Browse Prior Art Database

Digital-To-Analog Converter Multiplexing

IP.com Disclosure Number: IPCOM000046420D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Belloc, J: AUTHOR [+2]

Abstract

In a modem transmission system, the line signal is in analog form while most of the modem signal processing is performed digitally. In other words, the received analog input from the transmission line has to be converted using an analog-to-digital converter, while the signal to be transmitted over the same line has to go through a digital-to-analog converter (DAC).

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Digital-To-Analog Converter Multiplexing

In a modem transmission system, the line signal is in analog form while most of the modem signal processing is performed digitally. In other words, the received analog input from the transmission line has to be converted using an analog-to-digital converter, while the signal to be transmitted over the same line has to go through a digital-to-analog converter (DAC).

The analog-to-digital conversion is conventionally performed through successive approximation operations involving the use of comparator circuits and a DAC. Therefore, whenever both transmit and receive modem operations are to be performed using a single microprocessor, one may wish to share the same DAC for both receive and transmit modem sections. One may even wish to multiplex the DAC between several users. Means are provided here for performing these sharing and multiplexing DAC functions.

Assume the transmit register (TMXREG) has been loaded with a sample value. A transmit PLO (phase-locked oscillator) provides timing signals designated MUXTMX and data XSH respectively used for controlling a multiplexer (MUX) and a transmitter sample-and-hold (TMXSH) register. When the MUXTMX is on, the multiplexer is switched so that the TMXREG output is linked to the DAC input. The PLO output also inhibits the output comparator COMP of the analog-to-digital converter. During the XSH signal, the TMXSH register is activated and converts the DAC digital output into analog voltage. At the falling edge of MUXTMX, a transmitter interrupt (TMXINT) latch is set. The TMXINT pulse warns the signal proce...