JPS6270930A - Signal processing method and device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention converts weak electrical signals, such as weak optical signals, into optical signals.
The present invention relates to a method and apparatus for amplifying an electrically converted weak signal using a high-gain amplifier, and processing it by AD converting it. In general, an AC amplifier is used to amplify weak signals,
It compensates so that the O level of the signal waveform (O level) is always kept constant despite changes in the amplified signal waveform and amplitude, improving the linearity of the amplifier and improving dynamic performance.
The present invention relates to a method and apparatus for extremely minimizing range fluctuations, sampling amplified signals at high speed, and performing AD conversion and processing. Specifically, optical time domain
An improved method and apparatus suitable for signal amplification and processing of a reflectometer (OTDR) is provided.

[Prior art] Recently, cutting-edge technologies such as optical communication technology have made remarkable progress supported by high-speed semiconductor technology, but in these fields, there is a need for broadband, low-noise, and high-gain amplifiers. Increasingly high performance has become an important issue.

The optical signal is amplified after optical-to-electrical conversion, but since the signal is weak, a high interest rate of 1q is required for its amplification.
To this end, it is advantageous not only in terms of performance but also in terms of cost, to use an AC amplifier with a sufficiently low low cutoff frequency, rather than connecting multiple stages of DC amplifiers that have the inevitable drift problem.

In optical communications and the like, since there is no need to use a DC amplifier, AC amplifiers are increasingly being used because they do not have drift problems, operate from a single power supply, are compact, and have low power consumption.

However, in measuring optical signals, for example, measuring fiber characteristics or detecting break points, a device (hereinafter referred to as In the case of 0TDR), it is necessary to accurately know the O level of the weak signal transmitted by the reflected wave, and it is necessary to use a DC amplifier.

However, in reality, DC amplifiers are not necessarily suitable for amplifying minute signals due to problems with drift, difficulty in multi-stage connections, and the need for multiple power supplies.

In particular, in the case of 0TDR, the amplitude of the reflected wave from near the measurement end is extremely large, and the amplitude of the reflected wave from far away is minute. A wide range of amplifiers was the most important issue.

0TDR amplifies the backscattered light due to fiber Rayleigh scattering and the reflected wave due to Fresnel reflection at discontinuous parts such as fiber connections and breaks, in order to widen the dynamic range and observe the attenuation characteristics of the fiber. For convenience, a logarithmic amplifier is used.

However, for 0TDR, for the reasons mentioned above, an amplifier with a wide band, high gain, and wide dynamic range is required. When the waveform is a pulse waveform, for example, the operating level of the amplifier fluctuates due to fluctuations in its duty ratio, etc., which has the drawback of seriously affecting the dynamic range and accuracy.

In particular, in the case of a logarithmic amplifier, fluctuations in the operating level due to its logarithmic characteristics cause a significant deterioration in measurement accuracy, so sufficient performance could not be achieved without compensation to stabilize the operating level. It is.

This problem will be specifically explained below using FIG. 5 (a> to d).

In FIG. 5, (a) shows an example of a conventional broadband light receiving circuit. 11 is a preamplifier which is a DC amplifier, and 42 is an AC amplifier, such as a logarithmic amplifier IC (integrated circuit).
42a, 42b and coupling capacitor 44.45
A signal is applied from the output terminal 15 of the DC amplifier 11 via the coupling capacitor 43. 14 is APD (
A light receiving element such as an avalanche (1~diode) V,
is its bias power supply, and the output of the light receiving element 14 passes through the input terminal 13 of the preamplifier 11, is amplified by the preamplifier 11 and the AC amplifier 42, and the output can be obtained at the output terminal 49 of the AC amplifier 42. can.

Here, the number of stages of the logarithmic amplifier ICs 42a, 42b, etc. may be increased as necessary, and a high-interest 1q IC is also possible.

When the light-receiving element 14 receives backscattered light in the 0TDR described above, it is amplified by the preamplifier 11, and a waveform as shown in FIG. 5(C) is obtained at its output terminal 15. In (C), the dotted line is the level (
O level).

