RU2022278C1 - Device for measuring instant frequency - Google Patents

Abstract

FIELD: radio engineering. SUBSTANCE: device for measuring instant frequency has high frequency amplifier, "up" frequency converter, which has mixer, rejection filter and heterodyne connected in series. The heterodyne is connected with the second input of mixer. Device also has high frequency divider, the first and the second frequency discriminators with detector sections, subtraction and addition unit, comparator unit, analog-to-digital converter unit, arithmetical-logic unit. EFFECT: improved precision of measurement. 4 dwg

Description

 The invention relates to radio engineering and can be used as a digital meter of instantaneous frequency of a radio signal.

 Currently, the problem is the construction of an instantaneous frequency meter with the required measurement accuracy in a given range, for example from 10 to 1000 MHz, with a measurement error of 0.1-0.01%.

 Known meters instantaneous frequency (MIC) for early warning of radar exposure (see US patent N 4053841, N 4110700).

 These devices are designed on the basis of frequency discriminators (BH) with delay lines (LH) with subsequent signal processing.

 The task of determining the frequency signal is to calculate the phase difference based on the measured voltages at the BH outputs.

 The disadvantages of these devices is a large number of BHs to achieve the necessary accuracy of frequency measurements, which significantly reduces the reliability of the device and increases its cost.

 The closest in technical essence is a digital meter of instantaneous signal frequency (see the abstract of Bauman R, "Digital instantaneous frequency measurement for Ewreceivers -" Microwave I., 1985, 28, No. 2, published in Russian translation in the bulletin of EI "Radio engineering microwave" , 1986, N 9, p.11, Fig. 2), containing a series-connected bandpass filter, a high-frequency amplifier - UHF, an amplifier-limiter, a high-frequency power divider, a threshold detector, a block of frequency discriminators (BH) and detectors, an analog- digital frequency code conversion.

 The principle of operation of the meter is to determine the frequency of a high-frequency (HF) signal by measuring the phase on a fixed section of the transmission line.

The RF signal at the input of the discriminator is divided into two components, one of which is delayed. Then both components go to the inputs of the phase-analyzing part, consisting of quadrature bridges and a ninety-degree Schiffman phase shifter. The outputs of the analyzer are offset from each other by ⁹⁰ ° and their amplitudes vary in proportion to the frequency.

 Next, the signal is detected and fed to the inputs of the comparators. Such a frequency discriminator scheme determines the frequency value in the form of a four-bit word. Digital processing of video signals can be carried out either by quantizing them to K levels, or by determining the polarity of the converted video signals. For a twelve-bit representation of the frequency of the RF signal, the digital instantaneous frequency meter (MIC) has five BHs with a multiplicity of the delay line length LZ 1: 4. In the digital correction circuit, the two lower-order bits of the frequency code are corrected by the two high-order bits of the BH code having a longer LZ. The adjustment process is carried out sequentially for all BHs, except for the most accurate (i.e., having the greatest delay).

However, this device has disadvantages in that a certain amount of BH is necessary to achieve the required accuracy in determining the frequency code. So, for example, an unambiguous determination of the frequency is possible only within the limits of the change in the phase angle θ from 90 to 360 ^° . Moreover, it is obvious that it is difficult to obtain a satisfactory accuracy in measuring the frequency in the frequency band of 1000 MHz using one BH stage because of the very tight tolerance on the error of the phase meter. To obtain the required accuracy of frequency measurement, 5 BH stages with digital processing by determining the polarity of video signals are necessary. At the same time, the hardware composition sharply increases both in the analog block and in the digital signal processing block, the requirements for the parameters of microwave nodes are increased due to the stitching of a large number of processing channels.

 The purpose of the invention is to reduce the composition of the equipment without compromising accuracy when measuring the Doppler frequency of the signal.

 To achieve the goal, a device for measuring the instantaneous frequency of a high-frequency signal, comprising a high-frequency amplifier, a high-frequency power divider, first and second frequency discriminators with detector sections, an analog-to-digital converter, wherein the first and second outputs of the high-frequency power divider are connected to the inputs of the first and second frequency discriminators accordingly, the input of the high-frequency amplifier is the input of the device, further comprises a summing and subtracting unit, a compar unit orov, an arithmetic-logical unit, an Up frequency converter, containing a series-connected mixer, the input of which is the converter input, and a notch filter, the output of which is the converter output, a local oscillator connected to the second input of the mixer, the output of the high-frequency amplifier connected to the input frequency converter "Up", the output of which is connected to the input of a high-frequency power divider, the first, second, third, fourth outputs of the first and second frequency discriminators are connected with the corresponding inputs of the signal summing and subtracting unit, the first, second, third and fourth outputs of which are connected to the corresponding inputs of the comparators block, the information output of which is connected to the first information input of the arithmetic-logical block, the output of which is the output of the device, the second information input is connected to the output of an analog-to-digital converter, the first, second inputs of which are connected to the fifth and sixth outputs of the summing and subtracting unit, respectively.

