Line powered modem
First Claim
1. An inductance simulation circuit to be connected to a transmission line providing a line-holding direct current and carrying alternating data signals, the circuit being operative to exhibit a relatively low resistance to direct current flow between two points in the circuit whereby a d.c. power supply for energising data handling apparatus can be derived from said direct current flow and to exhibit a relatively high impedance for alternating signals occuring between those points, the circuit comprising resistance means connected between the points, and an amplifier circuit connected across the resistance means to provide a low resistance d.c. path in parallel with the resistance means and operative to amplify the alternating signals and to apply the amplified alternating signals across the resistance means in a phase such that the amplifier circuit simulates an inductance connected across the points.
1 Assignment
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Accused Products
Abstract
A modem or other data handling apparatus for connection to a transmission line includes an inductance simulation circuit for providing a low d.c. resistance to allow circulation of a line holding current, whilst presenting a high a.c. shunt impedance to the audio data tones on the line. The simulation circuit comprises two tranistors connected as a high gain amplifier across an input resistor in the modem/line coupling circuit amplifier via a capacitor and the amplifier applies tone signals across the input resistor to augment the tones thereacross. The conductive transistors also act as a low resistance connected across the input resistor for the passage of the line holding current. The simulation circuit acts, in effect, as an inductance, without the use of inductive components. The input resistor is effectively connected, in series with two zener diodes, across the line, and the series circuit receives the line voltage and produces therefrom positive and negative power supplies for energizing the entire modem. No further power supply is necessary.
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Citations
14 Claims
- 1. An inductance simulation circuit to be connected to a transmission line providing a line-holding direct current and carrying alternating data signals, the circuit being operative to exhibit a relatively low resistance to direct current flow between two points in the circuit whereby a d.c. power supply for energising data handling apparatus can be derived from said direct current flow and to exhibit a relatively high impedance for alternating signals occuring between those points, the circuit comprising resistance means connected between the points, and an amplifier circuit connected across the resistance means to provide a low resistance d.c. path in parallel with the resistance means and operative to amplify the alternating signals and to apply the amplified alternating signals across the resistance means in a phase such that the amplifier circuit simulates an inductance connected across the points.
Specification