RU63604U1 - HIGH VOLTAGE BROADBAND ATTENUATOR WITH OVERLOAD PROTECTION - Google Patents

Abstract

The proposed utility model relates to pulsed technology and can be used in the signal paths of the measuring channels, at the input of oscillographic recorders (OR). Functions: reduction of the amplitude of the studied pulse signal, so that the amplitude of the signal at the output of the attenuator is in the dynamic range of the OR recording; protection of the attenuator itself and subsequent devices from pulse overloads with a pulse amplitude above a certain threshold value.

The technical result of this proposal is to expand the functionality while ensuring high parameters of the signal path: frequency response uniformity and minimum SWR. by reducing reflections and improving the frequency response of the device.

The essence of the proposed technical solution is to use the same elements to implement the functions of the attenuator and to implement the protective function. The implementation of the attenuator with overload protection in one housing has reduced the number of plug-in connections from 4 (typical for the use of autonomous units) to 2.

The technical result was achieved by a new constructive solution, namely, a protective element was introduced into the attenuator housing, the dielectric board being made with a gap, over which a metal jumper is installed, which is connected with the wave resistance of the MPL, connecting the gap of the MPL signal conductor, and a screen enveloping the jumper connected to the upper case cover with a gap excluding their electrical contact and dividing the housing into an attenuator section and a protective element section included in the MPL gap of the protective section element screen conductor formed MPL metallization other side of the dielectric board and a base body, the width of signal conductors MPL attenuator section and a section of the security element are determined from the consistency of the conditions of the characteristic impedance of each portion of the signal conductor MPL. Fig. 3 l

Description

The proposed utility model relates to pulsed technology and can be used in the signal paths of the measuring channels, at the input of oscillographic recorders (OR). Functions: reduction of the amplitude of the studied pulse signal, so that the amplitude of the signal at the output of the attenuator is in the dynamic range of the OR recording; protection of the attenuator itself and subsequent devices from pulse overloads with a pulse amplitude above a certain threshold value.

When registering pulsed processes using many methods, one-time and rarely repetitive pulsed signals with steep edges of the subnano-picosecond range of duration up to the microsecond range and amplitude up to hundreds of volts are studied. In addition, pulse paths with a duration of up to several microseconds and an amplitude of up to several kilovolts are possible in the signal path, in this case, the pulse currents during the overload reach several kiloamperes. Consequently, two blocks must be installed in the signal path - protective - arrester-fuse, which will protect the subsequent blocks and elements of the signal path from the penetration of pulses with an amplitude higher than the specified one, and an attenuator, which will attenuate the signal under investigation to an amplitude corresponding to the dynamic range of the input OR. Accordingly, the bandwidth of these blocks should extend to several GHz, since each block in the signal path degrades the bandwidth and frequency response uniformity.

Known diode power limiters of the microwave signal (1, US Pat. RF No. 2258278, 1840159, 2097878). They are intended mainly for working with periodic signals. As noted above, protective elements and voltage dividers operating in a pulsed mode are necessary.

An element that combines high parameters with respect to amplitude, to discharge current, with miniature, ease of installation in MPL and low capacity in operating mode can satisfy the requirements for the protective part. Specifically, these requirements are met by miniature gas dischargers manufactured by Epcos, Germany. (2) So for the indicated parameters an ES90X spark gap of this company can be used, having the following main parameters: impulse voltage of limitation 450 V,

a single pulsed discharge current of 10 kA with a pulse duration of up to 8 μs, a capacitance of not more than 1 pF, dimensions of F8 × 6 mm allow the ES90X arrester to be built in parallel into the MPL signal conductor.

Attenuators are known (3, Pat. RF №2003112405, 2234169, 2224338), in which the absorbing element is included at a distance multiple of the wavelength from the input, this determines the narrow frequency range of the attenuator.

