JP7189910B2 - Transformer coupled amplifier circuit - Google Patents

Description

The present disclosure relates to an amplifier circuit that uses a transformer to provide current feedback and voltage feedback.

An amplifier circuit that uses transformers for current and voltage feedback has a low noise floor and wide frequency band characteristics, as will be described shortly below with reference to FIG.

A conventional transformer-coupled amplifier circuit 1 is shown in FIG. The bipolar transistor 13 has its base terminal grounded. The first winding 12, the second winding 14, and the third winding 15 are magnetically coupled in opposite phases to each other. The second winding 14 and the third winding 15 are connected in series with the same polarity. A first winding 12 is connected between the input terminal 11 and the emitter terminal of the bipolar transistor 13 . A second winding 14 is connected between the collector terminal of the bipolar transistor 13 and the node 17 just before the output terminal 16 . A third winding 15 is connected between ground or power and a node 17 just before the output terminal 16 .

The winding ratio of the first winding 12 and the third winding 15 is 1:4 in order to quadruple (12 dB) the gain of the transformer-coupled amplifier circuit 1 at the magnetic coupling coefficient k=1. , the voltage at the input terminal 11 is 1e and the voltage at the output terminal 16 is 4e. In order to equalize the input and output impedances R _IN and R _OUT of the transformer coupled amplifier circuit 1, if the current flowing in from the input terminal 11 is 1i, the current flowing out to the output terminal 16 should be 4i. Just do it.

The current through the first winding 12, from the input terminal 11 to the emitter terminal of the bipolar transistor 13, is 1i. The current through the second winding 14 is 1i from the collector terminal of the bipolar transistor 13 to the node 17 due to the nature of the bipolar transistor 13 . The current through the third winding 15 from ground or power to node 17 is 4i-1i=3i. If the winding ratio of the first winding 12, the second winding 14, and the third winding 15 is 1:n:4, then 1i×1+1i×n=3i×4 due to the nature of the transformer. The winding ratio of the first winding 12, the second winding 14 and the third winding 15 is 1:11:4. The voltage at the collector terminal of bipolar transistor 13 is (11+4)e=15e.

In order to change the gain of the transformer-coupled amplifier circuit 1 from 4 times (12 dB) to 5 times (14 dB) at the magnetic field coupling coefficient k=1, the first winding 12 and the second winding 14 and the winding ratio of the third winding 15 may be changed from 1:11:4 to 1:19:5, and the voltage at the collector terminal of the bipolar transistor 13 may be changed from 15e to 24e.

Thus, the transformer coupled amplifier circuit 1 uses a single transformer around which the first winding 12, the second winding 14 and the third winding 15 are wound to perform current feedback and voltage feedback. Therefore, the amount of negative feedback can be increased. Besides the bipolar transistor 13, there is no thermal noise source. Therefore, a low noise floor and wide frequency band characteristics can be obtained.

However, if the input/output impedances R _IN and _{R OUT} of the transformer-coupled amplifier circuit 1 are equally 50Ω, then e/i=50Ω, and the load impedance RTR viewed from the bipolar transistor 13 is If the gain is 4 times, it is 50×15/1=750 Ω, which is large. Therefore, unless the power supply voltage of the transformer-coupled amplifier circuit 1 is increased, the intercept point of the transformer-coupled amplifier circuit 1 cannot be increased.

Therefore, in order to solve the above problems, an object of the present disclosure is to obtain a low noise floor, a high intercept point, and wide frequency band characteristics in an amplifier circuit that performs current feedback and voltage feedback using a transformer.

In order to solve the above problems, the amplifier circuit shown in FIG. 2 is applied. The bipolar transistor is shown in FIG. 2, but the field effect transistor is not shown in FIG.

Specifically, the present disclosure relates to a grounded-emitter bipolar transistor or a grounded-source field effect transistor connected in series with each other in the order from the input terminal to the output terminal of the transformer coupled amplifier circuit and magnetically coupled to each other. a first winding, a second winding and a third winding, wherein the base terminal of the bipolar transistor or the gate terminal of the field effect transistor is between the first winding and the second winding. and the collector terminal of the bipolar transistor or the drain terminal of the field effect transistor is connected to the node between the second winding and the third winding. It is a combined amplifier circuit.

