RU2353051C2 - Superconducting wide-band shf amplifier - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to cryogenic radio engineering. Superconducting wide-band SHF amplifier includes a chain of segments consisting from two-contact squids for generating periodic triangle-shaped voltage response depending on magnetic field shift value. The above segments are made up from squid groups with similar effective squares. The shift current is selected based on the condition that sinusoidal voltage response of the single squid is ensured depending on the magnetic field shift value.

EFFECT: increased level of output signal and amplification linearity factor due to multi-element Josephson structures consisting from serial connection of squids.

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Description

The invention relates to cryogenic radio engineering, in particular to amplifiers of the radio frequency range, and can be used to amplify electrical signals in the gigahertz frequency range.

Radio-frequency amplifiers based on superconducting two-contact quantum interferometers (two-contact squids) have high sensitivity and low noise temperature (T _N = 1 ... 3 K), are compatible with other superconducting devices.

There are two problems that make it difficult to switch to higher frequencies of 1-10 GHz signals while maintaining the same high gain and noise temperature, making these amplifiers competitive with semiconductor amplifiers based on transistors with high electronic mobility. Firstly, squid amplifiers are a special type of parametric amplifiers in which the signal power at its frequency F _S is amplified by converting the signal to the frequency F _S + F _J , where F _J is the frequency of the Josephson generation, and then converting it down to signal frequency. Based on the Man-Lee-Rowe ratios, the power gain, G, of such an amplifier does not exceed:

Therefore, Josephson squid transitions must have a high characteristic voltage V _C , so that the limiting frequency F _{C of} Josephson generation

(Ф ₀ - magnetic flux quantum equal to 2.07 × 10 ^-15 VB), was several orders of magnitude higher than the signal frequency F _S. For Squids based on Nb Josephson junctions, typical V _C values do not exceed 100-200 μV, respectively, F _C values do not exceed 100 GHz. Typical values of F _J at the operating point are approximately an order of magnitude smaller than F _C and, as can be seen from formula (1), the gain disappears for signals with a frequency of the order of 10 GHz. Accordingly, the noise characteristics of the amplifier are also deteriorating.

The second problem for microwave amplifiers based on classical squids in the frequency range above 0.1 GHz is the non-linear form of the voltage-voltage response to the external magnetic field. In the megahertz frequency range, these problems are solved by introducing effective compensating feedback, which is almost impossible to implement in the gigahertz frequency range.

Various designs and circuitry solutions for microwave superconductors are described. In particular, a scheme is described for a matched squid amplifier with a load for the range up to 0.1 GHz (JP 60247311, Noguchi, op. 07.12.1985). However, both the operating frequency range and the linearity of conversion for single-squid amplifiers are insufficient for modern applications.

To improve performance, it was proposed to switch to amplifiers containing a large number of interconnected squids. A serial chain of regularly located identical two-contact squids can be used as the main element for amplifying a digital or analog signal, and also as a magnetic field detector. An irregular chain of squids having arbitrary areas and orientations of interferometers is the so-called superconducting quantum interference filters (SKIFs), which can also be used in the construction of microwave amplifiers. A specific feature of SKIF follows from the irregularity of its structure: it allows one to obtain one central maximum of the voltage-field response at zero external magnetic field.

So, in the invention (DE 3936686, Hoenig, 05/08/1991) a thin-film version of an amplifier based on a squid matrix cooled by liquid nitrogen is described, however, it is indicated that it can operate up to frequencies of 100 MHz. The invention (US 6005380, Hubbell Stephen, 12/21/1999) describes an amplifier for a highly sensitive antenna using magnetically coupled squids forming a multi-element matrix. However, such a device is designed to operate in a significantly narrower frequency range and is characterized by a relatively low limit operating frequency of 516 MHz.

To create an electric signal amplifier with large output currents, it was proposed to use a set of parallel-connected DC squids (JP 2003209299, Morooka et al., July 25, 2003). However, this proposal is also not designed to operate in the GHz range.

