Method for measuring noise ratio

Abstract

FIELD: radio engineering.SUBSTANCE: invention can be used to evaluate and control the noise figure of a wide range of devices. The method for measuring the noise figure comprises stages in which the losses at the input and output of the measured device are measured, after which the device is connected to the test setup, the noise power is measured at the input of the measuring device of the test setup, the number of averaging used is determined, the output noise power of the test setup is measured after the power supply of the measured device is turned on, and the total noise power is measured with a harmonic signal of the generator exceeding the level of the output noise power of the test setup. Next, the gain of the device being measured and the signal-to-noise ratio are determined based on the results of the measurements obtained to determine the noise figure of the device being measured, taking into account the number of averagings used.EFFECT: using a single circuit for connecting measuring instruments, increasing the accuracy and repeatability of measurements.1 cl, 8 dwg

Description

[0001] The invention relates to radio engineering and can be used to evaluate and control the noise figure of a wide range of devices (including low-noise amplifiers, mixers, preselectors, intermediate frequency paths and other components of the analog path of receiving devices) during the development of parameters on prototypes, acceptance tests of prototypes and serial products, incoming inspection, etc. Additionally, such characteristics as the signal-to-noise ratio, sensitivity level and gain can be evaluated.

[0002] There are three classical methods for measuring the noise figure (NF) of radio-technical devices: Y-factor, cold source, and power doubling [1]. These methods involve sequentially measuring the gain (GF) of the device under test (DUT), the NF of the measuring device (MD, e.g., spectrum analyzer, etc.), and additional calibration, which usually requires reconnecting the test setup. Due to the need to evaluate a large number of parameters with various settings and test setup configurations, these methods are often used for manual measurements. Manual measurements are characterized, firstly, by high time costs. Secondly, a large number of reconnections during manual measurements is associated with a significant increase in the influence of the human factor on the final measurement error and repeatability of results. To minimize the impact of the above-mentioned disadvantages, automation of measurements is used.

[0003] Automated methods for measuring the noise level are known, which require the use of various additional equipment in the test setup: external preamplifiers, control units, noise receivers and other technological devices.

[0004] In most sources, for example, in the patent US 6714898, H04B 15 / 00, G06F 15 / 00, a noise signal from a noise source, or a harmonic signal from the output of a signal generator, or the port of a vector network analyzer (VNA) is fed to the input of the DI. For example, in the application US 20050137814, G01R 29 / 26, a spectrum analyzer (SA) or VNA in patents US 10371733, GO1R 29 / 26, GO1R 27 / 28 and US 7038605, H03M 1 / 8, GO1R 29 / 26 are used as the DI.

[0005] US patents 11815540, G01R 29 / 26, H03F 3 / 19, US 6714898, H04B 15 / 00, G06F 15 / 00 propose the use of highly specialized equipment designed to accelerate and minimize measurement error: programmable signal generators, noise sources, highly specialized signal analyzers, VNAs with an additional signal measurement option, and various technological devices. This complicates and increases the cost of the test setup due to the additional components (preamplifiers, switches on load boards, etc.), which also contribute to measurement error.

[0006] Publication US 20050137814, G01R 29 / 26, describes a method for measuring the noise level of electronic components and receiver assemblies based on the Y-factor method. It proposes using an AS as a measurement device. Instead of using a noise source, embodiments of the invention involve incorporating a programmable arbitrary waveform generator (AWG) into the test setup, generating a quasi-white Gaussian noise signal or another arbitrary waveform. In some embodiments of the proposed method, the AWG and receiver are incorporated into an automated test setup, and measurements of noise signal parameters at various stages are performed by controlling RF switches on a load board.According to this method, the noise floor calculation is performed in four stages: measuring the "cold" and "hot" noise power of the test setup without the device under test, and measuring the "cold" and "hot" noise power of the test setup with the DUT. Using the obtained values ​​and the excess noise ratio (ENR), one can find the gain of the DUT, the spectrum analyzer noise floor, and the total noise floor of the test setup, which are used to calculate the noise floor of the device under test using the Friis formula [1]. This measurement method recommends using averaging, and the dependence of the standard deviation of the measured power of the "hot" and "cold" sources on the number of averagings used is given. To ensure repeatability of the results, the need for impedance matching at the input and output of the device under test is indicated. Synchronization of the arbitrary waveform generator with the receiver can be used for the same purposes.To achieve accurate results when measuring the noise level, it is recommended that the noise level of the receiver be significantly lower than the noise level of the device under test. To ensure this, a low-noise preamplifier is installed between the speaker and the device under test in the test setup. In the implementation under consideration, a programmable arbitrary waveform generator generates a noise level close to the sum of the noise level and the gain of the device under test. It is recommended that the noise level be greater than 10 dB to ensure a sufficient difference in the output power measured by the receiver between the on and off states.

