Circuit and method for active termination of a transmission line
First Claim
1. A line driver with back-matching impedance emulation having a transmission line termination control loop, comprising:
- a power amplifier having a power amplifier transmit gain configured with a first input for receiving a transmit signal, a second input for receiving an amplified feedback signal, and an output configured to provide an amplified transmit signal to the transmission line;
a current sensing means electrically coupled to the power amplifier output and configured to generate a feedback input signal;
a feedback amplifier having a negative transresistance forward transfer function configured to receive the feedback input signal and provide an amplified feedback signal to the second input of the power amplifier;
a first amplifier configured to receive the amplified feedback signal and apply a first amplifier transmit gain equivalent to the inverse of the power amplifier transmit gain to provide a first amplifier output signal; and
a second amplifier configured to receive a first input comprising at least one signal from the transmission line and a second input comprising the first amplifier output signal, the second amplifier configured to mathematically combine the input signals to generate a scaled version of the transmit signal.
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Accused Products
Abstract
An improved line driver and method for increasing the power efficiency, signal accuracy, and stability of a transmit signal on a transmission line are disclosed. The improved line driver uses a negative feedback control loop, thereby enhancing operational stability and suppressing both amplifier imperfections and discrete component manufacturing variances. Furthermore, when the improved line driver output stage is integrated with a hybrid, the composite circuit provides a power efficient full duplex solution for line driver applications. In a preferred embodiment, the improved line driver may comprise an active line termination control loop with current sense feedback, a first amplifier, and a second amplifier. The present invention can also be viewed as providing a method for increasing the stability, power efficiency, and accuracy of a line driver in a duplex transmission system. In its broadest terms, the method can be described as: applying a transmit signal to an input stage of a line driver; amplifying the transmit signal; using an active termination feedback control loop to generate a feedback signal; amplifying the feedback signal; combining the feedback signal with a duplex signal on a transmission line to generate a scaled transmit signal; and combining the scaled transmit signal with the duplex signal to recover a remotely generated receive signal from the transmission line.
53 Citations
26 Claims
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1. A line driver with back-matching impedance emulation having a transmission line termination control loop, comprising:
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a power amplifier having a power amplifier transmit gain configured with a first input for receiving a transmit signal, a second input for receiving an amplified feedback signal, and an output configured to provide an amplified transmit signal to the transmission line;
a current sensing means electrically coupled to the power amplifier output and configured to generate a feedback input signal;
a feedback amplifier having a negative transresistance forward transfer function configured to receive the feedback input signal and provide an amplified feedback signal to the second input of the power amplifier;
a first amplifier configured to receive the amplified feedback signal and apply a first amplifier transmit gain equivalent to the inverse of the power amplifier transmit gain to provide a first amplifier output signal; and
a second amplifier configured to receive a first input comprising at least one signal from the transmission line and a second input comprising the first amplifier output signal, the second amplifier configured to mathematically combine the input signals to generate a scaled version of the transmit signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An improved line driver having an output load current, comprising:
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means for amplifying a transmit signal; and
means for emulating a back-matching resistance using a negative feedback circuit configuration wherein the means for emulating a back-matching resistance is accomplished by amplifying a feedback signal responsive to the output load current such that the emulated back-matching resistance appears to have a resistance value equivalent to the product of the transmit signal amplification gain and the feedback signal amplification gain. - View Dependent Claims (15)
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16. A signal transmission unit having a transmit signal amplification gain, comprising:
- a line driver in cooperation with a negative feedback transmission line termination control loop having a feedback signal amplification gain that emulates a back-matching resistor having a resistance value equivalent to the product of the transmit signal amplification gain and the feedback signal amplification gain.
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17. A communications system having a transmit signal amplification gain, comprising:
- a transmission unit having a line driver, the line driver having a negative feedback transmission line termination control loop having a feedback signal amplification gain that emulates a back-matching resistor having a resistance value equivalent to the product of the transmit signal amplification gain and the feedback signal amplification gain.
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18. A method for increasing the power efficiency, signal accuracy, and stability of a transmit signal on a transmission line, comprising:
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applying a transmit signal to an input of a line driver;
amplifying the transmit signal;
applying the amplified transmit signal to a transmission line load to generate a load current;
sensing the load current;
applying the sensed load current in a negative feedback transmission line termination control loop having a feedback amplifier to generate an amplified feedback signal responsive to the load current such that an output impedance emulates a back-matching resistor wherein the transmit gain of the feedback amplifier is controllably adjusted in response to scaling errors associated with the sensed load current. - View Dependent Claims (19, 20, 21)
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22. A method for recovering a remotely generated signal from a transmission line in a duplex communication system, comprising:
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applying a transmit signal to an input stage of a line driver;
amplifying the transmit signal with a line driver amplifier;
using an active termination feedback control loop in cooperation with the line driver amplifier to generate a feedback signal responsive to a load current;
applying the amplified transmit signal on the transmission line;
amplifying the feedback signal to generate a line driver output impedance that emulates a back-matching resistor;
further amplifying the feedback signal with an inverted transmit gain substantially equivalent in magnitude with the gain of the line driver amplifier;
combining the further amplified feedback signal with a duplex signal on the transmission line to generate a scaled transmit signal; and
combining the scaled transmit signal with the duplex signal to recover a remotely generated receive signal from the transmission line. - View Dependent Claims (23, 24, 25, 26)
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Specification