Digital-to-analog converter with greater output resistance

• US 8,643,521 B1
• Filed: 11/28/2012
• Issued: 02/04/2014
• Est. Priority Date: 11/28/2012
• Status: Active Grant

• Current Assignee: United Microelectronics Corporation
• Original Assignee: United Microelectronics Corporation
• Inventors: Cheng, Hsueh-Chen, Hsu, Wen-Hong, Chen, Po-Hua, Liow, Yu-Yee
• Primary Examiner(s): Nguyen, Khai M
• Application Number:
  US13/688,158
• Time in Patent Office: 433 Days
• Field of Search: 341/136, 341/144, 341/154
• US Class Current: 341/136
• CPC Class Codes: H03M 1/0818 of clock feed-through
• CPC Class Codes: H03M 1/742 using current sources as quantisation value generators

Abstract

A DAC has at least one bit current-steering circuit. In the DAC, the current-steering circuit has a current source circuit, a switch, a feedback circuit, and an amplifier circuit. The current source circuit is disposed for outputting a bias current to the switch and coupled to the amplifier circuit. The switch has a first input/output terminal coupled to output an analog signal, a control terminal coupled to the feedback circuit, and a second input/output terminal for receiving the bias current, so that the first switch determines whether the first and the second input/output terminals are conducted according to a status of the control terminal.

Claims

1. A digital-to-analog converter, having at least one bit current-steering circuit, and the current-steering circuit comprising:

a current source circuit for outputting a bias current;

a first switch having a first input/output terminal coupled to a first output terminal of the current-steering circuit, a control terminal, and a second input/output terminal coupled to the current source circuit to receive the bias current, wherein the first switch determines whether the first and the second input/output terminals are conducted by one another according to a status of the control terminal;

a first feedback circuit coupled to the first switch, including;

a first transistor having a first source/drain terminal coupled to the control terminal of the first switch, a second source/drain terminal, and a gate terminal; and

a first resistance element having a first terminal coupled to the gate terminal of the first transistor, and a second terminal coupled to the first input/output terminal of the first switch; and

a first amplifier circuit having an input terminal coupled to the second input/output terminal of the first switch, an output terminal coupled to the second source/drain terminal of the first transistor, and a voltage terminal coupled to a voltage source.

2. The digital-to-analog converter according to claim 1, wherein the current source circuit comprises:

a second transistor having a first source/drain terminal coupled to the first input/output terminal of the first switch to output the bias current, a gate terminal coupled to a first bias voltage, and a second source/drain terminal; and

a third transistor having a first source/drain terminal coupled to the second source/drain terminal of the second transistor, a gate terminal coupled to a second bias voltage, and a second source/drain terminal coupled to the voltage source.

3. The digital-to-analog converter according to claim 1, wherein the first switch has a fourth transistor having a first and a second source/drain terminals as the first and the second input/output terminals, and a gate terminal as the control terminal.

4. The digital-to-analog converter according to claim 1, wherein the first amplifier circuit has an OP amplifier.

5. The digital-to-analog converter according to claim 1, wherein the first amplifier circuit is a common source amplifier.

6. The digital-to-analog converter according to claim 1, wherein the current-steering circuit further comprises:

a fifth transistor having a first source/drain terminal coupled to a common voltage, a gate terminal coupled to the control terminal of the first switch through a first capacitor and receiving a switch signal, and a second source/drain terminal; and

a sixth transistor having a first source/drain terminal coupled to the second source/drain terminal of the fifth transistor, a gate terminal coupled to a control signal, and a second source/drain terminal coupled to the control terminal of the first switch.

7. The digital-to-analog converter according to claim 1, wherein the current-steering circuit further comprises:

a second switch having a first input/output terminal coupled to a second output terminal of the current-steering circuit, a control terminal, and a second input/output terminal coupled to the current source circuit to receive the bias current, wherein the second switch determines whether the first and the second input/output terminals of the second switch are conducted according to a status of the control terminal;

a second feedback circuit coupled to the second switch, including;

a seventh transistor having a first source/drain terminal coupled to the control terminal of the second switch, a second source/drain terminal, and a gate terminal; and

a second resistance element having a first terminal coupled to the gate terminal of the seventh transistor, and a second terminal coupled to the first input/output terminal of the second switch; and

a second amplifier circuit having an input terminal coupled to the second input/output terminal of the second switch, an output terminal coupled to the second source/drain terminal of the seventh transistor, and a voltage terminal coupled to the voltage source.

8. The digital-to-analog converter according to claim 7, wherein the current-steering circuit further comprises:

a eighth transistor having a first source/drain terminal coupled to the common voltage, a gate terminal coupled to the control terminal of the second switch through a second capacitor and receiving an inverted switch signal, and a second source/drain terminal; and

a ninth transistor having a first source/drain terminal coupled to the second source/drain terminal of the eighth transistor, a gate terminal coupled to a control signal, and a second source/drain terminal coupled to the control terminal of the second switch.

9. The digital-to-analog converter according to claim 7, wherein the second amplifier circuit has an OP amplifier.

10. The digital-to-analog converter according to claim 7, wherein the second amplifier circuit is a common source amplifier.