Digital-to-analog converter with high linearity

• US 5,270,716 A
• Filed: 11/18/1991
• Issued: 12/14/1993
• Est. Priority Date: 05/18/1989
• Status: Expired due to Term

• Current Assignee: Deutsche Thomson-Brandt Gmbh (Vantiva SA)
• Original Assignee: Deutsche Thomson-Brandt Gmbh (Vantiva SA)
• Inventors: Gleim, Gunter
• Primary Examiner(s): Williams, Howard L.
• Application Number:
  US07/792,873
• Time in Patent Office: 757 Days
• Field of Search: 341/118, 341/144, 341/145
• US Class Current: 341/145
• CPC Class Codes: H03M 1/069 by range overlap between successive stages or steps
• CPC Class Codes: H03M 1/68 with conversions of different sensitivity, i.e. one conversion relating to the more significant digital bits and another conversion to the less significant bits

Abstract

A high linearity digital-to-analog converter (D/A) provides a linear output voltage using two D/A'"'"'s. One D/A provides a number of coarse steps and another D/A increments the output voltage within the coarse steps using fine steps. Discontinuities in the output voltage caused by the changing from one coarse step to another are avoided by using reference voltages which ensure that the initial voltage available at the start of a coarse step is lower than the final voltage available at the end of the preceeding step.

Claims

1. Apparatus for generating offset values for linearizing nonlinearities produced by the upper N more significant bits (MSB'"'"'s) of an M-bit digital-to-analog converter, M and N being integers with M>

N, said digital-to-analog converter including an N-bit upper MSB digital-to-analog converter and an (M-N)-bit lower LSB digital-to-analog converter, each having a respective analog output terminal coupled to an analog signal summing means for providing said digital-to-analog converter output values, said apparatus comprises;

comparing means for comparing analog output values provided by said analog signal summing means with threshold values;

threshold value generating means including a source of constant potential having a value substantially equal to the analog difference represented by one unit change of said MSB'"'"'s plus a predetermined value (b); and

means for serially coupling said source of constant potential between an input of said comparing means and the analog output terminal of said upper MSB digital-to-analog converter;

control means arranged for

1) providing respective MSB values, and for ones of such MSB values, incrementing said LSB values to provide consecutive values substantially over the range said M-N LSB'"'"'s may represent; and

2) for storing, responsive to said comparing means, respective LSB values occurring when output signal provided by said digital-to-analog converter crosses a respective threshold value; and

3) for subtracting pairs of said stored LSB values corresponding to successive values exhibited by said MSB'"'"'s to provide differences corresponding to said offset values.