supply terminal to a gate of the first transistor, a second current source connecting the second transistor to a second terminal of application of the supply voltage, at least one third MOS transistor connecting the two current sources, and a capacitive element directly connecting the output terminal to a conduction terminal of the third transistor to vary the conduction of this third transistor in case of a variation in output voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, previously described, very schematically shows in the form of blocks an analog-to-digital converter with differential inputs of the type to which the present invention applies as an example;

FIG. 2, previously described, shows an example of a voltage scale of the converter of FIG. 1;

FIG. 3, previously described, schematically shows a first conventional example of a follower assembly of generation of a reference voltage;

FIG. 4, previously described, shows a second conventional example of a follower assembly of generation of a reference voltage;

FIG. 5 shows a first embodiment of a circuit for generating a reference voltage according to the present invention;

FIG. 6 shows a second embodiment of a reference generation circuit according to the present invention; and

FIG. 7 is a partially detailed electric diagram of the circuit of FIG. 5.

Claims

1. A circuit of generation of a reference voltage by a first MOS transistor of a first channel type connected to a first terminal of application of a supply voltage, said first transistor being in series with a second MOS transistor of the same channel type controlled by an input stage of a transconductance amplifier, a junction point of the first and second transistors defining an output terminal providing the reference voltage, comprising: a first current source of fixed value connecting said first supply terminal to a gate of the first transistor;a second current source of fixed value connecting the second transistor to a second terminal of application of the supply voltage;at least one third MOS transistor of a second channel type connecting the first and second current sources; anda capacitive element directly connecting said output terminal to a conduction terminal of the third transistor to vary the conduction of this third transistor in case of a variation in the output voltage.

2. The circuit of claim 1, wherein the third transistor directly connects the gate of the first transistor to the second current sources, said capacitive element being in parallel on the second transistor.

3. The circuit of claim 1, wherein a fourth transistor of the second channel type is interposed between the third transistor and the second current source, said capacitive element connecting said output terminal to the junction point of the third and fourth transistors.

4. The circuit of claim 1, wherein the circuit is formed with at least two types of transistors which differentiate by their respective gate oxide thicknesses, the first and third transistors being formed with a relatively thin gate oxide with respect to the second transistor.

5. The circuit of claims 3, wherein the fourth transistor comprises a relatively thick gate oxide.

6. The circuit of claim 1, wherein the first transistor is sized according to the current capable of being sourced or sunk by the circuits connected to the output terminal.

7. The circuit of claim 1, wherein the second transistor is sized according to the fixed value of the current sources.

8. The circuit of claim 1, wherein the second current source is formed of a MOS transistor of the second type biased by a fixed signal.

9. The circuit of claim 8, wherein the first current source comprises a MOS transistor of the first type.

10. The circuit of claim 1, for generating a voltage closer to that of the first terminal than to that of the second terminal, wherein the first and second channel types are respectively P and N.

11. The circuit of claim 1, for generating a voltage closer to that of the second terminal than to that of the first terminal, wherein the first and second channel types are respectively N and P.