JP5797154B2 - Distributed amplifier - Google Patents

Description

  The present invention relates to a high-power and high-frequency distributed amplifier, and more particularly to a distributed amplifier for obtaining high gain, high power, high efficiency, and wideband characteristics.

Conventionally, as a distributed amplifier composed of a plurality of transistor cells, for example, there is one shown in Non-Patent Document 1.
In such a conventional distributed amplifier, regarding each transmission line connecting the output terminals of the transistors, the transmission lines and the output capacitance of the transistors are combined and regarded as pseudo transmission lines. The characteristic impedance of each pseudo transmission line is given by the real part of the gate width of the transistor cell and the optimum load impedance. Therefore, the line length of each transmission line is uniquely determined by the characteristic impedance of each pseudo transmission line and the output capacity of the transistor cell.

C. Campbell, C. Lee; V. Williams, M. Kao; H. Tserng, and P. Saunier, “A Wideband Power Amplifier MMIC Utilizing GaN on SiC HEMT Technology,” 30th IEEE Compound Semiconductor IC Symposium, I.1, October, 2008.

  However, the prior art has the following problems. That is, in the conventional distributed amplifier, as described above, the pseudo transmission line is configured based on the inductance component of the transmission line and the output capacity of the transistor cell. However, the pseudo transmission line is not an ideal transmission line and thus is narrow. It is a band. Specifically, since the pseudo transmission line is a low-pass filter itself composed of a series inductance and a parallel capacitance, the cutoff frequency of the distributed amplifier is limited by the output pseudo transmission line, which hinders broadbandization. It was.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a distributed amplifier capable of widening the bandwidth.

In the distributed amplifier according to the present invention, in a distributed amplifier composed of n (n is a natural number of 3 or more) transistor cells, when the transistor cell closest to the input terminal of the amplifier is the first, from the input terminal The length of the output transmission line connecting all the 2mth (m is a natural number of 1 or more) and (2m + 1) th transistor cells up to the output terminal is composed of the inductance component of the output transmission line and the output capacitance of the transistor cell. as the cutoff frequency of the pseudo transmission line extending in the high range that is obtained by reducing the inductance component short comb than the length of the output transmission line connecting the (2m-1) th and 2m th transistor cells.

  In the distributed amplifier according to the present invention, the length of the output transmission line connecting the 2m-th and (2m + 1) -th transistor cells is determined from the length of the output transmission line connecting the (2m-1) -th and 2m-th transistor cells. Therefore, the bandwidth of the distributed amplifier can be increased.

1 is a configuration diagram illustrating a distributed amplifier according to a first embodiment of the present invention. FIG. It is a block diagram which shows the circuit which simplified the distributed amplifier by Embodiment 1 of this invention. It is a block diagram which shows the circuit which further simplified the distributed amplifier by Embodiment 1 of this invention. It is a block diagram at the time of replacing the pseudo transmission line of FIG. It is explanatory drawing which shows the value of the inductance component of a conventional circuit. It is explanatory drawing which shows the actual impedance which anticipated the pseudo | simulation transmission line 4a side from the transistor cell output terminal 5a of the distributed amplifier by Embodiment 1 of this invention. It is explanatory drawing which shows the actual impedance which anticipated the pseudo transmission line 4b side from the transistor cell output terminal 5b of the distributed amplifier by Embodiment 1 of this invention. It is explanatory drawing which shows the change of the cutoff frequency at the time of changing the inductance component 7b of the distributed amplifier by Embodiment 1 of this invention. It is explanatory drawing which shows the calculation result of the distributed amplifier by Embodiment 1 of this invention, and the calculation result of the conventional distributed amplifier. It is a block diagram which shows the distributed amplifier by Embodiment 2 of this invention. It is explanatory drawing which shows the calculation result of the distributed amplifier by Embodiment 2 of this invention, and the calculation result of the conventional distributed amplifier.

