ANALOG-TO-DIGITAL CONVERTER

• US 20090040083A1
• Filed: 06/25/2008
• Published: 02/12/2009
• Est. Priority Date: 08/07/2007
• Status: Active Grant

• Current Assignee: Himax Technologies Ltd. (Himax Technologies Incorporated), Jiun-Lang Huang
• Original Assignee: Himax Technologies Ltd. (Himax Technologies Incorporated), Jiun-Lang Huang
• Inventors: LEE, CHUAN-CHE, HUANG, JIUN-LANG, HUANG, JUI-JER
• Granted Patent: US 7,616,147 B2
• Time in Patent Office: Days
• US Class Current: 341/120
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: H03M 1/109 for dc performance, i.e. static testing H03M1/1085 takes precedence
• CPC Class Codes: H03M 1/56 Input signal compared with linear ramp
• CPC Class Codes: Y10S 345/904 Display with fail/safe testing feature

Abstract

An analog-to-digital converter (ADC) is presented. The ADC includes an error amplifier, a ramp generator, and a counting circuit. The error amplifier is used for receiving an output voltage and a reference voltage, and amplifying a difference between the output voltage and the reference voltage, so as to obtain a first voltage and a second voltage. The ramp generator is used for generating a ramp voltage which is increased along with time. The counting circuit is used for starting counting a digital value when the ramp voltage is larger than or equal to the first voltage, and stopping counting and outputting the digital value when the ramp voltage is larger than or equal to the second voltage.

Claims

1. An analog-to-digital converter (ADC), comprising:

an error amplifier, used for receiving an output voltage and a reference voltage, and amplifying a difference between the output voltage and the reference voltage, so as to obtain a first voltage and a second voltage;

a ramp generator, used for generating a ramp voltage which is increased along with time; and

a counting circuit, used for starting counting a digital value when the ramp voltage is larger than or equal to the first voltage, and stopping counting and outputting the digital value when the ramp voltage is larger than or equal to the second voltage.

2. The ADC according to claim 1, further comprising:

a correcting unit, having a correction mode and a test mode, for receiving and providing a first correction voltage and a second correction voltage to the error amplifier when the correction unit is in the correction mode, and then the error amplifier amplifies a difference between the first correction voltage and the second correction voltage, so as to obtain the first voltage and the second voltage,

wherein the correction unit determines whether to compensate the ADC based on the digital value generated by the ADC according to the first correction voltage and the second correction voltage, so as to eliminate errors of the ADC itself.

3. The ADC according to claim 2, wherein the correction unit receives and provides the output voltage and the reference voltage to the error amplifier when the correction unit is in the test mode, and then the error amplifier amplifies the difference between the output voltage and the reference voltage, so as to obtain the first voltage and the second voltage.

4. The ADC according to claim 3, wherein the correction unit is determined to be in the correction mode or in the test mode based on a control signal generated by an external digital testing machine.

5. The ADC according to claim 1, wherein the counting circuit comprises:

a first comparator, having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the first comparator receives the ramp voltage, the second input terminal of the first comparator receives the first voltage, and the output terminal of the first comparator outputs a first enabling signal when the ramp voltage is larger than or equal to the first voltage;

a second comparator, having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the second comparator receives the ramp voltage, the second input terminal of the second comparator receives the second voltage, and the output terminal of the second comparator outputs a second enabling signal when the ramp voltage is larger than or equal to the second voltage; and

a counter, for starting counting the digital value when the first enabling signal is enabled, and stopping counting and outputting the digital value when the second enabling signal is enabled.

6. The ADC according to claim 1, wherein the counting circuit comprises:

a first comparator, having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the first comparator receives the ramp voltage, the second input terminal of the first comparator receives the first voltage, and the output terminal of the first comparator outputs a first enabling signal when the ramp voltage is larger than or equal to the first voltage;

a second comparator, having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the second comparator receives the ramp voltage, the second input terminal of the second comparator receives the second voltage, and the output terminal of the second comparator outputs a second enabling signal when the ramp voltage is larger than or equal to the second voltage;

a logic gate, for receiving the first enabling signal and the second enabling signal, and outputting a logic enabling signal accordingly; and

a counter, for starting counting the digital value when the logic enabling signal is enabled, and stopping counting and outputting the digital value when the logic enabling signal is disabled.

7. The ADC according to claim 1, wherein the error amplifier comprises:

a fully-differential amplifier, having a positive input terminal, a negative input terminal, a positive output terminal and a negative output terminal, wherein the positive input terminal of the fully-differential amplifier receives the output voltage, the negative input terminal of the fully-differential amplifier receives the reference voltage, the positive output terminal of the fully-differential amplifier outputs the first voltage, and the negative output terminal of the fully-differential amplifier outputs the second voltage.

8. The ADC according to claim 7, wherein the error amplifier further comprises:

a first capacitor, having a first terminal and a second terminal, wherein the first terminal of the first capacitor receives the output voltage, and the second terminal of the first capacitor is coupled to the positive input terminal of the fully-differential amplifier;

a second capacitor, having a first terminal and a second terminal, wherein the first terminal of the second capacitor receives the reference voltage, and the second terminal of the second capacitor is coupled to the negative input terminal of the fully-differential amplifier;

a third capacitor, coupled between the positive input terminal and the negative output terminal of the fully-differential amplifier; and

a fourth capacitor, coupled between the negative input terminal and positive output terminal of the fully-differential amplifier.