RU2800397C1 - Rms millivoltmeter - Google Patents

Abstract

FIELD: measurements.

SUBSTANCE: invention relates to fluctuation noise parameters measurement technique and can be used in any area where it is required to determine effective noise values. An RMS millivoltmeter comprising an input device, an instrumental transducer and an output device, the instrumental transducer is made in the form of a linear amplifier and a threshold device connected at its output with an operating threshold 1σ<U<3σ where σ is the RMS value of the noise at the input of the threshold device; a reference voltage source with a divider is introduced, the output of which is connected to the reference input of the threshold device, and at the output of the threshold device, a meter of the average frequency f of the threshold device responses from noise emissions exceeding the threshold, and a solver for determining the estimate of the measured quantity σ = U √ (1/2in(f₀/f)), where f₀ is the average frequency of the noise exceeding the zero level, constant for this system, and the output device included at the output of the solver is a decoder for outputting results to an external terminal, for example, a digital indicator. The threshold device is made in the form of an analogue comparator, and the division factor of the divider K=U_ref/U, where U_ref is the output voltage of the reference voltage source, and U is the threshold voltage of the comparator. The meter of average frequency f of threshold device actuations is made in the form of a pulse counter with a time setting device.

EFFECT: fast determination of the root-mean-square value of fluctuation noise when building miniature equipment, including portable and embedded equipment, operating in a wide range of climatic conditions.

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Description

The present invention relates to the measurement of fluctuation noise characteristics, in particular, to the technique for receiving weak pulsed signals, and can be used in the design and manufacture of receivers for location, communications and other areas.

It is known that knowledge of the noise dispersion is important for the correct construction of the signal thresholding mode [1].

Known technique for receiving weak optical signals using avalanche photodiodes [2]. There are also known ways to stabilize the avalanche mode of the photodiode, for example, by thermal compensation of the operating point of the bias voltage [3]. These solutions do not provide the maximum signal-to-noise ratio because they do not control this ratio.

The effective (rms) value of the electrical quantity is determined by standard laboratory instruments [4-6]. The technical and metrological principles adopted in them are feasible in stationary equipment, but do not provide the possibility of their application in miniature equipment in a wide temperature range.

The closest to the proposed technical solution is an RMS millivoltmeter [6], containing an input matching device, instrumental analog converters and an output analog square-to-linear voltage converter for the output data output device. This laboratory millivoltmeter has two converters on integrated instrumentation amplifiers based on wideband operational amplifiers. Two matched pairs of high-frequency Schottky diodes operating without bias were used as quads. This provided full-wave signal processing. Compared to the V3-48A serial millivoltmeter, the use of instrumental amplifiers and broadband op amps made it possible to simplify the device circuit and its adjustment, and expand the frequency band of the measured signals.

The structure of this millivoltmeter is implemented in a laboratory device with dimensions (without an external probe), 271×191×123 mm and a mass of 2.57 kg, operating in a narrow temperature range. Such equipment is unsuitable for embedding in miniature receiving devices, especially as part of portable communication systems, locations, etc.

The objective of the invention is to promptly determine the root-mean-square value of the fluctuation normal noise of receiving devices in the process of manufacturing and servicing miniature, including portable and built-in equipment, in a wide operational range with simple metrological support.

This problem is solved due to the fact that in a well-known rms millivoltmeter containing an input device, an instrumental converter and an output device, the instrumental converter is made in the form of a linear amplifier and a threshold device connected at its output with an operating threshold of 1σ<U<3σ, where σ is the rms the value of the noise at the input of the threshold device, and a reference voltage source with a divider is introduced, the output of which is connected to the reference input of the threshold device, and at the output of the threshold device, a meter of the average frequency f of the threshold device responses from noise emissions exceeding the threshold, and a solver for determining the estimate measured value where f ₀ is the average frequency of the noise exceeding the zero level, constant for this system, and the output device included at the output of the solver is a decoder for outputting results to an external terminal, for example, a digital indicator.

