Fast current mode sigma-delta analog-to-digital converter

Patent metadata

Field	Value
Publication number	US-10128866-B2
Application number	US-201514885047-A
Country	US
Kind code	B2
Filing date	Oct 16, 2015
Priority date	Oct 16, 2015
Publication date	Nov 13, 2018
Grant date	Nov 13, 2018

Abstract

A current mode sigma-delta modulator comprises an input node; a comparator that compares a voltage of the input node to a reference voltage and outputs a comparison result; an integrating capacitor connected to an input of the comparator; and a switched capacitor circuit connected at a first end to the input node, the input of the comparator, and the integrating capacitor, and connected at a second end to an output of the comparator. The current mode sigma-delta modulator is a component of an analog-to-digital converter.

First claim

What is claimed is:

1. A current mode sigma-delta modulator, comprising:
an input node;
a comparator configured to compare a voltage of the input node to a reference voltage and to output a comparison result;
an integrating capacitor connected to an input of the comparator; and
a switched capacitor circuit connected at a first end to the input node, the input of the comparator, and the integrating capacitor, and connected at a second end to an output of the comparator,
wherein the switched capacitor circuit includes:
a switched capacitor having a first electrode and a second electrode, the second electrode connected to a predetermined voltage;
a first switch directly connected to the first electrode of the switched capacitor and the input node so as to selectively allow a charge to flow therebetween; and
a second switch connected between the predetermined voltage and the first electrode of the switched capacitor.

2. The current mode sigma-delta modulator according to claim 1 , wherein the first switch is controlled by a signal corresponding to the output of the comparator.

3. The current mode sigma-delta modulator according to claim 1 , wherein the second switch is controlled by a signal corresponding to an inverse of the output of the comparator.

4. The current mode sigma-delta modulator according to claim 1 , wherein the first switch is a first transistor and the second switch is a second transistor.

5. The current mode sigma-delta modulator according to claim 1 , wherein
in a case where the output of the comparator is at a high level of two possible levels, the first switch is closed and the second switch is opened, and
in a case where the output of the comparator is at a low level of the two possible levels, the first switch is opened and the second switch is closed.

6. A solid-state imaging device, comprising:
a pixel circuit configured to convert an incident light into an analog signal;
the current mode sigma-delta modulator according to claim 1 ; and
a vertical signal line configured to conduct the analog signal to the input node of the current mode sigma-delta modulator.

7. An analog-to-digital converter, comprising:
the current mode sigma-delta modulator according to claim 1 ; and
a decimation filter configured to receive the output of the comparator and output a value corresponding to a digital representation of an analog signal received at the input node.

8. A method of operating a current mode sigma-delta modulator, comprising:
inputting a voltage at an input node;
comparing the voltage of the input node to a reference voltage with a comparator, and outputting a comparison result; and
providing an output of the comparator to an integrating capacitor that is connected to an input of the comparator and the input node, by way of a switched capacitor circuit connected at a first end to the input node, the input of the comparator, and the integrating capacitor and at a second end to an output of the comparator,
wherein the switched capacitor circuit includes:
a switched capacitor having a first electrode and a second electrode, the second electrode connected to a predetermined voltage;
a first switch directly connected to the first electrode of the switched capacitor and the input node so as to selectively allow a charge to flow therebetween; and
a second switch connected between the predetermined voltage and the first electrode of the switched capacitor.

9. A current mode sigma-delta modulator, comprising:
an input node;
an transconductance amplifier configured to input a voltage of the input node and a reference voltage to output a signal;
a first integrating capacitor connected to an input of the transconductance amplifier;
a comparator configured to compare an output of the transconductance amplifier to the reference voltage and to output a comparison result;
a second integrating capacitor connected to an input of the comparator;
a first switched capacitor circuit connected at a first end to the input node, the input of the transconductance amplifier, and the first integrating capacitor, and connected at a second end to an output of the comparator; and
a second switched capacitor circuit connected at a first end to the output of the transconductance amplifier, the input of the comparator, and the second integrating capacitor, and connected at a second end to the output of the comparator,
wherein the first switched capacitor circuit includes:
a first switched capacitor having a first electrode and a second electrode, the second electrode being connected to a predetermined voltage,
a first switch directly connected to the first electrode of the first switched capacitor and the input node so as to selectively allow a charge to flow therebetween, and p 2 a second switch connected between the predetermined voltage and the first electrode of the first switched capacitor.

10. The current mode sigma-delta modulator according to claim 9 , wherein the second switched capacitor circuit comprises:
a second switched capacitor having a first electrode and a second electrode, the second electrode being connected to the predetermined voltage,
a third switch connected between the first electrode of the second switched capacitor and an output node of the transconductance amplifier, and
a fourth switch connected between the predetermined voltage and the first electrode of the second switched capacitor.

11. The current mode sigma-delta modulator according to claim 10 , wherein the first switch and the third switch are controlled by a signal corresponding to the output of the comparator.

12. The current mode sigma-delta modulator according to claim 10 , wherein the second switch and the fourth switch are controlled by a signal corresponding to an inverse of the output of the comparator.

13. The current mode sigma-delta modulator according to claim 10 , wherein the first switch is a first transistor, the second switch is a second transistor, the third switch is a third transistor, and the fourth switch is a fourth transistor.

14. The current mode sigma-delta modulator according to claim 10 , wherein
in a case where the output of the comparator is at a high level of two possible levels, the first and third switches are closed and the second and fourth switches are opened, and
in a case where the output of the comparator is at a low level of the two possible levels, the first and third switches are opened and the second and fourth switches are closed.

15. The current mode sigma-delta modulator according to claim 10 , further comprising a replica current source connected to the second integrating capacitor.

16. The current mode sigma-delta modulator according to claim 15 , wherein a current value of the replica current source is equal to a current value of the input node times a ratio of a capacitance of the second switched capacitor to a capacitance of the first switched capacitor.

17. The current mode sigma-delta modulator according to claim 9 , further comprising a replica current source connected to the second switched capacitor circuit.

18. A solid-state imaging device, comprising:
a pixel circuit configured to convert an incident light into an analog signal;
the current mode sigma-delta modulator according to claim 9 ; and
a vertical signal line configured to conduct the analog signal to the input node of the current mode sigma-delta modulator.

19. A solid-state imaging device, comprising:
a pixel circuit configured to convert an incident light into an analog signal;
the current m

Assignees

• Sony Semiconductor Solutions Corp

Inventors

• Tkachev Vadim

Classifications

• H04N23/54

  Mounting of pick-up tubes, electronic image sensors, deviation or focusing coils · CPC title

• H03M3/456

  the modulator having a first order loop filter in the feedforward path · CPC title

• H04N5/2253

  Electricity · mapped topic

• H03M3/462

  Details relating to the decimation process (decimation filters in general H03H17/0416, H03H17/0621) · CPC title

• H03M3/454

  with distributed feedback, i.e. with feedback paths from the quantiser output to more than one filter stage · CPC title