Embodiment 1 FIG.
1 is a block diagram showing a distributed amplifier according to Embodiment 1 of the present invention.
The distributed amplifier shown in FIG. 1 includes a plurality of transistor cells 1, output transmission lines 2a, 2b, 2c,..., 2h for connecting the output sides of these transistor cells 1, and the input sides of these transistor cells 1. And an input transmission line 3 for connecting the two.

  In the illustrated distributed amplifier, when the transistor cell 1 closest to the input terminal (RFin) is the first, the output transmission line 2b connecting the 2m-th (m is a natural number of 1 or more) and the (2m + 1) -th transistor cell. , 2d, 2f, and 2h are set to be shorter than the lengths of the output transmission lines 2a, 2c, 2e, and 2h connecting the (2m-1) th and 2mth transistor cells 1. That is, when the transmission line length connecting the 2m-th and (2m + 1) -th transistor cells 1 is defined as α, and the transmission line length connecting the (2m−1) -th and 2m-th transistor cells 1 is defined as β, the input terminal The relationship between α and β from RFin to output terminal RFout is always such that α <β.

  As an index for determining the performance of the distributed amplifier, there is a method of looking at an impedance mismatch at the output terminal of the transistor cell 1. Of this mismatch, the actual part is described in existing literature (for example, see Non-Patent Document 1). Although already described, since it is necessary in the following description, it will be briefly described here again.

  Among distributed amplifiers, in particular, non-uniform amplifiers are designed so that the optimum load impedance of each transistor cell is given to all transistor cells. At first, paying attention only to the real part of the optimum load impedance, the characteristic impedance of the pseudo transmission line composed of the transistor cell and the output line is determined. Here, Kirchhoff's current law is used, and the circuit of FIG. 1 is simplified to the circuit of FIG. 2 in order to simplify the explanation. In FIG. 2, 1 'is the optimum load resistance of the transistor cell 1, 4a, 4b,..., 4h are output pseudo transmission lines, 5a, 5b,. If the characteristic impedance of a transmission line is equal to the load resistance connected at both ends, the behavior of the transmission line can be ignored. Therefore, the configuration of FIG. 2 can be further simplified to the configuration of FIG. The non-uniform distribution type amplifier achieves wideband matching by satisfying the Kirchhoff current side at the transistor cell output terminals 5a, 5b,..., 5g of FIG.

  Next, the pseudo transmission lines 4a, 4b, ..., 4h are designed. The characteristic impedance of the pseudo transmission line is given so as to satisfy Kirchhoff's current side even if a pseudo transmission line is added to FIG. For example, the characteristic impedance of the pseudo transmission line 4a is equal to the impedance of the left branch line from the transistor cell output terminal 5a in FIG. 3, and the pseudo transmission line 4b is from the transistor cell output terminal 5b in FIG. The characteristic impedance is equal to the impedance that anticipates the branch line. After the characteristic impedances of the pseudo transmission lines 4a, 4b,..., 4h are determined in this way, the pseudo transmission lines 4a, 4b,. A characteristic impedance of 4b,..., 4h is given. Generally, the output capacitance of the transistor 1 is fixed and the inductance components of the pseudo transmission lines 4a, 4b,..., 4h are changed for each pseudo transmission line, so that the desired values for the pseudo transmission lines 4a, 4b,. Gives characteristic impedance.

  In the distributed amplifier, the most serious problem is the cutoff frequency of the pseudo transmission line. Here, the gate widths of the transistor cells 1 are all equal, and the output capacitance is Ca. Then, the pseudo transmission lines 4a, 4b,..., 4h in FIG. 2 can be replaced as shown in FIG. In FIG. 4, 6a, 6a ', 6b, 6b', ..., 6g, 6g 'are output capacities of the transistor cells, and 7a, 7b, ..., 7h are inductance components of the pseudo transmission lines 4a to 4h. FIG. 4 shows that the pseudo transmission line is a π-type low-pass filter (LPF). The cut-off frequency of this LPF is the cut-off frequency of the pseudo transmission lines 4a, 4b,.

