Reference buffer with wide trim range

Patent metadata

Field	Value
Publication number	US-9397682-B2
Application number	US-201414262274-A
Country	US
Kind code	B2
Filing date	Apr 25, 2014
Priority date	Apr 25, 2014
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

Circuits for generating voltage references are common in electronics. For example, these circuits are used in analog-to-digital converters, which convert an analog signal into its digital representation by comparing analog input signals against one or more voltage references provided by those circuits. In many applications, the speed and accuracy of such voltage references are very important. The speed of the voltage references is related to the physical properties of the devices in the circuit. The accuracy of the voltage reference is directly related to the circuit's ability to trim the full-scale voltage output. The present disclosure describes a fast and efficient reference buffer with a wide trim range which is particular suitable for submicron processes and high speed applications. The reference buffer comprises a plurality of diode-connected transistors, which can be selected to turn on or off using a controller to provide a wide trim range.

First claim

What is claimed is:

1. A programmable reference buffer comprising:
a stacked source follower comprising a first transistor and a second transistor in a common drain configuration;
a pass device separating the first transistor and a second transistor, wherein the pass device comprises selectable diode-connected transistors and switches corresponding to the selectable diode-connected transistors, wherein each switch is connected between a gate of a corresponding selectable diode-connected transistor and a drain of the corresponding selectable diode-connected transistor; and
a controller having output control signals for controlling the switches to select one or more ones of the selectable diode-connected transistors to be used as part of the pass device based on a reference voltage to be provided at a first terminal and a second terminal of the pass device.

2. The programmable reference buffer of claim 1 , wherein the one or more ones of the selectable diode-connected transistors comprises selectable diode-connected transistors having different threshold voltages for providing different reference voltage trim ranges.

3. The programmable reference buffer of claim 2 , wherein the selectable diode-connected transistors associated with different threshold voltages are at least in part provided by selectable diode-connected transistors having different widths.

4. The programmable reference buffer of claim 3 , wherein different reference voltage trim ranges comprises different ranges of reference voltage which corresponding selectable diode-connected transistors are configured to maintain at the first terminal and the second terminal of the pass device for substantially the same bias current through the pass device.

5. The programmable reference buffer of claim 2 , wherein the selectable diode-connected transistors with different threshold voltages are in part provided by selectable diode-connected transistors whose threshold voltages are affected by one or more of the following: body effect, channel length, stress, well proximity effect, and gate bias.

6. The programmable reference buffer of claim 1 , wherein:
the selectable diode-connected transistors comprises selectable groups of diode-connected transistor(s) associated with different reference voltage trim ranges; and
the controller selects one or more ones of the selectable diode-connected transistors based on the reference voltage to be provided by determining in which of the different reference voltage trim ranges the reference voltage to be provided falls and outputting control signals to select a selectable group of diode-connected transistor(s) corresponding to the determined reference voltage trim range.

7. The programmable reference buffer of claim 6 , wherein the selectable groups of diode connected transistor(s) associated with different threshold voltages comprises groups of one or more diode-connected transistors in parallel.

8. The programmable reference buffer of claim 7 , wherein the one or more selectable diode-connected transistors in parallel have substantially the same width.

9. The programmable reference buffer of claim 7 , wherein the switches corresponding to the selectable diode-connected transistors are not in the signal path of the selectable diode-connected transistors.

10. The programmable reference buffer of claim 1 , wherein:
the control signals from the controller closes one or more ones of pull down switches corresponding to selectable diode-connected transistors to operate one or more ones of the selectable diode-connected transistors not selected to be used as part of the pass device in a cut-off region.

11. The programmable reference buffer of claim 10 , wherein each one of the pull down switches is provided between a gate of a corresponding selectable diode-connected transistor and a bias voltage.

12. The programmable reference buffer of claim 1 , wherein the selectable diode-connected transistors comprises one or more of the following: selectable diode-connected n-channel metal-oxide-semiconductor field-effect transistor(s) and selectable diode-connected p-channel metal-oxide semiconductor field-effect transistor(s).

13. The programmable reference buffer of claim 1 , wherein the first transistor is an n-channel metal-oxide-semiconductor field-effect transistor and the second transistor is a p-channel metal-oxide-semiconductor field-effect transistor.

14. The programmable reference buffer of claim 1 , wherein
the first terminal of the pass device is connected to the source of the first transistor; and
the second terminal of the pass device is connected to the source of the second transistor.

15. A floating voltage source as a battery having a positive terminal and a negative terminal, the voltage source comprising:
a stacked source follower comprising a first transistor and a second transistor in a common drain configuration;
a pass device separating the first transistor and a second transistor, wherein the pass device comprises selectable diode-connected transistors and switches for selecting corresponding selectable diode-connected transistors, wherein each one of the switches is connected between a gate of a corresponding selectable diode-connected transistor and a drain of the corresponding selectable diode-connected transistor; and
a controller having output control signals for closing one or more ones of the switches to select one or more corresponding ones of the selectable diode-connected transistors to be used as part of the pass device based on a voltage to be provided at a first terminal and a second terminal of the pass device;
wherein the first terminal of the pass device is the positive terminal of the battery, and the second terminal of the pass device is the negative terminal of the battery.

16. A method for providing a range of reference voltages, the method comprising:
outputting control signals, by a controller, based on a reference voltage to be provided by a pass device, wherein the pass device comprises selectable diode-connected transistors and switches corresponding to selectable diode-connected transistors, each one of the switches is connected between a gate of a corresponding selectable transistor and a drain of the corresponding selectable diode-connected transistor, the pass device separates a first transistor and a second transistor, and the first transistor and the second transistor make up a stack source follower in a common drain configuration;
closing, using the control signals, one or more ones of the switches, to select one or more corresponding ones of the selectable diode-connected transistors of the pass device to be used as part of the pass device; and
outputting, by the pass device, the reference voltage at a first terminal and a second terminal of the pass device.

17. The method of claim 16 , wherein:
the selectable diode-connected transistors comprises selectable groups of diode-connected transistor(s) associated with different reference voltage trim ranges; and
the method further comprises determining in which of the different reference voltage trim ranges the reference voltage to be provided falls; and
closing the one or more ones switches selects a selectable group of diode-connected transistor(s) corresponding to the determined reference voltage trim range to be used as part of the pass device.

18. The method of claim 16 , wherein:
the switches are not in the signal path of the selectable diode-connected transistors.

19. The method of claim 16 , further comprising:
outputting further control

Assignees

• Analog Devices Inc

Inventors

• Dinc Huseyin
• Ali Ahmed Mohamed Abdelatty

Classifications

• H03M1/164

  the steps being performed sequentially in series-connected stages (H03M1/161 takes precedence) · CPC title

• H03F3/505 Primary

  with field-effect devices · CPC title

• H03M1/167

  all stages comprising simultaneous converters (H03M1/165 takes precedence) · CPC title

• H03K19/018585

  programmable · CPC title

• H03M1/38

  sequentially only, e.g. successive approximation type (converting more than one bit per step H03M1/14) · CPC title