 Comparative analysis with the prototype shows that the claimed device is characterized by the presence of new blocks and new connections, the combination of which allowed us to achieve the specified accuracy of the receiver parameters with fewer discriminators, which gives significant savings in microwave components, low-frequency amplifiers and processing channels. Thus, the claimed device meets the criteria of the invention of "Novelty."

 A comparative analysis showed that the above blocks are introduced into the device for measuring the instantaneous frequency of the signal in the indicated connection and exhibit new properties, which leads to a significant reduction in hardware costs while maintaining the specified accuracy of the device when measuring the Doppler frequency. This allows us to conclude that the technical solution meets the criterion of "significant differences".

 In FIG. 1 shows a block diagram of the proposed device. The device contains a serially connected high-frequency amplifier 1, an up-converter 2, comprising a mixer 3 in series, the input of which is the input of the frequency converter 2, a notch filter 4, the output of which is the output of the frequency converter, and a local oscillator 5, the output of which is connected to the second the input of the mixer 3, the output of the up-converter 2 is connected to the input of a high-frequency power divider 6, the first and second outputs of which are connected to the corresponding inputs of the first and of frequency discriminators 7 with detector sections, the first, second, third and fourth outputs of each of the two discriminators are connected to the corresponding inputs of block 8 of the adder and subtracter, the first, second, third and fourth outputs of which are connected to the corresponding inputs of block 9 of the comparators, and the fifth and the sixth outputs of block 8 are connected to the corresponding inputs of block 10 of analog-to-digital converters, the first and second information outputs of which are connected to the second and third information inputs of arithmetic cally-logic unit 11, first information input coupled to a data output unit 9, the information output unit 11 is an information output device.

 The proposed device, according to figure 1, works as follows.

 The input signal, which is a radio signal of the Doppler frequency (frequency range from 10 to 1100 MHz), is fed to the input of the high-frequency amplifier 1, which serves to interface the unit 2 of the frequency converter with other devices in amplitude. The actual adjustment range is 60 dB. Next, the signal enters the mixer 3, which, together with the local oscillator 5, carries out the transfer of the frequency spectrum 10 ... 1100 MHz to the range 4000 ... 5000 MHz. Filter 4 serves to highlight the upper sideband of the frequency conversion and suppress the lower sideband. Its main feature is a steep slope of the frequency response at a cutoff frequency.

Next, the signal is fed to the in-phase three-decibel power divider 6, which divides the input signal by power into two BH stages (see Fig. 2,3). To ensure the unambiguity of measurements (θ = 360 ^° ), the delay line in the BH of the first stage is chosen equal to the wavelength with a frequency of 1000 MHz, i.e. the full period of phase change of 360 ^about corresponds to a given band of measured frequencies. Accordingly, the delay line in the second stage BH is twice as large, i.e. θ ₂ = 2 θ ₁ .

 In FIG. Figures 2 and 3 show the totality of dependencies realized at the outputs of two stages of BH 7.

; U₂= cos²

; U₃= sin²

; U₄= cos²

;
U₅= sin²

; U₆= cos²

; U₇= sin²

; U₈= cos²

где θ ₁ и θ ₂ - фазовые углы, несущие информацию о частоте ВЧ-сигнала на входе МИЧ.The amplitude of the detected signal is a function of the frequency of the input microwave signal. Thus, at the input of the first and second BH 7, video signals are formed, which can be simplifiedly represented as:
U ₁ = sin ²

; U ₂ = cos ²

; U ₃ = sin ²

; U ₄ = cos ²

;
U ₅ = sin ²

; U ₆ = cos ²

; U ₇ = sin ²

; U ₈ = cos ²

where θ ₁ and θ ₂ are phase angles carrying information about the frequency of the RF signal at the input of the MIC.

- sin²

= cosθ₁
б) sin

- cos

= sinθ₁.These signals are fed to the input of block 8 summing and subtracting signals. The first four dependencies are converted to:
a) cos ²

- sin ²

= cosθ ₁
b) sin

- cos

= sinθ ₁ .