Known multi-section high voltage voltage divider SDNR 7 - (catalog FSUE NIIIT www.niiit.ru, 4, according to the invention No. 1660561 - development of the applicant: FSUE NIIIT), made in microelectronic design. The complexity of the design and manufacture do not allow him to choose as a prototype.

The catalog (4, www.niiit.ru.) Also presents high-speed pulse fuses designed to protect microwave nodes from microsecond pulses in 75 and 50 ohm paths.

The proposed utility model is intended for combining in one design, (a housing with input and output RF connectors), two functions - protective and attenuator functions while ensuring frequency response uniformity in a given frequency band, minimum reflections - that is, a minimum standing wave coefficient (SWR). The requirements on the amplitude, power, and discharge current of transmitted pulses, as described above, are also preserved. The simplicity of the design and the manufacturability of the utility model justifies its use in multichannel systems

The closest technical solution to this proposal is an attenuator (5 Electronics, Science, Technology, Business No. 2, 2006, pp. 33-34.) Containing the input and output high-frequency (HF) coaxial connectors connected to the top and the end of the signal conductor of the microstrip line (MPL) located on the dielectric board located on the base of the housing, on one side of the dielectric board there is an attenuator included in the MPL gap, the other side of the dielectric board is metallized. A description of the attenuator is presented in (5), a U-shaped diagram and attenuator calculations are presented in (6). The disadvantage of the prototype is limited functionality. The introduction of an autonomous protective unit into the signal path increases the number of connections and, therefore, worsens the frequency response uniformity and causes reflections in places of heterogeneity, i.e. increases SWR.

The technical result of this proposal is to expand the functionality while ensuring high parameters of the signal path: uniformity of frequency response and minimum SWR due to the reduction of RF-detachable connections and thereby reduce the heterogeneity of the signal path.

The technical result in a high-voltage broadband attenuator containing input and output coaxial connectors connected respectively to the beginning and end of the signal strip of the microstrip line (MPL) located on the dielectric board located on the base of the housing, on one side of the dielectric board there is an attenuator included in the MPL gap , the other side of the dielectric board is metallized, achieved by the fact that the protective element is introduced, and the dielectric board is made with a gap, above which installed a metal jumper compatible with the wave resistance of the MPL, connecting the gap of the MPL signal conductor, and a screen that closes the upper cover of the case, envelopes the jumper with a gap that excludes their electrical contact and separates the case into the attenuator section and the protective element section included in the MPL gap of the protective section element, the shield conductor of the MPL is formed by metallization of the other side of the dielectric board and the base of the housing, the width of the signal conductors of the MPL of the attenuator section and sections of the protective element are determined from the condition of consistency in wave resistance in each section of the signal conductor MPL.

The essence of the proposed technical solution is to use certain elements of the attenuator to implement the protective function, by reducing the number of RF-detachable connections from 4 (typical for the use of autonomous units) to 2. The applicant’s proposal presented an option for using a gas discharge device as a protective element that meets the requirements set out above. As an attenuator, a resistive divider is used, included in a U-shaped circuit.

The design of the proposed device is presented in FIGS. 1a, 1b, in FIG. 2 a simplified characteristic of the proposed unit is presented, which reflects the algorithm of its operation, in FIG. 3 is an equivalent circuit of the proposed unit taking into account the main spurious elements, in FIG. 4 is the frequency response and SWR optimized devices.

Accepted designations on figa, b:

RF input and output connectors 1, 2, case 3, attenuator top cover 4 (is not involved in the PM formula), RF dielectric board 5, attenuator section 6, housing base 7, signal conductor 8 MPL, gas discharge section, 9, a film pass-through resistor 10 (does not participate in the formula) of a U-shaped circuit, central conductors 12, 11 of the RF connectors 1, 2, grounding discrete film resistors (do not participate in the formula) 13, 14 of a U-shaped circuit, each of which is divided into 2 parallel resistors, gas discharge 15,

a screen 16 separating the device into sections of the gas discharge and attenuator, a metal jumper 17 connecting the signal conductor 8 of the sections of the gas discharge and attenuator, the terminals of the gas discharge 18, the metallization of the other side of the dielectric board is indicated by 19. The need for the screen 16 is due to the fact that during the operation of the gas discharge 9 powerful pulsed currents up to several kA, which contribute to the occurrence of electromagnetic interference, which, in turn, can penetrate directly to the input of OR. These reasons also necessitate the implementation of a dielectric circuit with a gap.

