Reference ladder having improved feedback stability

• US 6,885,236 B2
• Filed: 10/30/2002
• Issued: 04/26/2005
• Est. Priority Date: 06/14/2002
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Vorenkamp, Pieter
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): ENGLUND, TERRY LEE
• Application Number:
  US10/283,088
• Publication Number:
  US 20030231051A1
• Time in Patent Office: 909 Days
• Field of Search: 327/104, 327/538, 327/540, 341/154, 341/155
• US Class Current: 327/540
• CPC Class Codes: H03M 1/0602 of deviations from the desired transfer characteristic H03M1/0617 takes precedence
• CPC Class Codes: H03M 1/365 the voltage divider being a single resistor string

Abstract

A reference ladder is configured to have improved feedback stability. The reference ladder includes a resistor ladder having a plurality of taps that produce a plurality of reference voltages. The resistor ladder is driven by a first current source at a first tap of the plurality of taps and by a second current source at a second tap of the plurality of taps. A first feedback network senses a voltage at the first tap and controls the first current source based on the first sensed voltage. A second feedback network senses a voltage at the second tap and controls the second current source based on the second sensed voltage. The first and second taps each operate as both a force tap and a sense tap of the resistor ladder. Differential input stages that are connected to the plurality of taps are at least partially isolated from the feedback networks by converging the force and sense taps, thereby improving the stability of the feedback networks. An alternate embodiment includes first and second resistor ladders that are configured to generate substantially identical voltages across their respective taps. First and second feedback networks sense voltages on the first resistor ladder and control current sources that drive both the first resistor ladder and the second resistor ladder. Differential input stages that are connected to the taps of the second resistor ladder and are at least partially isolated from the feedback networks that are connected to the first resistor ladder, thereby improving stability of the feedback networks.

Claims

1. A reference ladder, comprising:

a first resistor ladder having a first plurality of taps and driven by a first variable current source at a first force tap, one of said plurality of taps being a sense tap;

a second resistor ladder having a second plurality of taps and driven by a second variable current source at a second force tap to provide a plurality of output voltages; and

a feedback network sensing a voltage at said sense tap of said first resistor ladder, and controlling said first variable current source and said second variable current source based on said voltage that is sensed at said sense tap.

2. The reference ladder of claim 1, wherein said sense tap is determined based on a full scale range voltage.

3. The reference ladder of claim 1, wherein said plurality of taps of said second resistor ladder are connected to a plurality of differential input stages that receive said plurality of output voltages.

4. The reference ladder of claim 3, wherein said plurality of differential input stages are at least partially isolated from said feedback network by said second resistor ladder.

5. The reference ladder of claim 3, wherein said first resistor ladder is driven by a third variable current source at a third force tap, and said second resistor ladder is driven by a fourth variable current source at a fourth tap, and further comprising a second feedback network sensing a voltage at a second sense tap of said first resistor ladder, and controlling said third variable current source and said fourth variable current source based on said voltage that is sensed at said second sense tap.