ANALOG-DIGITAL CONVERSION CIRCUIT, SENSOR APPARATUS, CELLULAR PHONE, AND DIGITAL CAMERA

• US 20150192664A1
• Filed: 06/10/2013
• Published: 07/09/2015
• Est. Priority Date: 09/14/2012
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Sato, Hideki, Inoue, Takahiro
• Granted Patent: US 9,285,465 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 7/4861 Circuits for detection, sampling, integration or read-out
• CPC Class Codes: H03M 1/0607 Offset or drift compensation removal of offset already present on the analogue input signal H03M1/1295
• CPC Class Codes: H03M 1/12 Analogue/digital converters H03M1/001 – H03M1/10 take precedence
• CPC Class Codes: H03M 1/181 in feedback mode, i.e. by determining the range to be selected from one or more previous digital output values
• CPC Class Codes: H03M 1/368 having a single comparator per bit, e.g. of the folding type
• CPC Class Codes: H03M 1/52 Input signal integrated with linear return to datum

Abstract

An analog-digital conversion circuit (ADC1) includes: a capacitor (C1); a charge and discharge control section (6) that puts, into the capacitor (C1), an electric charge corresponding to an input current of a first period and that causes an electric charge corresponding to an input current of a second period to be discharged from the capacitor (C1); and a digital conversion section (5) that converts an amount of electric charge of the capacitor (C1) into a digital signal.

Claims

1. An analog-digital conversion circuit comprising:

a first capacitor;

a digital conversion section that converts an amount of electric charge stored in the first capacitor into a digital signal; and

a charge and discharge control section that controls charge and discharge of the first capacitor,

the charge and discharge control section putting, into the first capacitor, an electric charge corresponding to an electric current inputted to the analog-digital conversion circuit during a first period,

the charge and discharge control section causing an electric charge corresponding to an electric current inputted to the analog-digital conversion circuit during a second period that follows the first period to be discharged from the first capacitor,

the charge and discharge control section performs more than once a charge and discharge cycle including (i) charging the first capacitor during the first period and (ii) discharging the first capacitor during the second period,

during an analog-digital conversion period that comes after the end of the charge and discharge control carried out by the charge and discharge control section, the digital conversion section converting an amount of electric charge stored in the first capacitor at the end of the charge and discharge control into a digital signal.

3. The analog-digital conversion circuit as set forth in claim 1, wherein:

the digital conversion section includes

(i) a second capacitor having a capacitance that is lower than the capacitance of the first capacitor and

(ii) a transfer section that transfers the electric charge stored in the first capacitor to the second capacitor during a charge-transfer period that comes after the end of the charge and discharge control carried out by the charge and discharge control section and that comes before the start of the analog-digital conversion period; and

the digital conversion section converts an amount of electric charge stored in the second capacitor at the end of the transfer of the electric charge by the transfer section into a digital signal.

4. The analog-digital conversion circuit as set forth in claim 1, wherein:

the charge and discharge control section includes

(i) an operational amplifier,

(ii) a first switch that changes between being turned on to and being turned off not to input, to an inverting input terminal of the operational amplifier, an electric current inputted to the analog-digital conversion circuit, and

(iii) a connection selection section that selects a state of connection between the operational amplifier and the first capacitor;

a reference voltage is applied to a non-inverting input terminal of the operational amplifier;

the connection selection section is capable of selecting between a first state of connection in which the inverting input terminal and an output terminal of the operational amplifier are connected to first and second terminals of the first capacitor, respectively, and a second state of connection in which the inverting input terminal and output terminal of the operational amplifier are connected to the second and first terminals of the first capacitor, respectively;

the charge and discharge control section controls the first switch to be on during the first and second periods and controls the first switch to be off during the analog-digital conversion period; and

the charge and discharge control section controls the connection selection section to select the first state of connection during the first period and to select the second state of connection during the second period.

5. The analog-digital conversion circuit as set forth in claim 4, wherein:

the digital conversion section includes

(i) a comparator that compares a voltage at the second terminal of the first capacitor with the reference voltage,

(ii) a discharge circuit that causes the first capacitor to discharge at a predetermined speed while the comparator determines that the voltage at the second terminal of the first capacitor is higher than the reference voltage, and

(iii) a counting circuit that counts the number of clocks during a period from a point in time where the comparator determined that the voltage at the second terminal of the first capacitor is higher than the reference voltage and a point in time where the comparator determines that the voltage at the second terminal of the first capacitor is lower than the reference voltage;

the charge and discharge control section further includes a second switch that changes between being turned on to connect and being turned off to disconnect the comparator to or from the second terminal of the first capacitor; and

the charge and discharge control section controls the second switch to be off during the first and second periods and controls the second switch to be on during the analog-digital conversion period.