The following materials and radioelements can be used in the device:

- in the U-shaped circuit, discrete film resistors 10, 13, 14 - series P1-12, the ratings are determined by the formulas from (6) depending on the specified division coefficient and input and output voltages;

- 1.2 RF connectors in the frequency band up to 3-5 GHz - imported connectors of the BNC series at 50 or 75 Ohms or their domestic counterparts;

- Epcos two-electrode gas discharge device - EC 90 XN series (pulse discharge voltage 450 V).

- case material 3 and cover 4 - brass, coating - tin-bismuth;

- dielectric board 5, can be made of RF foil material FAF-4.

On the installation side of the gas discharge 15 and the resistors 10, 13, 14, the signal conductor MPL 8 is located on the dielectric board, on the other hand, the dielectric board 5 is completely metallized and is adjacent to the base of the housing 7. The base of the housing 7 must have a high degree of flatness and high surface cleanliness. The shield conductor MPL is formed by metallization of the other side of the dielectric board 5 and the base 7. The metal bridge 16 is made of copper foil coated with an alloy: tin-bismuth. The screen 16 near the rupture of the dielectric board has a recess and bends around the jumper 17 with a gap eliminating the electrostatic relationship. The screen 16 may be made of the same material as the housing.

The gas discharge housing 15 is “recessed” into the base of the housing 7, i.e. is connected electrically and mechanically with it, and is included in the gap of the signal conductor 8 MPL in the gas discharge section 9. A feed-through film resistor 10 of the U-shaped attenuator circuit is included in the gap of the signal conductor 8 MPL of the attenuator section 6, grounding resistors 13, 14 of the U-shaped attenuator circuit connected respectively to one of the terminals of the passage resistor 10 and the base of the housing 7.

In the applicant's proposal, in order to reduce power dissipation, grounding resistors 13, 14 are made in the form of two resistors in parallel each.

The accepted notation in figure 2 .:

Uin - value of the input voltage before the operation of the gas discharge

Uin ₀ - device operating voltage U residual voltage after the operation of the gas discharge

Uin _max - the maximum allowable voltage of the device

N is the division coefficient of the attenuator.

Accepted notation in figure 3

1, 2 - input and output coaxial connectors;

10, 13, 14 - discrete film resistors of the U-shaped attenuator circuit;

Сn1-Сn3 - parasitic capacitance of resistors 10, 13, 14;

L1 is the parasitic inductance of the terminals of the gas discharge;

15 - gas spark gap;

Sp4 - parasitic capacity of the gas discharge;

XW1 - MPL segment in which the gas discharge is included;

XW2 - segment of the MPL in which the attenuator section is included;

XW3 - strip line segment equivalent to jumper 17.

The calculation of the sizes of the elements of the MPL attenuator is carried out according to the formulas from (6, 7).

The proposed attenuator works as follows. An input pulse signal of amplitude A in and rise time of the front T in through the RF input connector 1, the input segments of the MPL XW1, passes through a circuit with a gas discharge 15 included in the MPL segment XW 1 and triggered according to the dynamic characteristic of the device shown in figure 2. Further, the signal, passing through jumper 17, enters the resistive divider from elements 10, 13, 14, which is included in the U-shaped circuit in the MPL section XW2, which provides direct voltage division by a factor of N times. Due to the presence of spurious elements shown in Fig. 3, and especially the capacitance of the gas-discharge device Sp4 and the inductance of its terminals L1, the division coefficient at high frequencies changes, which leads, accordingly, not only to the division of the pulse signal by a factor of N up to the amplitude Avykh = Avkh / N, but also to distortion of its shape, that is, to delaying the rise time of the front T o and the appearance of an outlier at the top. The signal changed in this way can pass through the output RF connector 2 to the subsequent blocks of the measuring channel.