In the invention (US 7095227 B2, Tarutani et al., 22.08.2006), an amplifier based on a sequential squid chain is described, which makes it possible to use a direct current source and occupying a small area. However, such a device allows to achieve only a relatively small linear gain of the signal, not exceeding the linear gain for a single squid.

The design of driver amplifiers based on multi-element chains of squids for the frequency range up to a dozen GHz is described, which converts BOC pulses at the input to output voltage pulses, the value of which is sufficient for further use in semiconductor electronics circuits. In the invention (US 6,486,756 B2, Tarutani et al., 11/26/2002) the chain of squid is divided into pairs isolated from the earth. This solution allows to reduce stray capacitance and increase the maximum speed of the amplifier, however, driver amplifiers are suitable only for digital applications and cannot be used to amplify an analog signal. Another example of such an amplifier for BOC logic is the invention (US 6917216 B2, Herr Quentin, 10/14/2004). The principle of its operation is based on the separation and sequence of reflections of the used BOC pulse to obtain sufficient values of the output voltage pulses. But this proposal is designed exclusively for use in digital devices.

A parallel chain of variable area squid (SKIF structure) as a highly sensitive magnetometer is described (WO 0125805, Schopohl et al., 04/12/2001; WO 2004114463, Oppenlaender J. et al., 29.12.2004). However, the microwave amplifier based on the parallel SKIF structure does not provide the necessary linear amplification of the signal and does not allow, among other things, to achieve significant values of the output signal. An insufficiently high linearity of signal amplification is also characteristic of an amplifier based on a consecutive SKIF structure.

The closest set of features to the patented amplifier is a superconducting broadband microwave amplifier containing a series chain of two-contact squids connected to input and output superconducting lines associated with means for setting the operating current and magnetic field modes (JP 10028021, TAKEDA et al., January 27, 1998 - the closest analogue).

An analysis of the prior art, including the closest analogue, shows that the low linearity of the voltage response to the magnetic component of the electromagnetic signal remains a common drawback of the designs of all amplifiers made both on low-temperature metal and on high-temperature oxide superconductors and implemented both on the basis of regular chains of squid and irregular SKIF structures.

The objective of the invention is the design of a microwave amplifier based on linear chains of direct current squid, having a high gain and high linearity of the voltage response to the magnetic component of the electromagnetic signal in the frequency band 1-10 GHz.

The solution to the problem is that the superconducting broadband microwave amplifier contains an input element for supplying a microwave signal and converting it into a magnetic flux acting on a serial chain of two-contact squids, a bias constant current source, an inductive bias magnetic field mode setting means image to each of the squids of the indicated squid chain, which is connected to the specified output element in such a way as to obtain the total voltage change on it from the specified sequential chain of squids formed from segments, each of which is configured to generate a periodic voltage response to the magnitude of the magnetic displacement field specified by the specified means of defining the magnetic displacement field.

Each of the segments consists of groups of squids with the same effective areas S _kn satisfying the condition:

S _kn = n · S _k1 ,

where S _kn is the effective area of the squids of the n-th group in the k-segment;

S _k1 is the effective area of squids in the first group of the k-segment;

k = 1, 2 ... K is the number of the segment in the chain;

n = 1, 2 ... N - group number in the segment,

the bias current of the direct current source is selected from the condition of providing a sinusoidal response of the voltage of a single squid from the magnitude of the bias magnetic field B, and the voltage response of the nth group of the kth segment from the magnitude of the bias magnetic field B satisfies the condition:

, мВ,

mV

where m is the number of squids in the nth group belonging to the kth segment; V ₀ is the amplitude of the sinusoidal response of a single squid; ω _k = 2πS _k1 / Φ ₀ ; Ф ₀ = 2.07 × 10 ^-15 Wb; ΔВ is the predetermined value of the range of variation of the bias field B, in which the gain linearity is provided, mT; A is the constant determined experimentally, mV.