  The LPF is a reflection type filter, and a function as a filter is realized by reflecting a high frequency without power entering the filter. That is, the cut-off frequency of the pseudo transmission line is extended to a high frequency range by reducing the amount of reflection of the filter in a desired high frequency range by some operation. That is, the frequency of the nonuniformly distributed amplifier can be increased.

  The operation of the conventional circuit and the circuit of the present invention will be described assuming the characteristics of the transistor cell. The gate widths of the transistor cells are all equal, the output capacitance Ca of each transistor cell is 0.2 pF, and the optimum load resistance Ropt of the transistor cell is 250Ω. FIG. 5 shows inductance components 7a, 7b,..., 7h of the pseudo transmission lines 4a to 4h in the conventional circuit in this case.

  First, attention is paid to the frequency characteristics of the impedance when the pseudo transmission line 4a side is expected from the transistor cell output terminal 5a of FIG. The impedance of the pseudo cell line 4a from the transistor cell output terminal 5a is ideally 250Ω with no frequency characteristics. On the other hand, the actual impedance is calculated as shown in FIG. The Smith chart is normalized by 250Ω. At a high frequency, the impedance deviates from 250Ω, and the cutoff frequency is about 4.1 GHz. Next, attention will be paid to the frequency characteristics of the impedance in anticipation of the pseudo transmission line 4b side from the transistor cell output terminal 5b of FIG. 2 in the case of the conventional circuit, that is, when the inductance component 7b is given as calculated.

  The impedance of the pseudo cell line 4b from the transistor cell output terminal 5b is ideally 125Ω with no frequency characteristics. On the other hand, the actual impedance is calculated as shown in FIG. The Smith chart is normalized at 125Ω. Similar to the transistor cell output terminal 5a, the impedance deviates from 125Ω at a high frequency, but the frequency characteristics cancel each other and the cut-off frequency extends to 10.4 GHz. In the circuit of the present invention, the inductance component 7b is reduced in order to cancel the frequency characteristic and realize a wide band characteristic. FIG. 8 shows a change in cutoff frequency from the transistor cell output terminal 5b to the pseudo transmission line 4b when the inductance component 7b is changed from 1.5 times to 0.3 times.

FIG. 8 shows that the cut-off frequency is improved when the inductance component 7b is reduced, the cut-off frequency is deteriorated when the inductance component 7b is increased, and the cut-off frequency is deteriorated when it is too small.
In this way, the frequency characteristic generated by the inductance component 7a is canceled by the inductance component 7b, and the frequency characteristic generated by the inductance component 7c is canceled by the inductance component 7d. The cut-off frequency is improved as compared with the conventional distributed amplifier. FIG. 9 shows the amount of passage through the output circuit of the conventional distributed amplifier (indicated by B in the figure) and the inductance components 7b, 7d, 7f, and 7h of the conventional circuit are increased by a factor of 0.8. The amount of passage (indicated by A in the figure) of the output circuit of the distributed amplifier of the form is shown. From FIG. 9, the circuit of the present embodiment clearly has a higher cutoff frequency, and the present invention is effective.

  Next, the length of the transmission line connecting the 2mth and (2m + 1) th transistor cells 1 is not only shorter than the length of the transmission line connecting the (2m-1) th and 2mth transistor cells 1. Further, a case where the length is shorter than the length of the transmission line connecting the (2m + 1) th and (2m + 2) th transistor cells 1 will be described.

  In the above example, when the length of the transmission line connecting the 2m-th and (2m + 1) -th transistor cells 1 is shorter than the length of the transmission line connecting the (2m-1) -th and 2m-th transistor cells 1 By repeating the frequency characteristics generated by the inductance component 7a with the inductance component 7b, and further canceling the frequency characteristics generated by the inductance component 7c with the inductance component 7d, the distributed amplifier of this embodiment is a conventional distributed type. The cut-off frequency was improved compared to the amplifier. Further, when the length of the output transmission line connecting the (2m + 1) th and (2m + 2) th transistor cells 1 is shorter, the frequency characteristic generated by the inductance component 7a is canceled by the inductance component 7b and generated by the inductance component 7c. The frequency characteristic is canceled by the inductance component 7b and the inductance component 7d, the frequency characteristic generated by the inductance component 7e is canceled by the inductance component 7d and the inductance component 7f, and so on. This is a form in which the frequency characteristic generated in one line is compensated by two lines, so that the distributed amplifier of the present embodiment can improve the cut-off frequency as compared with the conventional distributed amplifier.