To compensate for the influence of these elements on the dynamic characteristics of the device, the parameters of the MPL XW1 segment (gas discharge location and width),

optimized to a minimum of reflections, which will lead to the smoothest frequency response. Compensation of spurious elements of the gas discharge in a given frequency band, in accordance with the conditions of broadband compensation (7), is carried out by choosing the width of the segments of the MPL strip XW1 and XW2 and the place where the gas discharge P1 is included in the segment XW1. Thus, according to file 4-24, p. 89 (7), the XW1 segment is calculated, then the path is optimized for minimal reflections (VSWR). Optimization is carried out on a computer by changing the length and width of XW1, XW2 and calculating for each option the resulting frequency response and VSWR. In this case, the necessary condition is the coordination of all elements of the path: connectors, jumpers 17, the coordination of which is carried out by choosing its width, and the length of the MPL, the width of which, depending on the thickness of the board and the dielectric constant of the dielectric, must be consistent with the dimensions of the elements installed in it. Control and adjustment of the shape of the frequency response and (or) the frequency response is carried out by applying to the attenuator a pulse with a front of 70-120 ps, for example, from a pulse generator G5-84, and monitoring the pulse passed through the device on a stroboscopic oscilloscope with a passband of at least 10 GHz, e.g. C1-94 / 1, C1-122 / 1.

The optimization result (AFC - Fig. 4a, and VSWR - Fig. 4b) for the values of the parasitic capacitance of the gas discharge C = 1.5 pF and the inductances of the two gas discharge inlets of 0.5 nH each are shown in Figure 4. Figure 4 shows that the frequency response is smooth without emissions (bandwidth 1.3 GHz), determined by the size and method of switching on the resistors of the U-shaped attenuator circuit and the VSWR in the frequency range up to 2 GHz does not exceed 2.5.

Thus, the proposed device has a protective function of the signal path and the function of the attenuator while ensuring uniformity of frequency response and a satisfactory value of SWR. The next advantage of the proposed device is the relative simplicity of the design, its manufacturability and, therefore, relatively low cost, which is an important factor when used in multichannel systems.

Literature

1. RF patent No. 2258278, 1840159, 2097878.

2. "Electronics", science, technology, business No. 2, 2006, pp. 40-41.

3. RF patents №2003112405, 2234169, 2224338

4. Invention No. 1660561 - development of the applicant: FSUE NIIIT

compensated attenuator SDNR7 (catalog FSUE NIIIT www.niiit.ru).

5. "Electronics", science, technology, business No. 2, 2006, pp. 33-34. - prototype

6. Edited by V.I. Volman Handbook for the calculation and design of strip devices. Owls Radio 1982, pp. 192-193

7. GV Glebovich, IP Kovalev “Broadband transmission lines of impulse signals”, M., Sov. Radio, 1972, pp. 89-96.

Claims (1)

High-voltage broadband attenuator with overload protection, containing input and output coaxial connectors connected respectively to the beginning and end of the signal strip of the microstrip line (MPL) located on the dielectric board located on the base of the housing, on one side of the dielectric board there is an attenuator included in the gap MPL, the other side of the dielectric board is metallized, characterized in that a protective element is introduced, and the dielectric board is made with a gap, above which installed a metal jumper compatible with the wave resistance of the MPL, connecting the gap of the MPL signal conductor, and a screen that closes the upper cover of the case, envelopes the jumper with a gap that excludes their electrical contact and separates the case into the attenuator section and the protective element section included in the MPL gap of the protective section element, the shield conductor of the MPL is formed by metallization of the other side of the dielectric board and the base of the housing, the width of the signal conductors of the MPL of the attenuator section and sections of the protective element are determined from the condition of consistency in wave resistance in each section of the signal conductor MPL.