The device can be characterized in that the number of segments in the chain is at least two, and also in that the number of squids in the group is 1-100, and also in that the number of squid groups in the segment is 50-100.

The device can be characterized by the fact that the periodic voltage response to the magnitude of the displacement magnetic field is set common to all segments, and the response period (B _T ) _k for the k-th segment is set in accordance with the condition (B _T ) _k = Ф ₀ / S _k1 .

The device can be characterized, in addition, by the fact that the area values S _k1 for different segments are not multiple and are selected from the condition:

Ф ₀ / 2ΔВ≥S _k1 ≥0.01 Ф ₀ / 2ΔВ.

The device can also be characterized by the fact that the specified input and output elements are made in the form of a superconducting strip transmission line, while one of the contacts of each squid of the chain is included in the gap of one of the strips of the output line.

The technical result of the invention is to increase the level of the output signal and the linearity of the law of conversion of the input magnetic signal to voltage changes at the output element through the use of multi-element Josephson structures consisting of series-connected squids, the design and characteristics of which in the chain are selected in a certain way described in the invention.

The addition of responses from the components of such a chain of squids just allows you to achieve the desired level of gain. Improving the operational characteristics of the proposed structure is achieved, inter alia, due to the fact that its response from the magnetic field is not periodic, but has one pronounced maximum at the zero field.

The invention is illustrated in the drawings, where

figure 1 presents the structural diagram of the patented amplifier;

figure 2 illustrates the principle of constructing a chain;

figure 3 shows the distribution of the number of squids with a sinusoidal response according to the values of their effective area for the formation of the resulting periodic response;

in Fig.4 - non-periodic (a) and periodic (b, c) voltage responses from the applied magnetic displacement field corresponding to the continuous and discrete distributions shown in Fig.3;

figure 5 - the principle of formation of a discrete spectrum through groups of squids with the same effective areas;

figure 6 - dependence of the linearity of the response on the number of groups in the segment;

7 shows an amplifier circuit using a superconducting strip transmission line,

in Fig.8 - the same as in Fig.7, the area where the squid included in the output line is located is enlarged.

The block diagram of the patented amplifier is shown in figure 1. The superconducting broadband microwave amplifier contains a series circuit 30 of two-contact squids 32 connected to the input 10 and output 20 elements. The input element 10 contains a circuit 11 of inductive elements 12 according to the number of squids 32 having two Josephson junctions 33. The chain 30 is connected to a direct current source 40 bias and means 50 for setting the bias magnetic field mode. The tool 50 is a direct current source 52, to which inductive elements 54 are connected, each of which is connected to a single squid 32. The offset of the operating point of the squid 32 can also be carried out using inductive elements 12, in which case the source 52 must be connected to circuit 11 inductive elements 12.

Figure 2 shows the principle of constructing the chain 30. Squids 32 containing two Josephson junctions 33 forming a chain 30 are connected in series electrically and comprise K segments 300.

Each of the segments 300 consists of N _k groups of 310 squids with the same effective areas S _kn (k = 1, 2 ... K is the number of the segment in the chain; n = 1, 2 ... N is the number of the group in the segment) satisfying the condition S _kn = n · S _k1 , where S _kn is the effective area of the squids of the nth group in the kth segment; S _k1 - effective squid area in the first group of the k-th segment. The sign "effective area of a squid" is understood as the ratio of the magnitude of the magnetic flux Ф that fell into the squid to the magnitude of the induction applied to the squid of the magnetic field B.

Each of the groups 310 consists of m squids 32. The effective areas S _{kn of the} squids 32 in the groups 310 of the kth segment 300 are multiples of the areas S _{k1 of the} squids 32 in the first group 312.

