Electrical transmission or interconnection systems – Nonlinear reactor systems – Parametrons
Patent
1983-06-13
1985-10-08
Miller, Stanley D.
Electrical transmission or interconnection systems
Nonlinear reactor systems
Parametrons
328145, 307490, G06G 712
Patent
active
045463212
DESCRIPTION:
BRIEF SUMMARY
This invention relates to non-linear amplifier systems, and more specifically to logarithmic amplifier systems for amplifying repetitive signals.
BACKGROUND OF THE INVENTION
Non-linear amplifiers such as logarithmic amplifiers find wide application especially in the communication field and in measurement instruments, such as, spectrum analyzers, sampling oscilloscopes, and time domain reflectometers for measuring the characteristics of electrical or optical signal transmission lines.
The input signal to be processed in the amplifier system of a measurement instrument such as a fiber optic time domain reflectometer may have a dynamic range which exceeds the dynamic range of a conventional linear amplifier. In order to permit use of such conventional linear amplifiers, the input signal is first processed by a circuit having a non-linear (e.g. logarithmic) transfer function, so as to compress the dynamic range of the input signal and thereby increase the apparent dynamic range of the overall amplifier system.
The dynamic range of the amplifier system may be increased further by using a linear preamplifier to amplify very weak signal components. A conventional preamplifier, however, cannot accept stronger signal levels, and thereby limits the dynamic range of the amplifier system in which it is used.
SUMMARY OF THE INVENTION
According to the present invention there is provided a non-linear amplifier system for a repetitive input signal, comprising a first amplifier stage for amplifying low level input signals in a liner manner and higher level input signals in a non-linear manner, whereby low level noise signals are amplified linearly; a sampling circuit for smoothing the output from said first amplifier stage and thereby reducing the amplitude of low level random noise signals; and a second amplifier stage for receiving the output from the sampling circuit and amplifying in non-linear manner signals corresponding to low level input signals of the first amplifier stage and amplifying in linear manner signals corresponding to higher level input signals of the first amplifier stage, whereby low level input signals can be amplified in non-linear manner without introducing substantial errors due to non-linear amplification of low level random noise signals.
In an embodiment of the invention, the amplifier system comprises first and second cascaded amplifier stages. The first amplifier stage amplifies low level input signals linearly and amplifies higher level input signals logarithmically, whereas the second amplifier stage amplifies low level signals logarithmetically and amplifies higher level signals linearly. The sampling circuit smooths the output from the first amplifier stage, eliminating random noise, since the noise level is below the level of signals that are amplified logarithmically by the first amplifier stage. The resulting non-linear amplifier system has a greater dynamic range than conventional amplifiers, and its useful dynamic range includes input signals below the system's input noise level.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:
FIG. 1 is a block diagram of an amplifier system embodying the present invention;
FIGS. 2 and 3 are graphs having values of output signal level plotted as ordinates on a linear scale and, as abscissae, values of input signal level plotted on a logarithmic scale;
FIG. 4 is a simplified schematic diagram of one portion of the first amplifier stage of the amplifier system;
FIG. 5 is a block diagram of the entire first amplifier system;
FIG . 6 is a combined block and schematic diagram of the amplifier system;
FIGS. 7A, 7B and 7C are schematic diagrams illustrating the first amplifier stage in greater detail than FIGS. 4 and 5; and
FIG. 8 is a schematic diagram of the second amplifier stage.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified block diagram of a non-linear amplif
REFERENCES:
patent: 3518578 (1970-06-01), Oppenheim
patent: 3875537 (1975-04-01), Dolby
patent: 3997845 (1976-12-01), Wegstedt
patent: 4287491 (1981-09-01), Scholz
patent: 4377792 (1983-03-01), Blackmer et al.
patent: 4418317 (1983-11-01), Bateman
Bateman Glenn
DuPuy, Jr. Richard E.
Davis B. P.
Miller Stanley D.
Smith-Hill John
Tektronix Inc.
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