[0007] The disadvantages of the described method are the need for additional equipment (in this case, a programmable arbitrary waveform generator, a load board with radio frequency switches), which complicates the test setup, which affects the measurement error, as well as the lack of justification for the applicability limits of this method.

[0008] Another method, according to US patent 11815540, G01R 29 / 26, H03F 3 / 19, uses a specialized noise power meter / receiver as a measurement device. The noise power meter / receiver uses cross-correlation analysis of the output signals of two independent channels to measure noise power. The output signals represent the sum of the total noise of the DUT for both channels and the intrinsic noise of each measurement channel. When implementing this method of noise figure measurement, it is necessary to additionally measure the gain using a different test setup configuration.

[0009] The disadvantage of this method is the use of a highly specialized noise measurement receiver, as well as the need to reconnect the test setup when performing additional gain measurements or adding a controlled noise source. There is also a risk of cross-correlation collapse, which will distort the noise floor estimate of the device being measured.

[0010] List of explanatory graphic materials:

[0011] Fig. 1. – enlarged block diagram representing the sequence of actions of the prototype method;

[0012] Fig. 2 – diagram of a test setup for measuring the noise figure, implementing the prototype method;

[0013] Fig. 3 – a block diagram illustrating the sequence of operations of the proposed method;

[0014] Fig. 4 – graph of the dependence of the standard deviation (SD) of the noise power on the sweep time and the number of averaging (average count);

[0015] Fig. 5 – graph of output power distribution P out ;

[0016] Fig. 6 – graph of the dependence of the difference between the overestimated gain of the measured device and KU IU from the signal-to-noise ratio (SNR);

[0017] Fig. 7 – output power comparison graph;

[0018] Fig. 8 – connection diagram of the measured device for measuring the noise figure using the proposed method.

[0019] The closest in technical essence to the proposed method is the noise factor measurement method presented in [2], adopted as a prototype.

[0020] The prototype method is illustrated by the diagram shown in Fig. 1 and includes the following operations.

[0021] In the first step (“Evaluation of Test Setup Requirements”, Fig. 1), in general, for different connection schemes and different types of devices under test, in order to select a suitable test setup configuration, the required setting of the input and output attenuators and preamplifier is determined, the noise figure of the vector network analyzer, the 1 dB gain compression point of the VNA (either according to the specification or by additional measurement) and the gain and 1 dB gain compression point of the device under test are estimated.

[0022] At the second stage of calibration (in this description of the prototype, calibration should be understood as the process of measuring and accounting for losses at the input and output of the DUT) (“Test Setup Calibration”, Fig. 1), a large number of reconnections are performed. First, when calibrating the power of the transmit and receive ports of the VNA (“calibrating the power of the transmit and receive ports of the VNA, Fig. 1), the attenuation value of the input attenuator [2] is selected. Next, an input attenuator and a power meter (not shown in Fig. 1), connected in series, are connected to the transmit port of the VNA, and the output signal power is calibrated. Then, a preamplifier (not shown in Fig. 1) is connected to the receive port of the VNA. If it is necessary to improve the matching, an output attenuator is connected to its input. The condition under which the noise figure of the device under test can be measured is determined by the fact that the noise figure of the receive port should be a maximum of 10 dB higher than the gain of the device under test.Therefore, a preamplifier with known gain and noise floor is selected to reduce the impact of the VNA noise figure on the final result. Next, the power meter (not shown in Fig. 1) is disconnected from the test setup, and the input attenuator, output attenuator (if present), and preamplifier are connected in series. The VNA receive port power is calibrated. This completes the power calibration of the VNA transmit and receive ports and the calibration of the input and output losses of the DUT ("Calibrating Input and Output Losses of the DUT," Fig. 1).