In order to ensure a sufficiently high gain linearity in the gigahertz frequency range, where standard methods for increasing gain linearity due to the use of feedback systems are not applicable, it is necessary to ensure a high accuracy of the periodic V (B) response of the amplifier from the magnetic field to biases with a single maximum at zero fields. Accordingly, the bias current of the squid 32 is selected to provide a sinusoidal voltage response with an amplitude V _{0 of a} single squid from the magnetic field B bias. Further, K segments 300, in accordance with the patented invention, must have a periodic response of the voltage of the segment from the magnetic field B bias. The periodic voltage response is set common for all segments 300, and the response period (V _T ) _k for the k-th segment is set in accordance with the condition (B _T ) _k = Ф ₀ / S _k1 , Ф ₀ = 2.07 × 10 ^-15 Wb

The recommended number K of segments 300 is of the order of ten, but it is fundamentally possible to obtain a periodic response that has many peaks, in addition to the main one, at the zero field using even one segment.

Figures 3 and 4 are graphs explaining the physical principles underlying the present invention. The squid chain is formed of segments, each of which provides the formation of a periodic voltage response to the magnitude of the bias magnetic field V (B) specified by the specified means of setting the bias magnetic field, and the linear sections of the periodic piecewise-defined function V (B) form a periodic “triangular” response presented in Fig.4 b, c.

On the abscissa axis in FIG. 3, the distribution of groups 310 is plotted over the areas S _{kn of} squids 32, and on the ordinate axis is the number m of elements in the group, which ensures the formation of a periodic voltage response of the kth segment 300 from magnetic field 6. The continuous spectrum shown in pos. 60 corresponds to response (a) in FIG. The discrete spectra of pos. 62 correspond to response (b), and the spectrum of pos. 64 corresponds to response (c).

, мВ, Figure 5 explains the principle that allows you to provide the necessary response value of group 310: the number m of squids 32 in the n-th group belonging to the k-th segment, is selected in accordance with the law "sync squared":

mV

where V ₀ is the amplitude of a single squid, A is a constant determined experimentally, mV, ω _k = 2πS _k1 / Ф ₀ .

Figure 6 presents the calculated dependence of the response linearity on the number of groups 310 in the segment 300. For a finite number of spectral components, the linearity of the presented spectra does not depend on the initial frequency of the discrete spectrum and is determined by the frequency of the last component taken. From the point of view of the number of used squids, the discrete spectrum with the initial frequency ω _k = 1 is optimal (spectrum (c) in FIG. 4).

If it is necessary to generate a non-periodic response, the number k of segments 300 should be of the order of 10 ... 30, and the area values S _k1 for different segments 300 should be selected in the range from the maximum value of Ф ₀ / 2ΔВ to the minimum value (0.01 ... 0.1) Ф ₀ / 2ΔВ and not be multiple. This will lead to the fact that the addition of responses with different periods will ensure the formation of a voltage response of the entire chain with a single maximum at zero magnetic field (B = 0).

7, 8 shows a broadband microwave amplifier on a sequential chain of 30 squid 32, operating on the principle of a traveling wave, using input 10 and output 20 elements in the form of input 70 and output 80, 81 superconducting strip lines. At the end of the input line 70 and at the beginning of the output line 80, matched loads 73 and 82 are included, respectively. Josephson junctions 33 are included in the gaps of the output strip line 81. The arrows of pos. 72 conventionally indicate the areas of local influence of the input wave on the amplifier squids, and the arrows of pos. 83 - the region of space where the amplified wave propagates.

All elements of a superconducting broadband microwave amplifier can be performed using electronic lithography and placed on a single dielectric substrate. The manufacturing technology of such structures is known and described (http://www.hypres.com), therefore, is not given in the present description.