- sin²

= cosθ₂
е) sin

- cos

= sinθ₂
График преобразованных функций имеет вид, как показано на фиг.4.c) cos θ ₁ + sin θ ₁
d) cos θ ₁ -sin θ ₁
Using the following four function dependencies:
d) cos ²

- sin ²

= cosθ ₂
e) sin

- cos

= sinθ ₂
The graph of the converted functions has the form, as shown in figure 4.

 The entire range in phase (frequency) is divided into eight parts, each of which can be uniquely determined using the Johnson code, for which it is enough to analyze the signal from the point of view of the transition of functions through zero. If the signal is in the positive area, then the value of the logical "0" is accepted, if in the negative - the logical "1". Thus, it is obvious that the frequency is determined with an accuracy of 1/8 of the MIC range of operation.

или ± 80 мГц _→

, где f_в - верхняя граничная частота измеряемого сигнала;
f_н - нижняя граница частоты измеряемого сигнала.Thus, the first four video signals (a-d) are fed to the inputs of the analog comparators of unit 9, at the inputs of which a four-digit Johnson code (memory code) is generated, which is converted by the arithmetic-logical unit 11 into a three-digit binary code with a low order weight of ± 22.5 ^° _ →

or ± 80 MHz _ →

where f _in - the upper cutoff frequency of the measured signal;
f _n - the lower limit of the frequency of the measured signal.

The phase angle θ ₂ changes two times faster than θ ₁ , therefore, within the zones (see Fig. 4, the axes are marked with a double line), which allow us to uniquely determine θ ₂ , and therefore the signal frequency within this zone. In zones I (0001), III (0111), V (1110), VII (1000), the angle θ ₂ and frequency are determined by the characteristic depicted by a dashed double line. In these sections, the angle θ ₂ is determined by measuring the amplitudes of the converted signals sin θ ₂ and cos θ ₂ by the quantization method, i.e. the two remaining video signals cos θ ₂ and sin θ ₂ from the output of block 8 are fed to the inputs of block 10 of the ADC, where they are converted into a digital binary direct code.

Given that the frequency vector of the first BH unit 7 rotates twice as fast as the frequency vector in the second BH 7 (due to the doubled delay line), we can calculate the angle θ ₂ with great accuracy by taking arсcos θ ₂ and arcsin θ ₂ (block 11). It is advisable to make measurements on the signal with a higher amplitude change rate in order to reduce errors that increase near the extrema of the functions cos θ ₂ and sin θ ₂ .

 The desired function is selected by a digital multiplexer, which is controlled by a three-digit frequency code obtained after processing the video signal of the first BH7. The frequency is calculated using the EEPROM of block 11 with 11-bit address inputs, which allows to minimize the error by writing to the EEPROM all deviations from the theoretical frequency response characteristics that may differ from each other at different frequency discriminators.

 Thus, using the voltage comparators of unit 9, determining the incoming signal is more or less zero, you can immediately generate a frequency code, the weight of the least significant bit of which, for example, with a band of 1256 MHz, is 160 MHz.

 The second BH7 has a delay line with a length twice as long as the first, and its frequency response varies from zero to a certain value according to the law cos and sin inside the zones obtained by the first discriminator. Converting the analog signal into a digital code using ADC 10 and dividing sin θ / cos θ by block 11, we obtain tan θ. Further, knowing the zone in which the signal is located and taking arctan θ, we can calculate the frequency of the signal under study using the formula.

, θ₂= arccos

, θ₂= arcsin

где Δ l - длина линии задержки в ЧД;
U - измеренное значение напряжения, получаем
λ =

=

f =

=

=

Соответственно для нечетных зон:
f′ =

для четных зон:
f″ =

где с=3˙10⁸ м/с;
f',f'' - частота в пределах измерения зоны. Искомая частота находится
f_х=F+f' - для нечетных зон,
f_х= F+f'' - для четных зон, где F - нижняя частота зон, определяемая на первом этапе.Given that θ =

, θ ₂ = arccos

, θ ₂ = arcsin

where Δ l is the length of the delay line in BH;
U is the measured voltage value, we obtain
λ =

=

f =

=

=

Accordingly, for odd zones:
f ′ =

for even zones:
f ″ =

where c = 3˙10 ⁸ m / s;
f ', f''- frequency within the zone measurement. The desired frequency is
f _x = F + f '- for odd zones,
f _x = F + f '' - for even zones, where F is the lower frequency of the zones, determined at the first stage.

 An analog-to-digital conversion of the obtained functions is performed using an 8-bit high-speed ADC 1107PV2, included in a typical scheme.

 The frequency calculation unit performs the calculation operation using multiplexers and a ROM type 556PT7 with a capacity of 2K bytes.

