Complementary Current Reusing Preamp for Operational Amplifier

• US 20180316360A1
• Filed: 07/05/2018
• Published: 11/01/2018
• Est. Priority Date: 06/19/2014
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Hsieh, Tien-Ling
• Granted Patent: US 10,305,502 B2
• Time in Patent Office: Days
• CPC Class Codes: H03F 1/42 Modifications of amplifiers to extend the bandwidth
• CPC Class Codes: H03F 2200/36 the amplifier comprising means for increasing the bandwidth
• CPC Class Codes: H03F 2200/411 the output amplifying stage of an amplifier comprising two power stages
• CPC Class Codes: H03F 2203/45112 the biasing of the differential amplifier being controlled from the input or the output signal
• CPC Class Codes: H03F 2203/45116 Feedback coupled to the input of the differential amplifier
• CPC Class Codes: H03F 2203/45418 the CMCL comprising a resistor addition circuit
• CPC Class Codes: H03F 2203/45424 the CMCL comprising a comparator circuit
• CPC Class Codes: H03F 2203/45644 the LC comprising a cross coupling circuit, e.g. comprising two cross-coupled transistors
• CPC Class Codes: H03F 2203/45674 the LC comprising one current mirror
• CPC Class Codes: H03F 2203/45702 the LC comprising two resistors
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence
• CPC Class Codes: H03F 3/45237 Complementary long tailed pairs having parallel inputs and being supplied in series
• CPC Class Codes: H03F 3/45565 Controlling the active amplifying circuit of the differential amplifier
• CPC Class Codes: H03G 1/0029 using FETs
• CPC Class Codes: H03M 1/12 Analogue/digital converters H03M1/001 – H03M1/10 take precedence

Abstract

An apparatus includes a preamplifier stage to receive a power supply voltage and generate an output based upon an input. In particular, the preamplifier stage includes a biasing device coupled between the output and a ground node to bias a DC voltage level of the output independently of the power supply voltage. The preamplifier stage also includes a complementary circuit to receive the input and generate the output. The complementary circuit reuses a current through the preamplifier stage to provide an increased transconductance of the preamplifier stage for a given current level.

Claims

1. An apparatus comprising:

a preamplifier stage including;

an output;

a current source;

a PMOS differential pair coupled to a power supply side of the preamplifier stage, sources of the PMOS differential pair being coupled to the current source;

an NMOS differential pair coupled to a ground side of the preamplifier stage, drains of the NMOS differential pair being coupled to respective drains of the PMOS differential pair at the output; and

a biasing device coupled between the output and a ground node.

2. The apparatus of claim 1 wherein the preamplifier stage further comprises one or more short-channel devices to regulate the current through the preamplifier stage.

3. The apparatus of claim 1 wherein the biasing device comprises a diode-connected device.

4. The apparatus of claim 3 wherein the preamplifier stage further comprises a cross-coupled circuit coupled to the diode-connected device to adjust a gain of the preamplifier stage.

5. The apparatus of claim 3 wherein the preamplifier stage further comprises a resistive feedback circuit coupled to the diode-connected device to adjust a gain of the preamplifier stage.

6. The apparatus of claim 1 further comprising a feedback loop coupled to the preamplifier stage, the feedback loop to:

sense a DC voltage level of the output;

if the DC voltage level is above a predetermined threshold, reduce an amount of current injected to the preamplifier stage; and

if the DC voltage level is below a predetermined threshold, increase an amount of current injected into the preamplifier stage;

wherein the reduction in current injected results in a decrease of the DC voltage level of the output and the increase in current injected results in an increase of the DC voltage level.

7. The apparatus of claim 6 wherein the feedback loop controls a gate voltage of a short-channel device to vary the amount of current injected into the preamplifier stage.

8. The apparatus of claim 6 wherein the DC voltage level maintained by the feedback loop is substantially constant in varying thermal conditions.

9. A method comprising:

receiving, by a preamplifier stage, a power supply voltage and a differential input;

generating, by the preamplifier stage, an output based upon the differential input;

biasing a DC voltage level of the output independently of the power supply voltage; and

reusing, by a complimentary circuit, a current through the preamplifier stage, the complementary circuit including a PMOS differential pair coupled to a power supply side of the preamplifier stage, and an NMOS differential pair coupled to a ground side of the preamplifier stage, drains of the NMOS differential pair being coupled to respective drains of the PMOS differential pair at an output node of the preamplifier stage, sources of the PMOS differential pair being coupled to a current source.

10. The method of claim 9 wherein biasing further comprises biasing the DC voltage level with a diode-connected device.

11. The method of claim 10 further comprising adjusting a gain of the preamplifier stage using a cross-coupled circuit coupled to the diode-connected device.

12. The method of claim 10 further comprising adjusting a gain of the preamplifier stage using a resistive feedback circuit coupled to the diode-connected device.

13. The method of claim 9 further comprising regulating the current through the preamplifier stage using one or more short-channel devices.

14. The method of claim 9 further comprising:

sensing, by a feedback loop coupled to the preamplifier stage, the DC voltage level of the output;

if the DC voltage level is above a predetermined threshold, reducing, by the feedback loop, an amount of current injected to the preamplifier stage; and

if the DC voltage level is below a predetermined threshold, increasing, by the feedback loop, an amount of current injected into the preamplifier stage;

wherein reducing the current injected results in a decrease of the DC voltage level of the output and increasing the current injected results in an increase of the DC voltage level.

15. The method of claim 14 further comprising controlling, by the feedback loop, a gate voltage of a short-channel device to vary the amount of current injected into the preamplifier stage.

16. The method of claim 14 wherein the DC voltage level maintained by the feedback loop is substantially constant in varying thermal conditions.