Browse Prior Art Database

TRANSVERSE TAX PULSES REGULATOR

IP.com Disclosure Number: IPCOM000005692D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-26
Document File: 2 page(s) / 99K

Publishing Venue

Motorola

Related People

Patrick Clement: AUTHOR

Abstract

Tax pulses sent in differential mode onto a telephone subscriber line are specified as having a given voltage magnitude. The MALC system which has to produce such tax pulses feeds the line with current. Thus a closed loop is required to regulate the magnitude of the tax pulses at the 2.wire port. This regulator also allows the pulses to be cadenced and to be smoothed by introducing controlled rise and fall times. FIG. 1 summarizes what is achieved by the tax pulse regulator.

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MOTOROLA Technical Developments Volume 7 October 1987

TRANSVERSE TAX PULSES REGULATOR

by Patrick Clement

   Tax pulses sent in differential mode onto a telephone subscriber line are specified as having a given voltage magnitude. The MALC system which has to produce such tax pulses feeds the line with current. Thus a closed loop is required to regulate the magnitude of the tax pulses at the 2.wire port. This regulator also allows the pulses to be cadenced and to be smoothed by introducing controlled rise and fall times. FIG. 1 summarizes what is achieved by the tax pulse regulator.

   FIG. 2 shows the block diagram of the regulator and FIG. 3 illustrates the generation of a pulse. A reference sine wave at 12kHz or 16kHz has to be forced on pin VRTAX. This signal is handled by an amplifier whose gain is programmable by means of an R-2R network. The amplified signal is then converted into a current buffered in the HV-MALC and sent onto the line. The impedance of the load at the 2-wire port at tax signal frequencies may be inductive or capacitive. Thus there will be a phase rotation between the line voltage and the signal on VRTAX pin. Moreoverthe line voltage at tax signal frequencies may not be regulated with a simple AGC system. For this reason in the proposed solution the output of the high-pass filter delivers an image of the line voltage component at 12 or 16kHz. Peak values of this signal and of VRTAX reference signal are compared into the peak comparator. The result is used to increment or decrement an a-bit up/down counter which controls the programmable gain of the output amplifier. Thus the loop is closed. Note that the magnitude of the signal on VRTAX has to be an image of the signal to be sent at the 2-wire port. This regulator features a zero ouput im- pedance at tax signal frequencies without altering signals in the voice band.

   Some other features are also provided. By means of the threshold comparator, the tax loop sequencer and the up-count...