  As described above, the distributed amplifier according to the first embodiment can increase the cutoff frequency as compared with the conventional one. Further, when the cut-off frequency equivalent to that of the conventional distributed amplifier is sufficient, the transistor output capacity can be increased, so that the gate width of the transistor can be increased, and the distributed amplifier can be increased in output. Further, since the cut-off frequency is increased, the operation gain at a high frequency is increased. Furthermore, in a system where a wideband amplifier is generally required, when the amplifier bandwidth is insufficient, a plurality of amplifiers having different operation bands are used to cope with the required bandwidth of the system. This widens the operating band and reduces the number of amplifiers required for the system.

  In the above example, a distributed amplifier having the same gate width of each transistor cell 1 has been described as an example. However, the same effect can be obtained even with a distributed amplifier having a different gate width of each transistor cell 1. .

  As described above, according to the distributed amplifier of the first embodiment, in the distributed amplifier composed of n (n is a natural number of 3 or more) transistor cells, the transistor cell closest to the input terminal of the amplifier is selected. When the first is set, the length of the output transmission line connecting the 2m-th (m is a natural number of 1 or more) and the (2m + 1) -th transistor cell is connected to the (2m-1) -th and 2m-th transistor cells. Since it is shorter than the length of the output transmission line, a wide band can be achieved as a distributed amplifier.

  Further, according to the distributed amplifier of the first embodiment, in the distributed amplifier composed of n (n is a natural number of 4 or more) transistor cells, the transistor cell closest to the input terminal of the amplifier is the first. When the length of the output transmission line connecting the 2m-th (m is a natural number equal to or greater than 1) and the (2m + 1) -th transistor cell, the output transmission line connecting the (2m-1) -th and 2m-th transistor cells Since it is shorter than the length and shorter than the length of the output transmission line connecting the (2m + 1) -th and (2m + 2) -th transistor cells, the bandwidth of the distributed amplifier can be increased.

Embodiment 2. FIG.
FIG. 10 is a configuration diagram illustrating the distributed amplifier according to the second embodiment.
In the distributed amplifier of the second embodiment, when the transistor cell 1 closest to the input terminal RFin of the amplifier is the first, the (3m−1) th (m is a natural number of 1 or more) and the 3mth transistor cell 1 .., 8h and the lengths of the output transmission lines 8a, 8b, 8c,..., 8h connecting the 3m-th and (3m + 1) -th transistor cells 1 (3m− 2) It is set to be shorter than the length of the output transmission lines 8a, 8b, 8c,..., 8h connecting the (3m-1) th transistor cell 1. The input transmission line 3 is the same as that in the first embodiment.

  In the first embodiment, for the length of the output transmission line connecting the 2m-th (m is a natural number of 1 or more) and the (2m + 1) -th transistor cell 1, the (2m-1) -th and 2m-th transistor cells 1 are connected. The impedance mismatch occurring in the output transmission line connecting the (2m-1) th and 2mth transistor cells 1 is made shorter than the length of the output transmission line to be connected to the 2mth and (2m + 1) th transistor cells 1. The cut-off frequency was increased by compensating for the connected output transmission line. In the second embodiment, unlike the first embodiment, the mismatch amount generated in the output transmission line connecting the (3m-2) th and (3m-1) th transistor cells 1 is expressed as (3m-1). Compensation is performed by changing the lengths of the output transmission line connecting the 3rd and 3m-th transistor cells 1 and the output transmission line connecting the 3m-th and (3m + 1) -th transistor cells 1.