 The inputs X1 of the multiplexers receive information in parallel binary code from the ADC 1, and the inputs X2 from the ADC 2.

 Multiplexers are controlled by a signal from the least significant digit (MLM) of the zone number. In addition, all three bits of the zone number go to the higher address bits of the ROM.

 The address inputs A0 ... A7 receives information from the outputs of the multiplexers.

When writing a program for the EPROM, it is necessary to divide the entire memory into 8 pages, which really happens with the help of a three-digit zone number. In even pages at the desired addresses, it is necessary to write the frequency corresponding to the values of sin θ ₂ , and in odd pages - cos θ ₂ (see figure 4).

 Depending on the level of the MLR of the zone number, the outputs of the ADC1 and ADC2 are connected to the address inputs of the EPROM. At the same time, the zone number determines the desired ROM memory page.

 After the time required to decrypt the address, the contents of the memory cell corresponding to the one that came to the input at the address, i.e. information about the frequency of the input signal.

 The frequency at the MIC output is represented in parallel binary 12-bit code. The weight of the least significant bit is 0.5 MHz. Each word changes with a sampling rate.

 The first information appears at the output of the block 0.8 μs after the arrival of the signal "Permission for work" with RBPP at the input of the block.

 The repetition period of clock pulses T = 0.5 μs.

 Structurally, the device is made in the form of separate complete functional blocks: the Up frequency conversion block, the analog signal processing block, and the digital signal processing block.

 The high-frequency input amplifier 1 is assembled on four p-i-n-diodes and has a transistor linearizer in the electronic control circuit, which allows you to smoothly adjust the level of input signals for further processing.

 The mixer 3 is assembled on strip transmission lines and microwave diodes with Schottky barriers.

 Heterodyne 5 is assembled on a bipolar transistor using strip technology. The filter 4 is made on microstrip transmission lines and resonators.

 High-frequency nodes are made in the form of microassemblies of thin-film technology. (An example of the implementation of high-frequency nodes, see the literature: Semiconductor devices in microwave circuits. Edited by M. Howes, D. Morgan. M.: Mir, 1979; I.V. Lebedev. Equipment and devices for microwave frequencies. L., 1961 .

 A phase detector containing SDM, H01, H02, H03, CH and load diodes, is made in the form of a single, complex, integrated assembly. The delay lines in stages 1 and 2 of the black hole are based on coaxial cables of the type RK-50-2-21, dielectric material with ε = 2.0.

 The digital signal processing unit is based on operational amplifiers 140 UD6, comparators 521CA1 and ADC 1107PA2 and ППЗУ 556РТ7. The code conversion unit is executed on the logic of the 530, 533 series, a register of type 533IR16 is applied. Multiplexers type 530KP11.

 The structure of the central control unit includes the following nodes: analog processing unit; Johnson code conversion node; ADC unit frequency calculation unit (see electrical circuit diagram E350.020E3 and technical description 350.000 T0).

 Such a construction of the device circuit allows using only two BHs to obtain an acceptable error (from 0.2 to 1.5 MHz) in the frequency measurement. In addition, the proposed device for instant measurement of a high-frequency signal has the following advantages in comparison with the known: reduction in the overall dimensions of the device; reduction in energy consumption; improving the manufacturability of the design.

Claims (1)

 DEVICE FOR MEASURING INSTANT FREQUENCY, comprising a high-frequency amplifier, the input of which is connected to the input terminal of the device, a high-frequency power divider, first and second frequency discriminators with detector sections, an analog-to-digital converter, the first and second outputs of the high-frequency power divider connected to the inputs of the first and the second frequency discriminators, respectively, characterized in that, in order to simplify the device without compromising accuracy in measuring the Doppler frequency, the device o additionally contains a summation and subtraction unit, a comparator unit, an arithmetic logic unit, an up-converter, containing a series-connected mixer, the input of which is the input of the converter and a notch filter, the output of which is the output of the converter, a local oscillator, the output of which is connected to the second input mixer, and the output of the high-frequency amplifier is connected to the input of the up-converter, the output of which is connected to the input of a high-frequency power divider, first, w a swarm, the third and fourth outputs of the first and second frequency discriminators are connected to the corresponding inputs of the summation and subtraction unit, the first, second, third and fourth outputs of which are connected to the corresponding inputs of the comparators block, the information output of which is connected to the first information input of the arithmetic-logical block, the output which is connected to the output of the device, the second information input of the arithmetic logic unit is connected to the output of the analog-to-digital converter, the first and second inputs which are connected to the fifth and sixth outputs of the summation and subtraction unit, respectively.

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