[0023] In the third step of VNA transmit and receive port noise calibration ("VNA transmit and receive port noise calibration", Fig. 1), the following reconnection of the test setup is required: disconnect the output attenuator from the input attenuator and connect a 50-ohm load to the input of the output attenuator, or, if one is absent, directly to the preamplifier (not shown in Fig. 1). After this, the VNA receive port noise calibration is performed by measuring the NS value of the VNA receive port. Noise calibration at the VNA transmit port output is performed after disconnecting the 50-ohm load and connecting the input and output attenuators. This completes the VNA transmit and receive port noise calibration step.

[0024] Next, at the fourth stage of attenuation calibration (“Attenuation Calibration”, Fig. 1), in order to correctly calculate the noise power at the input of the device being measured, the difference between the attenuator values ​​at the input at the previous stages of calibration and at the measurement stage is taken into account.

[0025] After completing the calibration steps, the DUT is connected to the test setup ("DUT Setup", Fig. 1). In the next step ("Measuring the Total Power and Gain of the DUT", Fig. 1), the total noise power of the test setup is measured at the VNA receiving port using the data from the root mean square (RMS) and average gain (AVG) detectors and the gain of the device under test. Then, in the "Calculating the DUT Gain" step (Fig. 1), the noise figure of the device under test is calculated based on the measured parameters (the output power of the VNA transmitting port during calibration, the total power of the test setup, and the gain of the DUT).

[0026] If significant fluctuations are visible on the graph of the dependence of the KS on the frequency, a decision is made to check the mismatch ("Check the mismatch?", Fig. 1). To evaluate the mismatch, S-parameter measurements are additionally performed in a separate test setup ("Changing the test setup for measuring S-parameters", Fig. 1). If necessary, in the next step "Selection of the output attenuator value" (Fig. 1), it is possible to select an attenuator from 3 to 10 dB and connect it to the output of the device under test, which will lead to the need to repeat some calibration steps ("Calibration of the test setup", Fig. 1).

[0027] When replacing the measuring device (“Replacing the measuring device?”, Fig. 1) and there is no need for recalibration (recalibration means repeating the calibration steps, starting from the “Test setup calibration” step, Fig. 1) (“Recalibration?”, Fig. 1), the measurement process is repeated from the “Installing the measuring device” step (Fig. 1).

[0028] Fig. 2 shows a diagram of a test setup implementing the prototype method, where the following designations are introduced:

[0029] 2 – input attenuator (In. ATT);

[0030] 3 – measured device (MD);

[0031] 4 – output attenuator (Output ATT);

[0032] 6 – power supply (PS);

[0033] 7 – personal computer (PC);

[0034] 8 – vector network analyzer (VNA);

[0035] 8.1 – vector network analyzer transmission port;

[0036] 8.2 – vector network analyzer receiving port;

[0037] 9 – preamplifier.

[0038] The test setup contains a vector network analyzer 8 with a transmit port 8.1 and a receive port 8.2. The transmit port 8.1 is connected via an input attenuator 2 to the first input of the measured device 3, the output of which is connected via an output attenuator 4 to the first input of the preamplifier 9, the output of which is connected to the receive port 8.2 of the VNA 8. In addition, the output of the power supply 6 is connected to the second input of the DUT 3. The output of the PC 7 is connected to the control input of the VNA 8.

[0039] The device operates as follows.

[0040] Control commands are sent from PC output 7 to the VNA control input 8 to perform parameter measurements. The noise figure of the measured device 3 is then calculated.

