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Digital-to-Analog Converter

IP.com Disclosure Number: IPCOM000101188D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Kobayashi, Y: AUTHOR [+2]

Abstract

This article describes a utility circuit used with a commercial 1-bit digital-to-analog converter (DAC). A 1-bit DAC module (such as a 6623 or 6471) receives 16-bit digital data and converts it into a Pulse Width Modulated (PWM) digital signal. The utility circuit, hereafter referred to as the DAU, effectively demodulates this PWM signal and makes an accurate analog signal. It has two functions: one is to demodulate the PWM signal and make a real analog signal, and the other is to control the volume of the analog signal. The DAU consists of the three portions shown in the figure.

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Digital-to-Analog Converter

       This article describes a utility circuit used with a
commercial 1-bit digital-to-analog converter (DAC). A 1-bit DAC
module (such as a 6623 or 6471) receives 16-bit digital data and
converts it into a Pulse Width Modulated (PWM) digital signal. The
utility circuit, hereafter referred to as the DAU, effectively
demodulates this PWM signal and makes an accurate analog signal. It
has two functions: one is to demodulate the PWM signal and make a
real analog signal, and the other is to control the volume of the
analog signal. The DAU consists of the three portions shown in the
figure.

      1. Current source (variable): The current source produces a
variable direct current corresponding to the signal strength. The
source actually consists of one DAC module, the DAC08 or its
equivalent. This current-sink-type DAC module produces a sink current
in response to 8-bit digital data. Three-digit bits control the
output current as follows:
 Control bit        000, 001, 010, 011, 100, 101, 110, 111
 Current strength     1,   2    4,   8,  16,  32,  64, 128
 This code conversion can be performed with a small amount of
combinational logic.  The voltage of the DAC module is carefully
regulated to reinforce Supply Voltage Rejection Ratio (SVRR)
characteristics.

      2. Current switch: The current switch produces a
source-and-sink current corresponding to the PWM signal of the 1-bit
DAC. An "H"-level signal produces a source cu...