6. The analog-digital conversion circuit as set forth in claim 3, wherein:

the charge and discharge control section includes

(i) an operational amplifier,

(ii) a first switch that changes between being turned on to and being turned off not to input, to an inverting input terminal of the operational amplifier, an electric current inputted to the analog-digital conversion circuit, and

(iii) a connection selection section that selects a state of connection between the operational amplifier and the first capacitor;

a reference voltage is applied to a non-inverting input terminal of the operational amplifier;

the connection selection section is capable of selecting between a first state of connection in which the inverting input terminal and an output terminal of the operational amplifier are connected to first and second terminals of the first capacitor, respectively, and a second state of connection in which the inverting input terminal and output terminal of the operational amplifier are connected to the second and first terminals of the first capacitor, respectively;

the charge and discharge control section controls the first switch to be on during the first and second periods and controls the first switch to be off during the analog-digital conversion period;

the charge and discharge control section controls the first and second capacitors to be disconnected from each other during the first period, the second period, and the analog-digital conversion period and controls the first and second capacitors to be connected to each other during the charge-transfer period; and

the charge and discharge control section controls the connection selection section to select the first state of connection during the first period and to select the second state of connection during the second period.

7. The analog-digital conversion circuit as set forth in claim 6, wherein the digital conversion section includes

(i) a comparator that compares a voltage at the second terminal of the second capacitor with the reference voltage,

(ii) a discharge circuit that causes the second capacitor to discharge at a predetermined speed while the comparator determines that the voltage at the second terminal of the second capacitor is higher than the reference voltage, and

(iii) a counting circuit that counts the number of clocks during a period from a point in time where the comparator determined that the voltage at the second terminal of the second capacitor is higher than the reference voltage and a point in time where the comparator determines that the voltage at the second terminal of the second capacitor is lower than the reference voltage.

8. The analog-digital conversion circuit as set forth in claim 5, wherein the charge and discharge control section connects both the inverting input terminal and output terminal of the operational amplifier to the first terminal of the first capacitor prior to the first period.

9. The analog-digital conversion circuit as set forth in claim 5, wherein the charge and discharge control section controls the second switch to be on prior to the first period so that an inverting input terminal and output terminal of the comparator get short-circuited.

10. The analog-digital conversion circuit as set forth in claim 7, wherein the charge and discharge control section connects both the inverting input terminal and output terminal of the operational amplifier to the first terminal of the first capacitor and the first terminal of the second capacitor prior to the first period.

11. The analog-digital conversion circuit as set forth in claim 7, wherein an inverting input terminal and output terminal of the comparator get short-circuited prior to the first period.

12. A sensor device comprising:

a light source that emits light toward an outside;

a light source drive section that drives the light source;

a photodiode that, in response to light from the outside, generates an electric current corresponding to the intensity of the light;

an analog-digital conversion circuit that converts the electric current into a digital signal; and

a signal processing section that processes the digital signal,

the analog-digital conversion circuit being an analog-digital conversion circuit as set forth in claim 1,

the light source drive section driving the light source during the first period and stops driving the light source during the second period.

13. The sensor device as set forth in claim 12, wherein the signal processing section compares the digital signal with a predetermined threshold value and determines, on the basis of a result of the comparison, whether or not an object is proximate to the sensor device at a predetermined distance or shorter.

14. The sensor device as set forth in claim 12, wherein the signal processing section compares the digital signal with a predetermined threshold value and determines a distance of an object to the sensor device on the basis of a result of the comparison.

15. The sensor device as set forth in claim 12, wherein:

the photodiode comprises a plurality of photodiodes;

the analog-digital conversion circuit comprises a plurality of analog-digital conversion circuits;

each of the analog-digital conversion circuits converts an electric current generated by a corresponding one of the photodiodes into a digital signal; and

the signal processing section determines a state of movement of an object with respect to the sensor device on the basis of a digital signal outputted from each of the photodiodes.

16. A cellular phone comprising a sensor device as set forth in claim 12.

17. A digital camera comprising a sensor device as set forth in claim 12.

2. (canceled)