Browse Prior Art Database

Sigdel Line Driver

IP.com Disclosure Number: IPCOM000037368D
Original Publication Date: 1989-Dec-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Ferry, M: AUTHOR [+2]

Abstract

Disclosed is a Limited Distance Modem (LDM) transmit front end circuit. The architecture of such a front end conventionaly includes a D/A converter, a filter for outband noise supression and a line driver. The advent of wide band Sigma-Delta conversion and CMOS logic now makes it possible to implement the three functions together. In the case of LDM multidrop lines, an impedance switching function can also be added with few extra components. The result is a drastic reduction of the front end number of parts and cost.

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Sigdel Line Driver

Disclosed is a Limited Distance Modem (LDM) transmit front end circuit. The architecture of such a front end conventionaly includes a D/A converter, a filter for outband noise supression and a line driver. The advent of wide band Sigma- Delta conversion and CMOS logic now makes it possible to implement the three functions together. In the case of LDM multidrop lines, an impedance switching function can also be added with few extra components. The result is a drastic reduction of the front end number of parts and cost.

Fig. 1 shows a possible block schematic for a sigdel line driver.

The sigdel converter is essentially made of a CMOS gate and an RC network. The low pass (LP) filter provides extra outband noise attenuation in order to prevent interference with other circuits. To avoid the modification of the line driver output impedance, the LP filter must be passive, makes use of the transformer usually found in such a circuit to ensure galvanic isolation leakage inductance associated with external capacitors perform the filtering function. Extra filtering can be implemented easily and at low cost by providing other digital sigdel signals. These signals are derivated from the original one by delaying it an integer number of sigdel clock unit intervals. One easily achieves transverse filtering by weighting and summing these signals. Fig. 2 shows an implementation with one delayed signal.

It can be interesting to digitally sum the original and del...