[0041] Input 2 and output 4 attenuators are used to provide the necessary signal attenuation at the input and output of the device under test (3) and to ensure proper matching. Power supply 6 supplies the necessary currents and voltages for the device under test. Preamplifier 9 is designed to reduce the noise level introduced into the test setup by the vector network analyzer (8).

[0042] The main drawback of the prototype method is the need to perform a large number of reconnections (steps involving reconnections are highlighted in yellow in Fig. 1) during the test setup calibration phase, which negatively impacts the accuracy and repeatability of measurements, complicates the process, and increases the measurement time. Furthermore, there are numerous test setup configurations (not shown in Fig. 2), each of which is selected for a specific device under test (the selection is based on the DUT and VNA parameters, such as gain, noise figure, and 1 dB compression point). Furthermore, the prototype method requires the use of additional equipment, such as a power meter and an external preamplifier.

[0043] The objective is to use a single connection scheme for measuring instruments, as well as to increase the accuracy and repeatability of measurements by reducing the number of reconnections at the stage of calibration of the measuring installation.

[0044] To solve the stated problem in the method for measuring the noise figure, including the steps of measuring the losses at the input and output of the measured device, connecting the measured device to the test setup, measuring the total power and gain of the measured device, determining the noise figure of the measured device, wherein when replacing the measured device and in the event that there is no need to measure the losses at the input and output of the replaced measured device, the process of measuring the noise figure is repeated from the step of connecting the replaced measured device to the test setup, and otherwise - from the step of measuring the losses at the input and output of the replaced measured device, according to the invention, after connecting the measured device to the test setup, the noise power at the input of the measuring device of the test setup is measured and the number of averaging used is determined;the power supply of the device being measured is switched on and the noise output power of the test setup is measured; the radio frequency output of the generator is switched on with the harmonic signal level set to exceed the noise output power level of the test setup, followed by the measurement of the total noise power with the harmonic signal of the generator, and the determination of the gain of the device being measured; the signal-to-noise ratio is determined based on the results of the measurements obtained to determine the noise figure of the device being measured, taking into account the number of averagings used.

[0045] The proposed method includes the following operations, an illustration of which is shown in Fig. 3.

[0046] At the first stage “Calibration of losses at the input and output of the measuring device” (Fig. 3) (in the description, calibration should be understood as the process of measuring and recording losses at the input and output of the measuring device), the losses at the input and output of the measuring device are determined (for example, the insertion losses of high-frequency cables), which are then used until the next recalibration.

[0047] After this, the measured device is connected to the test setup (“Test setup”) without supplying power to it.

[0048] The next step is to measure the noise power of the measuring device, such as a spectrum analyzer, and determine the number of averagings to be used ("Measuring the Noise Power of the IA and Determining the Number of Averages to Be Used," Fig. 3). For this purpose, previously collected data on the dependence of the standard deviation (SD) of the measured noise signal power on the average count and sweep time for the spectrum analyzer used are used. Fig. 4 shows examples of such dependences for the R&S FSW26 spectrum analyzer. If such previously collected data are not available, the following operations are performed. The RF output on the signal generator is switched off, and multiple noise power measurements are performed to accumulate statistics. The SD is calculated from the obtained distribution of the measured noise signal power. An example of the distribution of the measured noise signal power is shown in Fig. 5.Thus, with different values ​​for the number of averages, noise power measurement statistics are accumulated, the standard deviation is calculated, and the value closest to the required error is selected. By reducing the error requirements, the measurement process can be accelerated by selecting a smaller number of averages.

[0049] The result of completing the stage “Measuring the noise power of the UI and determining the number of averagings used” is the calculation of the average value of the UI's own noise power from the obtained data sample with a certain number of averagings. From here on, all measurements are performed in the band Hz.

[0050] Then the power of the device under test is turned on (“Turning on the power of the device under test”, Fig. 3), after which the step of measuring the noise output power of the test setup is performed. using a measuring device (“Measuring the noise output power of the test setup”, Fig. 3).