However, when this signal is passed through a circuit (b) that equivalently shows the coupling capacitor C between each stage of the AC amplifier and the input impedance R, it becomes as shown in (d), and the waveform in (C) is This results in a shift of S. The amount S of this shift varies depending on the amount of backscattered light, the magnitude of Fresnel reflected light, the repetition of optical pulses, that is, changes in the duty cycle, etc. If the O level fluctuates in this way, accurate amplification cannot be expected if the gain j1 changes depending on the signal level, such as in a logarithmic amplifier. In particular, as logarithmic amplifiers are connected in multiple stages, the amplification error increases synergistically, and the usable dynamic range becomes significantly narrower.

Furthermore, even when a general AC amplifier is used, fluctuations in the O level cause precision deterioration in applications such as analog-to-digital converters that require precision.

When a signal is applied to an AC amplifier, the operating level of the amplifier fluctuates depending on the waveform, resulting in an error in the amplification degree and a fluctuation in the dynamic range.

In order to solve this problem, the applicant filed a patent application in 1983.
~149146. 59-149147 and 59-
149148 was filed.

One reason for fluctuations in the O level when a signal waveform is applied to an AC amplifier is the positive amplitude component of the signal waveform (
This is because the area of the waveform in the positive direction) and the one-line width component in the negative direction (area of the waveform in the negative direction) are not equal.If these width components are not equal, for example, as shown in Figure 5(C) In the case of a waveform as shown in , if this waveform is directly applied to the AC amplifier 42, the operating level of the AC amplifier 42 will fluctuate.

Therefore, for example, in the above-mentioned patent application No. 9-149147, when there is an output from the preamplifier 11 shown in FIG. 6 (a), an inverted signal (FIG. 6 (b)) is created, and (a)
Signals are taken out alternately from both waveforms shown in c15 and (b), and a negative amplitude component equal to the positive amplitude component is synthesized as shown in Fig. 6 (C). A signal (C) is applied to an AC amplifier 42 to obtain an amplified signal.

A portion of the amplified signal corresponding to the signal shown in (a),
That is, the positive amplitude component of the composite signal shown in (C) is sampled (), AD converted, and averaged to remove noise.

[Problems to be Solved by the Invention] When measuring a long-distance fiber with 0TDR, the signal becomes minute and is therefore buried in noise. Therefore, this noise is removed by sampling the same point of a repeating signal waveform many times, performing AD conversion, and performing averaging processing.

However, even if there is an output from the preamplifier 11 shown in FIG.
Since the synthesized wave shown in Figure (C) was amplified, only the positive amplitude component of this wave was sampled, AD converted, and averaged, half of the waveform shown in Figure 6 (a) There is a problem in that only the waveform is used for measurement, and measurement requires twice as much time.

[Means for Solving the Problems] The present invention has been made to solve these problems.

The output of the preamplifier (Fig. 6 (a)) is obtained with a signal of opposite polarity (Fig. 6 (b)), and both signals are synthesized (Fig. 6 (C)).
), this was sampled and AD converted, and the polarity of the negative amplitude component (the part corresponding to FIG. 6(b)) was reversed and averaged.

[Effect] As a result, the amplitude component in the negative direction of the composite signal (FIG. 6(C)) also becomes the amplitude component in the positive direction (FIG. 6(a)).
Since the averaging process is performed in the same way as above, it is now possible to perform the averaging process in half the time compared to the conventional technology.

It is possible to sufficiently amplify minute signals with an AC amplifier without fluctuations in the O level, and for negative amplitude components,
Since the polarity is reversed and used after AD conversion, it is possible to perform averaging processing at high speed.

[Embodiment] This will be explained with reference to FIG. 1 showing the configuration of an embodiment of the present invention, and FIG. 2 showing waveforms of various parts for explaining its operation. Here, components corresponding to those in FIG. 5 are given the same reference numerals.

In FIG. 1, 17 is an inverting amplifier, and a preamplifier 11
It outputs 1q of signals with the opposite polarity and the same amplitude as the output of .