The device operates as follows (see figure 1, 2). Upon receipt of the microwave signal at the input element 10, it is converted by means of inductive elements 12 into a magnetic flux acting on the squid 32, shifted by the current source 40 to the resistive state. This effect causes a change in the constant component of the voltage V ₀ in SQUID 32. The total change in voltage at the output element 20 of the circuit 30 is directly proportional, with a high degree of accuracy, to the magnitude of the input signal. Estimates show (see FIG. 6) that high linearity (up to 120 dB) in the range of amplification frequencies up to several tens of GHz can be achieved for a reasonable number of squids 32 in chain 30. To obtain, for example, as shown in FIG. 6, linearity of the order of 80 dB requires 25 groups of skids. Moreover, with an increase in the number of the group n (and, therefore, its effective area), the number of squids in the group, providing a response that changes with number n according to the above-mentioned “square squared” law, drops to unity in the group with number N. Thus, in In the case of using squids with the same response, in order to achieve high gain linearity, it is sufficient to produce a sequential chain of approximately 760 single squids.

For the design shown in FIG. 7, the amplifier operates in a similar manner. When a microwave signal is supplied to the input element 10, it is converted into a magnetic flux (conventionally indicated by arrows pos. 72), acting on the squid 32 of the chain, and thus the output microwave signal 20 is excited, since one of the Josephson junctions 33 of each squid 32 is included in rupture of the output superconducting strip line 81. As it propagates along the strip line to element 20, the output signal increases (conventionally shown by arrows pos. 83).

This embodiment of the microwave amplifier allows you to implement a multi-element long chain 30, the dimensions of which are comparable or exceed the wavelength, without restrictions associated with the distribution of the system.

Claims (7)

1. A superconducting broadband microwave amplifier containing an input element for supplying a microwave signal and converting it into a magnetic flux acting on a serial chain of two-contact squids, a bias current source, a bias magnetic field mode setting means, connected inductively to each of the squids the specified chain of squid, which is connected to the specified output element in such a way as to obtain on it the total voltage change from the specified sequential chain of sk ide, formed of segments, each of which is adapted to generate a periodic voltage response on the magnetic bias field, said means predetermined reference magnetic field in the displacement mode, wherein
each segment consists of groups of squids with the same effective areas S _kn satisfying the condition
S _kn = n · S _k1 ,
where S _kn is the effective squid area of the nth group in the k-segment;
S _k1 — effective squid area in the first group of k-segment squids;
k = 1, 2 ... K is the number of the segment in the chain;
n = 1, 2 ... N - group number in the segment,
the bias current of the direct current source is selected from the condition of providing a sinusoidal response of the voltage of a single squid from the magnitude of the bias magnetic field B and the voltage response of the nth group of squids of the kth segment from the magnitude of the bias magnetic field B satisfies the condition

where m is the number of squids in the p-th group belonging to the k-th segment; V ₀ is the amplitude of the sinusoidal response of a single squid; ω _k = 2ttSk ₁ / Φ ₀ ; Ф ₀ = 2.07 × 10 ^-15 Wb; ΔВ is the predetermined value of the range of variation of the magnetic field of the bias, in which the gain linearity is ensured, and A is the constant determined experimentally, mV. 2. The device according to claim 1, characterized in that the number of segments in the chain is at least two. 3. The device according to claim 1, characterized in that the number of squids in the group is 1-100. 4. The device according to claim 1, characterized in that the number of squid groups in the segment is 50-100. 5. The device according to claim 1, characterized in that the periodic voltage response to the magnitude of the bias magnetic field is set common to all segments, and the response period (B _T ) _k for the k-th segment is set in accordance with the condition (B _T ) _k = Φ ₀ / S _k1 . 6. The device according to claim 1, characterized in that the area values Sk ₁ for different segments are not multiple and are selected from the condition
Ф ₀ / 2ΔВ≥S _k1 ≥0.01 Ф ₀ / 2ΔВ. 7. The device according to claim 1, characterized in that said input and output elements are made in the form of a superconducting strip transmission line, while one of the contacts of each squid of the chain is included in the gap of one of the strips of the output line.

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