[0051] In the next step “Turning on the RF output to the G with setting the signal level to exceed the required SNR” (Fig. 3), the RF output of the signal generator is turned on and the harmonic signal level is set , exceeding , for example, by 30 dB. The total noise power with the signal in the band is recorded and the gain of the measured device is calculated according to formula (1) based on And (“Measuring the total power and gain of the measuring device”, Fig. 3). The selected SNR value allows us to calculate the gain of the device being measured with minimal error, since in contains both signal and noise components, which leads to an overestimation of the gain (1). Fig. 6 shows the dependence of the difference (2) between the overestimation of the control unit of the measured device and the gain of the UI from the signal-to-noise ratio. The resulting difference At an SNR of 30 dB, it doesn't significantly contribute to the overall measurement error of the DUT's noise figure and can therefore be neglected. Moreover, the gain measurement of the device being measured is performed at a high test harmonic signal level, which eliminates unnecessary averaging and has a small spread compared to measurements at levels close to the noise level, as occurs, for example, when measuring using the Y-factor method.

[0052]

[0053]

[0054] To calculate the signal-to-noise ratio (SNR Calculation, Fig. 3) the noise power value in the band is used and the value of the noise power with the signal in the band :

[0055]

[0056] Noise figure of the measured device (“Calculation of the noise factor of the test setup”, Fig. 3) is determined by formula (7) by substituting into the Friis formula (4) the noise factor of the test setup calculated by formula (5) , KSh measuring device (6) and the gain of the measured device (1).

[0057]

[0058]

[0059]

[0060]

[0061] The calculation of the noise figure of the test setup using the cold source method (9) can be expressed from (5) by first determining (8) taking into account that :

[0062]

[0063]

[0064] In case of replacement of the measuring device (“Replacing the measuring device?”, Fig. 3) and there is no need for recalibration (“Recalibration?”, Fig. 3), the measurement process is repeated from the stage of installing the measuring device (“Installing the measuring device”, Fig. 3).

[0065] During recalibration (“Recalibration?”, Fig. 3), the measurement process is carried out from the stage of calibrating the losses at the input and output of the measured device (“Calibrating the losses at the input and output of the measured device”, Fig. 3).

[0066] The presence of an output attenuator (both external and internal) actually increases the noise floor of the measuring device. Therefore, it is necessary to determine a sufficient degree of attenuation to reduce mismatch losses and, accordingly, decrease measurement error. For this purpose, the output powers of a test setup with a spectrum analyzer as the measuring device were compared with the DUT power off (the p_out_sa curve in Fig. 7) and with the power on (the p_out_sys curve in Fig. 7) using internal and external attenuation. Internal attenuation is implemented through a measuring device option, while external attenuation is implemented by physically connecting the attenuator to the measuring device input. These measurements were correlated with the speaker output power with a 50-ohm load at the input. With an external attenuator of 5 dB at the input of the speaker system, the difference between the measured output power (curve external_p_out_sa in Fig. 7) and the output power of the speaker system with a 50 Ohm load (curve p_out_sa_range[0] in Fig.7) is 0.14 dB (loss mismatch), which can be used for automated measurements. Adding a 5 dB attenuator improves the match between the measuring equipment and the DUT, which also helps reduce the variance in the noise figure measurement of the device being measured.

[0067] The proposed method allows for measuring noise figure in a 50-ohm path and using a signal generator and an AC amplifier as the measurement device. Alternatively, the VNA transmit port can serve as the signal generator, and the MU can serve as the VNA receive port or any other measurement receiver, allowing for evaluating the energy characteristics of test and noise signals. This simplifies the test setup, making it universal for measuring noise figure and other parameters of devices with different characteristics (the connection diagram is fixed and does not change depending on the specific case).

[0068] Furthermore, the proposed noise measurement method reduces the number of reconnections by using permanently connected input and output attenuators. These attenuators can be either external separate devices or integrated into the measurement instrument. These attenuators maintain the 50-ohm output impedance of the generator and DUT in the off state, which, when measuring the noise of the measuring device, is equivalent to having a 50-ohm load at its input. This approach improves the match between the output of the device under test and the input of the measuring device in the test setup, thereby reducing the measurement error of the noise figure of the measuring device. Using a reference frequency from the device under test in the test setup ensures phase synchronization and eliminates amplitude deviations in the measured signal, as well as frequency offsets.