20 and 30 are both level control circuits, and operational amplifiers 21, 31 . It includes switches 22, 32, capacitors 23, 33, resistors 25.26, 35.36, and reference voltage 28.38. 41 is a switch, which includes two switches 41a and 41b; when one of the switches 41a and 41b is on, the other is off; when one is off, the other is on;
This switch 418 receives two signals of different polarities that are O-level controlled by two level control circuits 20 and 30.
．． 41b, the signals are taken out alternately and combined. 4
Reference numeral 2 designates an AC amplifier for amplifying the composite signal synthesized by the switch 41, which is applied via the coupling capacitor 43. 50 is a switch control circuit which receives a clock 51 and receives control signals 52, 53, 54 for turning on and off the switches 22, 32, 41a, 41b, respectively.
．． Outputs 55. A sampling AD converter 61 samples the output of the AC amplifier 42, performs AD conversion, and outputs a digital signal. 63 is a data processing circuit which receives the digital signal from the sampling AD converter 61, inverts the polarity of the negative direction component digital signal, processes it together with the positive direction component digital signal, and averages it by 1q. This eliminates noise and digitally reproduces the waveform of the input signal applied to the input terminal 13 of the preamplifier 11 without the influence of noise.

Next, the operation of the circuit configuration shown in FIG. 1 will be explained using FIG. 2 showing waveforms of various parts.

In FIG. 2, (a) is a clock 51. In synchronization with this clock 51, for example, a laser diode (not shown) is driven, and a signal obtained by optical-to-electrical conversion of the backscattered light of the fiber is transmitted to the front. is amplified by a stationary amplifier 11,
A waveform shown in (f) is obtained at the output terminal 15. The signal at the output terminal 15 is applied to an inverting amplifier 17 with a gain of 1 at 130, and the polarity of the signal is inverted to obtain a waveform with a polarity opposite to that of (, f) as shown in (CI>).

The switches 22 and 32 are controlled by control signals 52 and 53 shown in (d) and (e), respectively.
When the levels of the signals shown in f) and (q) become sufficiently low, switches 22 and 32 are turned on for a short time with their phases shifted. At this time, resistors 25 and 35
The output (f) of preamplifier 11 and inverting amplifier 17 applied to switches 41a and 41b, respectively, through
The output (q) of is accumulated and stored in capacitors 23 and 33, respectively.

This accumulated voltage and reference voltages 2B and 38 containing O volts are compared by operational amplifiers 21 and 31, respectively. As a result, the error voltage is amplified and applied to the operational amplifiers 21 and 31 via the resistors 26 and 36 and the switches 22 and 32 to the capacitors 23 and 33.
Since negative feedback is provided to capacitors 2j and 3,
The level (O level) of the signal accumulated in 3 becomes equal to the reference voltages 28 and 38, respectively. by this,
The O level of the signal is set. That is, the circuit including this negative feedback loop operates as a level control circuit.

Thus, the fully attenuated levels (O levels) of the signal waveforms shown in (f) and (q) are clamped to reference voltages 28 and 38, respectively, which are, for example, 0 volts.

Switches 41a and 41b control signals 54 and 5
The signal applied to the switch 41a and the signal applied to the switch 41b are switched every clock 51 (a>) to produce a composite signal (h) with the waveform shown in (f) and (g). ) is obtained.The switch 41 operates as a signal combining switch.

This composite signal (h) is applied to the AC amplifier 42 via the coupling capacitor 43. Here, since the composite signal shown in (h) is a composite of the waveforms shown in (f) and (g) that make the O level equal, the areas above and below the O level are equal, and the signal is amplified by the AC amplifier 42. Even when amplification is performed, highly accurate amplification is possible without causing level fluctuations.

If there is no negative feedback loop of the level control circuits 20 and 30, the composite signal applied to the AC amplifier 42 will have the same waveform area as shown in (k) on the positive side and the negative side. This results in a waveform that causes a shift in the O level at S. The waveform shown in FIG.

The data processing circuit 63 inverts the polarity of the signal that has passed through the switch 4'1b (see Figure 2).
)> Perform averaging processing. Therefore, the waveform represented by the digital value inside the data processing circuit 63 becomes as shown in FIG. 2 (j>), and high-speed averaging processing becomes possible.

It is clear that a transfer type switch as shown in FIG. 3 may be used as the switch 41 shown in FIG. 1.

When using an amplifier capable of obtaining both positive and negative polarities as an output as shown in FIG. 4 as the preamplifier 11, its output terminals 15a and 15b are connected to resistors 25 and 3, respectively.
5, the inverting amplifier 17 can be omitted.