The threshold device is made in the form of an analog comparator, and the division factor of the divider is K=U _op /U, where U _op is the output voltage of the reference voltage source, and U is the threshold voltage of the comparator.

Meter average frequency f actuations of the threshold device is made in the form of a pulse counter with setting the accumulation period T time setting device.

The operating principle of the device is based on the dependence of the average frequency f of crossing the threshold U by fluctuation noise emissions [7, 8], which obeys the normal distribution

Where - average frequency of noise crossing the zero threshold;

R(τ) is the noise correlation function determined by the frequency response of the receiving-amplifying path.

The frequency f ₀ can be preliminarily determined at the threshold level U=0 by counting the number No of zero crossings by the noise during the time T' and calculating the frequency f ₀ using the formula f ₀ =N ₀ T. This parameter is constant for this device and does not require verification at each measurement a.

From relation (1) follows the expression for calculating a used in the present invention

In FIG. 1 shows a block diagram of the device.

In FIG. 2 - version of the threshold device with a reference voltage source.

In FIG. 3 is a graph of the determination error as a function of the Wo ratio.

A quadratic millivoltmeter (Fig. 1) includes an input device 1 for matching the circuit with signal and noise sources and an amplifier 2 connected in series at its output, a threshold device 3, a counter 4 and a decision device 5 with an output device 6. At the reference input of the threshold device 3, in series the reference voltage source 7 and the voltage divider 8 are switched on. The time setting device 9 is switched on at the control input of the counter 4.

At the beginning of work, the reference input of the threshold device 3 from the reference voltage source 7 is supplied with voltage U=U _pore =U _op /K, where K is the division factor of the divider 8. Then the time setting device 9 is turned on, which opens the counter 4 for time T. At the moments of intersection noise emissions from the output of the amplifier of the set threshold U, the threshold device is triggered, increasing the state of the counter by one. At the end of the interval T, the counter accumulates the sum of N operations, which enters the decision device 5. Based on the values of U, f=N/T and the known frequency f ₀ , set previously for this equipment, an estimate of the measured value is formed in the decision device 5 issued to the output device 6.

The proposed technical solution can be built into the standard structure of the photodetector and allows you to measure the noise intensity at the output of the linear path in the working composition of the device during its operation.

In FIG. Figure 2 shows the structure of a threshold device that determines the accuracy of measurements based on an analog comparator 3 with a reference voltage source 7 and a divider 8.

Existing high-speed sensitive comparators provide operation frequency up to (10-50) MHz [10, 11].

Reference voltage sources at a nominal output voltage of 1.2 V and an accuracy of its maintenance of ±(0.1-0.2)% have a temperature drift of (8-30)⋅10 ^-1 %/deg [12-14]. As follows from expression (2), the error in setting the reference voltage U is included in the measurement error a with the same relative value. Therefore, for existing sources, the error is also (0.1-0.2)%, but this error can be taken into account when calibrating the solver.

The error in maintaining the ratio f ₀ /f can have a significant effect on the measurement error. This error depends on the threshold level U relative to o. On the graph of Fig. 3 shows this dependence with an error in determining f ₀ /f equal to 0.1%. In this case, with a ratio of U/σ<0.5, the measurement error increases to 0.4% or more, and with a ratio of U/σ>1.5, the measurement error, on the contrary, decreases to (0.1-0.05)% .

When designing a millivoltmeter, it is necessary to minimize the error associated with the Poisson nature of the sequence of exceeding the threshold by noise [8]. According to this statistical distribution, a random number N has a mathematical expectation M _N =N, variance D _N =N.

standard deviation When creating equipment, the condition is accepted where X=(2-4) - allowable relative deviation of the random variable N from the average value Mn; - confidence coefficient characterizing the probability of such a deviation. That is where does the requirement come from

Example 1

N>(3/0.01) ² =90000.

The accumulation period T depends on the selected amount N and the threshold/noise ratio, which determines the average frequency of noise exceeding the threshold f.

