Browse Prior Art Database

ENHANCED DYNAMIC RANGE DAC USING PWM TECHNIQUE

IP.com Disclosure Number: IPCOM000007437D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2002-Mar-26
Document File: 3 page(s) / 98K

Publishing Venue

Motorola

Related People

Michel Burri: AUTHOR [+2]

Abstract

The most common 8-bits MCU used to date, having a PWM unit, can be used to perform DAC. Unfortunately in most applications the 8-bits reso- lution is not suitable. IO-bits or more are ohen required to increase the dynamic range of the con- trolled system.

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0 M M-ROLA

Technical Developments

ENHANCED DYNAMIC RANGE DAC USING PWM TECHNIQUE

by Michel Burri and Pascal Renard

1 -INTRODUCTION

  The most common 8-bits MCU used to date, having a PWM unit, can be used to perform DAC. Unfortunately in most applications the 8-bits reso- lution is not suitable. IO-bits or more are ohen required to increase the dynamic range of the con- trolled system.

  This proposal satisfies the above requirements with advantage to offer a good flexibility in order to optimize different kind ofapplications.

gral (PI) features,

  To provide a better ripple voltage value the time constant and especially C2 can be increased, keep- ing the same settling time than an 8-bit classic PWM (Figure 1). The ripple voltage value can be reduced by a factor of 2cn+r) where n represents the number of bit added to achieve the R/2R ladder network
(i.e. figure 2, n = 3).

  Figure 3 shows another configuration where C3 produces a full integral term (I). The proportional term can be selected on different binary weights according to the required dynamic system.

2-DESCRIPTION

  The principle of the invention uses PWM fea- tures which modulates the LSB of an R/2R ladder network allowing us to create an enhanced dynamic range DAC.

A classic PWM (Figure 1) often has the follow- ing drawbacks for certain applications:

0 8-bits resolution (48db dynamic range)

too much ripple for acceptable time constant RCl

3-CONCLUSION

l

l too long settling time (Ts) to achieve accepta- ble ripple voltag...