[0069] The technical result is the use of a single connection scheme for measuring instruments, as well as an increase in the accuracy and repeatability of measurements by reducing the number of reconnections at the stage of calibration of the measuring installation.

[0070] The proposed measurement method can be implemented by a test setup for a wide class of devices, for example, assembled according to the circuit shown in Fig. 8, where the following designations are introduced:

[0071] 1 – signal generator (G);

[0072] 2 – input attenuator (Input ATT);

[0073] 3 – measuring device (MD);

[0074] 4 – output attenuator (Output ATT);

[0075] 5 – measuring device (MD),

[0076] 6 – power supply;

[0077] 7 – personal computer.

[0078] The test setup comprises a signal generator 1, the output of which is connected via an input attenuator 2 to the first input of the device under test 3, the output of which is connected to the input of an output attenuator 4, the output of which is connected to the first input of the measuring device 5. The synchronizing inputs and outputs of generator 1 and MD 5 are interconnected. In this case, the output of PC 7 is connected to the control inputs of MD 5 and generator 1. The output of power supply 6 is connected to the second input of the device under test 3. Measuring device 5 can be, for example, a spectrum analyzer, a VNA receiving port, or any other measuring receiver that allows evaluating the energy characteristics of test and noise signals. Signal generator 1 can be the transmit port of a vector network analyzer.

[0079] The installation works as follows.

[0080] The input and output losses of DUT 3 are measured, after which the device under test (DUT) is installed between input attenuators 2 and output attenuators 4. At DUT 5, the number of averaging steps is selected for the required measurement error or speed during noise power measurement. Power is then turned on for the DUT from power supply 6, and the output noise power of the test setup is measured. When the RF output is turned on, a level is set on signal generator 1 to exceed the required signal-to-noise ratio, and the output noise power with the signal in the band, as well as the gain of DUT 3, are measured. Based on the measured data, the obtained SNR value and the noise figure of DUT 3 are calculated. The measurements described in the above method are performed under the control of commands sent from PC 7.

[0081] If DUT 3 is replaced and there is no need for recalibration, measurements are repeated from the DUT installation stage. When recalibrating, the steps are repeated starting with the input and output loss calibration of DUT 3.

[0082] Sources of information

[0083] 1. Rakhmanin, D.N. Practice of measuring the noise figure / D.N. Rakhmanin, A.V. Grechishkin, I.A. Arzamastsev, A.A. Berlev, S.V. Perova / / Collection of works of the XXXI International scientific and technical conference "Radar, navigation, communication". - Voronezh, 2025. - V. 6. - P. 207-215.

[0084] 2. Paech A., Neidhardt S., Beer M. Noise Figure Measurement without a Noise Source on a Vector Network Analyzer / / Rohde & Schwarz Application Note. – 2010. – p. 9-28.

Claims

A method for measuring the noise figure, which includes the steps of measuring the losses at the input and output of the device being measured, connecting the device being measured to a test setup, measuring the total power and gain of the device being measured, determining the noise figure of the device being measured, wherein when replacing the device being measured and in the event that there is no need to measure the losses at the input and output of the replaced device being measured, the process of measuring the noise figure is repeated from the step of connecting the replaced device being measured to the test setup, and otherwise - from the step of measuring the losses at the input and output of the replaced device being measured, characterized in that after connecting the device being measured to the test setup, the noise power at the input of the measuring device of the test setup is measured and the number of averagings used is determined; the power supply to the device being measured is turned on and the noise output power of the test setup is measured;the radio frequency output of the generator is switched on with the harmonic signal level set to exceed the noise output power level of the test setup, followed by measuring the total noise power with the harmonic signal of the generator and determining the gain of the device being measured; the signal / noise ratio is determined based on the results of the measurements obtained to determine the noise figure of the device being measured, taking into account the number of averagings used.

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