Variable loop length compensated barrier circuit
AssigneeBell Telephone Laboratories, Incorporated
InventorsAlexander Feiner, Chao Kai Liu, Sigurd G. Waaben
Life of this patent
Estimating the term…
Abstract
A gain and frequency compensated barrier circuit is disclosed for use with a telephone transmission line having variable loop lengths. A DC component of the input signal is provided to the input side of the barrier circuit. Loop length losses, as well as barrier gain variations, are adjusted on the output side of the circuit by comparing a barrier DC voltage level with a DC reference level and adjusting the AC gain in accordance therewith. Frequency response, which is also a function of loop length, is corrected by using the DC input voltage to generate an effective loop length dependent capacitor for further controlling the output signal level. An optocoupled circuit is disclosed for use in one embodiment of the disclosure.
Claims16
An optocoupled device having an input terminal and an output terminal said terminals separated by a photocoupled barrier, the input side of said barrier containing phototransmitting means operable for providing phototransmission across said barrier in accordance with input AC and DC transmission signals, and the output side of said barrier containing photodetecting means operable under control of received phototransmission for providing an output transmission signal representative of said input transmission signal, said device including
- means on said input side of said barrier for generating a bias signal proportional to said input DC signal,
- means for applying said generated bias signal to said phototransmitting means so that one component of said phototransmission across said barrier is a function of said input DC transmission signal as well as a function of the physical characteristics of the light transfer across said barrier,
- means for comparing a reference DC voltage level to a DC voltage level generated by said photodetecting means as a result of received phototransmission, and
- means on said output side of said barrier for modifying the AC gain of said output transmission signal in accordance with said compared voltage levels.
A variable telephone loop length optocoupled isolation circuit having an input terminal connectable to said telephone loop and an output terminal connectable to a telephone station circuit said terminals separated by a photocoupled barrier, the input side of said barrier containing phototransmitting means operable for providing phototransmission across said barrier in accordance with input transmission signals, and the output side of said barrier containing photodetecting means operable under control of received phototransmission for providing an output transmission signal representative of said input transmission signal,
- means on said input side of said barrier for generating a DC voltage proportional to the length of said telephone loop,
- means for applying said generated DC voltage to said phototransmitting means so that the DC component of said phototransmission across said barrier is a function of said loop length as well as a function of the physical characteristics of the light transfer across said barrier,
- means for comparing a reference DC voltage level to a DC voltage level generated by said photodetecting means as a result of received phototransmission, and
- means for modifying the gain of said output transmission signal in accordance with said compared voltage levels.
A telephone communication system having a telephone central office transmission line connectable to a telephone station set via a switching network, said communication system including a circuit for isolating said transmission line from said switching network, said isolation circuit comprising
- an input terminal for connection to said transmission line and an output terminal for connecting to said switching network, said terminals separated by a photocoupled barrier, the input side of said barrier containing phototransmitting means operable for providing phototransmission across said barrier in accordance with input AC and DC transmission signals on said transmission line, and the output side of said barrier containing photodetecting means operable under control of received phototransmission for providing an output transmission signal representative of said input transmission signal,
- means on said input side of said barrier for generating a bias signal proportional to said input DC signal,
- means for applying said generated bias signal to said phototransmitting means so that one component of said phototransmission across said barrier is a function of said input DC transmission signal as well as a function of the physical characteristics of the light transfer across said barrier,
- means for comparing a reference DC voltage level to a DC voltage level generated by said photodetecting means as a result of received phototransmission, and
- means on said output side of said barrier for modifying the AC gain of said output transmission signal in accordance with said compared voltage levels.
An isolation device having an input terminal and an output terminal said terminals separated by an interface, the input side of said interface containing transmitting means operable for providing transmission across said interface in accordance with input AC and DC transmission signals, and the output side of said interface containing detecting means operable under control of received transmission for providing an output transmission signal representative of said input transmission signal, said device including
- means on said input side of said interface for generating a bias signal proportional to said input DC signal,
- means for applying said generated bias signal to said transmitting means so that one component of said transmission across said interface is a function of said input DC transmission signal as well as a function of the physical characteristics of said interface,
- means for comparing a reference DC voltage level to a DC voltage level generated by said detecting means as a result of transmission received across said interface, said
- means on said output side of said interface for modifying the AC gain of said output transmission signal in accordance with said compared voltage levels.
A variable telephone loop length isolation circuit having an input terminal connectable to said telephone loop and an output terminal connectable to a telephone station circuit said terminals separated by an isolation interface, the input side of said interface containing transmitting means operable for providing transmission across said interface in accordance with input transmission signals, and the output side of said interface containing detecting means operable under control of transmission received across said interface for providing an output transmission signal representative of said input transmission signal,
- means on said input side of said interface for generating a DC voltage proportional to the length of said telephone loop,
- means for applying said generated DC voltage to said transmitting means so that the DC component of said transmission across said interface is a function of said loop length as well as a function of the physical characteristics of said barrier,
- means for comparing a reference DC voltage level to a DC voltage level generated by said detecting means as a result of transmission received across said interface, and
- means for modifying the gain of said output transmission signal in accordance with said compared voltage levels.
Dependencies are inferred from the claim text.