Example 2

Ratio U/σ=2; f ₀ \u003d 10 ⁷ 1 / s. Average frequency (1)

Accumulation period Т=N/f=90000/1353353=0.067 s.

Consequently, a minimum measurement error (0.05-1)% of measurement is provided, sufficient for the operational assessment of the noise level of receiving-amplifying devices in a wide temperature range, both in a stand-alone version of the device and as part of functional complexes.

Analog instrumental procedures do not contain nonlinear functional transformations, and are implemented on the existing element base in miniature volumes with reliable reproducibility and stability, as well as with simple metrological support.

The proposed device has a minimum measurement time. With an acceptable error in determining a within (0.1-1)%, the measurement time is T<0.05-0.1 s.

Thus, the device provides a solution to the problem - prompt determination of the root mean square value of the fluctuation normal noise of receiving devices during the production and maintenance of miniature, including portable and embedded equipment, in a wide operational range with simple metrological support.

Information sources

1. Vilner V.G. Evaluation of the possibilities of a light-location pulsed range meter with accumulation. - M.: Photonics. 2007. No. 6. - With. 22-26.

2. I.D. Anisimova and others. Ed. IN AND. Stafeeva. Semiconductor photodetectors receivers. Ultraviolet, visible and near infrared ranges of the spectrum. - M.: Radio and communication, 1984 - 216 p.

3. Patent of the Russian Federation No. 2 248 670. A device for switching on an avalanche photodiode in an optical radiation receiver.

4. Nasonov B.C. Handbook of radio measuring instruments. - M: Soviet radio, 1976, v.1., 234 p.

5. F.V. Kushnir. Electroradio measurements.: Uch. allowance for universities. - L., Energoatomizdat. Leningrad. department, 1983 - 320 p.

6. D. Molokov. High frequency RMS millivoltmeter. Radio magazine. No. 5, 2019 - p. 14-21 - prototype.

7. Vilner V.G. Design of threshold devices with noise threshold stabilization. - Optical-mechanical industry, 1984, No. 5, p. 39-41.

8. Tikhonov V.I. Emissions of random processes. Ch. ed. Phys.-Math. lit., 1970, - p. 392.

9. Filachev A.M., Taubkin I.I., Trishenkov M.A. Solid state photoelectronics. Physical bases. Moscow, Fizmatgiz. 2007, - p. 345.

10. High speed comparator TL714C. Texas Instruments. Datasheet 2003.

11. High speed comparator e MAX941/MAX942/MAX944. MAXIM. Datasheet 2004.

12. Reference voltage source ADR3412. analog devices. Datasheet 2010.

13. Reference voltage source MAX6023EVT12. MAXIM. Datasheet 2012.

14. LM4040AIM3-2.5/NOPB voltage reference, Texas Instruments Datasheet 2016.

Claims (3)

1. An RMS millivoltmeter containing an input device, an instrumental transducer and an output device, characterized in that the instrumental transducer is made in the form of a linear amplifier and a threshold device connected at its output with an operating threshold of 1σ<U<3σ, where σ is the RMS value of the noise at the input threshold device, and a reference voltage source with a divider is introduced, the output of which is connected to the reference input of the threshold device, and at the output of the threshold device, a meter of the average frequency f of the threshold device responses from noise emissions exceeding the threshold, and a decisive device for determining the estimate of the measured value where f ₀ is the average frequency of the noise exceeding the zero level, constant for this system, and the output device included at the output of the solver is a decoder for outputting results to an external terminal, for example, a digital indicator. 2. RMS millivoltmeter according to claim 1, characterized in that the threshold device is made in the form of an analog comparator, and the division factor of the divider is K=U _op /U, where U _op is the output voltage of the reference voltage source, and U is the threshold voltage of the comparator. 3. RMS millivoltmeter according to claim. 1, characterized in that the average frequency meter f of threshold device operations is made in the form of a pulse counter with a time setting device.

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