[Effect of the invention] As is clear from the above explanation, according to the present invention,
Create two signals with different polarities from the repeated input signals, clamp the O level, take out the signals with different polarities alternately, combine them, accurately amplify them with an AC amplifier, sample them, and perform AD conversion. and convert it into a digital value. Here, since the polarity of the digital signal of one polarity is inverted and the averaging process is performed together with the digital signal of the other polarity to remove noise, the averaging process is twice as fast as in the conventional technology. The effect of this treatment is extremely large.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing one embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIGS. 3 and 4 are diagrams for explaining another embodiment. FIG. 5 and FIG. 6 are diagrams for explaining conventional examples. 11... Preamplifier 13... Input terminal 14.
... Light receiving element 15 ... Output terminal 17 ... Inverting amplifier 20.30 ... Level control circuit 21.31 ... Operational amplifier 22.32 ... Switches 25.26, 35.36 ... Resistor 28.38...Reference voltage 41...Switch 42...AC amplifier 43
~45...Coupling capacitor 49...Output terminal 50...Switch control circuit 51...Clock 52-55...Control signal 61...Sampling AD converter 63...Data processing circuit.

Claims (7)

[Claims] (1) Amplify the repeated input signal to obtain a first signal and a second signal with the same amplitude and opposite polarity as the first signal, and set the 0 level of the first signal to a predetermined value. clamp the 0 level of the second signal to a predetermined voltage, and obtain both signals from the clamped and repeated first signal and the clamped and repeated second signal. are taken out alternately each time to obtain a composite signal, the composite signal is amplified by an AC amplifier, the amplified composite signal is converted to a digital value, and the composite signal converted to the digital value is A signal processing method characterized in that data processing of the composite signal is performed by inverting the polarity of a digital value of a portion corresponding to the second signal. (2) preamplifying means for amplifying a repeated input signal and outputting a first signal and a second signal having the same amplitude and opposite polarity as the first signal; a first level control circuit for clamping the 0 level of the signal to a predetermined voltage; a second level control circuit for clamping the 0 level of the second signal to a predetermined voltage; After receiving a repeated first signal from the level control circuit and a repeated second signal from the second level control circuit, both signals are alternately passed through each repetition to generate a composite signal. an AC amplifier for amplifying the composite signal; an AD converter for converting the composite signal amplified by the AC amplifier into a digital value; and data processing means for receiving the value and inverting the polarity of the digital value of a portion of the composite signal corresponding to the second signal, and processing the data of the digitized composite signal. A signal processing device characterized by: (3) The preamplification means includes an amplifier for amplifying the repeated input signal and an inverting amplifier with a gain of 1, the output of the amplifier being the first signal, and the output of the amplifier being the first signal. 3. The signal processing device according to claim 2, wherein the output of the inverting amplifier that is input is output as the second signal. (4) The first level control circuit includes a first signal resistor for passing the first signal, and is connected to the output side of the first signal resistor to control the repeated input signal. a switch for extracting the 0 level; a capacitor for accumulating the extracted 0 level; and a reference voltage containing 0 volt for clamping the extracted 0 level accumulated in the capacitor. , an operational amplifier for comparing the extracted 0 level and the reference voltage; and a negative feedback loop connected between the output of the operational amplifier and the output side of the first signal resistor. 1st for
a feedback resistor, the second level control circuit is connected to a second signal resistor for passing the second signal, and an output side of the second signal resistor, and the second level control circuit is connected to the output side of the second signal resistor. A switch for extracting the 0 level of the returned input signal, a capacitor for accumulating the extracted 0 level, and a 0 volt for clamping the extracted 0 level accumulated in the capacitor. an operational amplifier for comparing the extracted 0 level and the reference voltage; and a negative feedback loop connected between the output of the operational amplifier and the output side of the second signal resistor. The second to configure
3. The signal processing device according to claim 2, further comprising a feedback resistor. (5) The signal processing device according to claim 2, wherein the signal synthesis switch means includes a transfer type switch. (6) The signal processing device according to claim 2, wherein the AD conversion means samples the composite signal amplified by the AC amplifier and converts it into a digital value. (7) The signal processing device according to claim 2, wherein the data processing means averages the digitized composite signal at least for the purpose of noise removal.