  FIG. 11 shows the amount of passage through the output circuit of the conventional distributed amplifier (indicated by B in the figure) and the inductance components 7b, 7c, 7e, 7f, and 7h (see FIG. 4) with respect to the conventional circuit. The amount of passage through the output circuit of the distributed amplifier of this embodiment, which is 0.8 times (indicated by A in the figure), is shown. As shown in FIG. 11, the circuit of this embodiment clearly has a higher cutoff frequency, and it can be seen that the distributed amplifier of this embodiment is effective.

  Thus, in the distributed amplifier according to the second embodiment, the cut-off frequency can be increased as compared with the conventional one. Further, when the cut-off frequency equivalent to that of the conventional distributed amplifier is sufficient, the transistor output capacity can be increased, so that the gate width of the transistor can be increased, and the distributed amplifier can be increased in output. Further, since the cut-off frequency is increased, the operation gain at a high frequency is increased. In general, in a system where a broadband amplifier is required, when the amplifier bandwidth is insufficient, a plurality of amplifiers having different operation bands are used to cope with the required bandwidth of the system. Therefore, the operating band is widened and the number of amplifiers necessary for the system can be reduced. In FIG. 10, a distributed amplifier having the same gate width of each transistor cell 1 has been described as an example. However, the same effect can be obtained even with a distributed amplifier having a different gate width of each transistor cell 1. .

  As described above, according to the distributed amplifier of the second embodiment, in the distributed amplifier composed of n (n is a natural number of 4 or more) transistor cells, the transistor cell closest to the input terminal of the amplifier is selected. An output transmission line connecting the (3m-1) th (m is a natural number greater than or equal to 1) and the 3mth transistor cell, and an output transmission line connecting the 3mth and (3m + 1) th transistor cells. Is shorter than the length of the output transmission line connecting the (3m-2) th and (3m-1) th transistor cells, so that the bandwidth of the distributed amplifier can be increased.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  1 transistor cell, 1 'optimum load resistance, 2a, 2b, 2c, ..., 2h, 8a, 8b, 8c, ..., 8h output transmission line, 3 input transmission line, 4a, 4b, ..., 4h pseudo transmission line, 5a , 5b, ..., 5g Transistor cell output terminals, 6a, 6a ', 6b, 6b', ..., 6g, 6g 'Output capacitance of the transistor cells, 7a, 7b, ..., 7h Inductance components.

Claims (3)

In a distributed amplifier composed of n transistor cells (n is a natural number of 3 or more),
When the transistor cell closest to the input terminal of the amplifier is first, the output transmission line connecting all the 2m-th (m is a natural number of 1 or more) and (2m + 1) -th transistor cells from the input terminal to the output terminal. (2m−1) th and 2mth transistor cells so that the cut-off frequency of the pseudo transmission line composed of the inductance component of the output transmission line and the output capacitance of the transistor cell extends to a high frequency. short comb than the length of the output transmission line connecting the in distribution type amplifier, characterized in that reduced the inductance component. In a distributed amplifier composed of n transistor cells (n is a natural number of 4 or more),
When the transistor cell closest to the input terminal of the amplifier is first, the output transmission line connecting all the 2m-th (m is a natural number of 1 or more) and (2m + 1) -th transistor cells from the input terminal to the output terminal. (2m−1) th and 2mth transistor cells so that the cut-off frequency of the pseudo transmission line composed of the inductance component of the output transmission line and the output capacitance of the transistor cell extends to a high frequency. shorter than the length of the output transmission line connecting the and is characterized in that a reduced (2m + 1) th and (2m + 2) -th inductance component short comb than the length of the output transmission line connecting the transistor cells Distributed amplifier. In a distributed amplifier composed of n transistor cells (n is a natural number of 4 or more),
When the transistor cell closest to the input terminal of the amplifier is the first, the output connecting all the (3m-1) th (m is a natural number of 1 or more) and 3mth transistor cells from the input terminal to the output terminal. The length of the output transmission line that connects the transmission line and the 3m-th and (3m + 1) -th transistor cells, from the length of the output transmission line that connects the (3m-2) -th and (3m-1) -th transistor cells A distributed amplifier characterized by a short length.

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