Browse Prior Art Database

Public Switched Network Transmit Signal Level Adjustment

IP.com Disclosure Number: IPCOM000042643D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Jouffroy, JC: AUTHOR [+3]

Abstract

The attachment of a modem to the U.S. Public Switched Network is accomplished by the use of an FCC Registered Incorporated Protective Coupler (IPC) and a data jack which is provided by telephone companies. The data jack contains a program resistor whose value specifies the transmit signal level. This article describes a circuit that senses the program resistor value, automatically adjusts the transmit signal level in accordance with the sensed resistor value, and is insensitive to noise. As shown in Fig. 1, the output from the IPC comprises three pairs of wires. The first pair is the telephone pair (T(Tip), R(Ring)), the second pair (MI-MIC) is used to sense the exclusion key of the telephone associated with the IPC, and the third pair (PC-PR) is used to sense the program resistor RX located in the data jack housing.

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Public Switched Network Transmit Signal Level Adjustment

The attachment of a modem to the U.S. Public Switched Network is accomplished by the use of an FCC Registered Incorporated Protective Coupler (IPC) and a data jack which is provided by telephone companies. The data jack contains a program resistor whose value specifies the transmit signal level. This article describes a circuit that senses the program resistor value, automatically adjusts the transmit signal level in accordance with the sensed resistor value, and is insensitive to noise. As shown in Fig. 1, the output from the IPC comprises three pairs of wires. The first pair is the telephone pair (T(Tip), R(Ring)), the second pair (MI-MIC) is used to sense the exclusion key of the telephone associated with the IPC, and the third pair (PC-PR) is used to sense the program resistor RX located in the data jack housing. The proposed circuit, illustrated in Fig. 2 and which is located within the IPC, senses the value of the program resistor RX which is provided by the telephone company at installation time and which specifies the appropriate transmit signal level for the attached local loop and adjusts the transmit level in accordance with the sensed resistor value. The output from the modem is coupled, in parallel, to the input of two operational amplifiers (OAs) 10 and 12 having +1 and -1 gains, respectively. The outputs from OAs 10 and 12 are respectively applied to the two inputs of operational amplifier 14...