According to this configuration, it is possible to obtain a low noise floor, a high intercept point, and wide frequency band characteristics in an amplifier circuit that performs current feedback and voltage feedback using a transformer (specifically, see the description below. ).

Further, the present disclosure is characterized in that the first winding, the second winding, and the third winding are connected in series with the same polarity, and the first winding, the second winding, and the third winding are connected in series. is 1:n-1:1, and the gain of the transformer-coupled amplifier circuit is n times the magnetic field coupling coefficient k=1. be.

Further, the present disclosure is a transformer coupling amplifier circuit, wherein the load impedance seen from the bipolar transistor or the field effect transistor is smaller than the input/output impedance of the transformer coupling amplifier circuit.

With this configuration, the load impedance seen by the bipolar transistor (shown in FIG. 2) or the field effect transistor (not shown in FIG. 2) is smaller than the input/output impedance of the amplifier circuit. Therefore, the intercept point of the amplifier circuit can be increased without increasing the power supply voltage of the amplifier circuit.

Further, the present disclosure is a transformer coupled amplifier circuit, wherein the first winding, the second winding and the third winding are wound around a single core.

With this configuration, the amplifier circuit does not require two transformers, but only a single transformer, so that even if this transformer is not an ideal transformer, it will produce unwanted oscillations at specific frequencies. Hard to wake up. Thus, the amplifier circuit can be easy to design and manufacture.

Thus, the present disclosure can obtain a low noise floor, a high intercept point, and wide frequency band characteristics in an amplifier circuit that performs current feedback and voltage feedback using a transformer.

1 is a diagram showing a conventional transformer-coupled amplifier circuit; FIG. 1 illustrates a transformer-coupled amplifier circuit of the present disclosure; FIG. FIG. 3 illustrates a winding method for each winding of the present disclosure;

Embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of implementing the present disclosure, and the present disclosure is not limited to the following embodiments.

A transformer-coupled amplifier circuit 2 of the present disclosure is shown in FIG. The bipolar transistor 25 (or field effect transistor) has its emitter terminal (or source terminal) grounded. The first winding 22, the second winding 23, and the third winding 24 are connected in series with the same polarity in order from the input terminal 21 to the output terminal 26, and are magnetically coupled to each other. The base terminal (or gate terminal) of the bipolar transistor 25 (or field effect transistor) is connected to the node 27 between the first winding 22 and the second winding 23 . The collector terminal (or drain terminal) of bipolar transistor 25 (or field effect transistor) is connected to node 28 between second winding 23 and third winding 24 . Although FIG. 2 describes an amplifier circuit including a bipolar transistor 25, the same applies to an amplifier circuit including field effect transistors.

In the upper part of FIG. 2, the gain of the transformer-coupled amplifier circuit 2 is designed to be four times (12 dB) at the magnetic field coupling coefficient k=1. The turns ratio of line 24) is 1:4, the voltage at input terminal 21 is 1e and the voltage at output terminal 26 is -4e. The winding ratio of the first winding 22, the second winding 23 and the third winding 24 is 1:3:1, the voltage at the node 27 is 0e, and the voltage at the node 28 is - 3e.

The turns ratio of (the first winding 22 + the second winding 23) and the third winding 24 is 4:1, and the current flowing through the first winding 22 and the second winding 23 is equal to that of the bipolar transistor 25. In nature, from input terminal 21 to node 28 is 1i and the current through third winding 24 is 4i from output terminal 26 to node 28 . The voltage and current at the input terminal 21 are 1e and 1i, the voltage and current at the output terminal 26 are -4e and 4i, and the input/output impedances R _IN and R _OUT of the transformer coupling amplifier circuit 2 are equal to e /i and can be designed to have a characteristic impedance of 50Ω, for example.

The voltage drop between the collector and emitter terminals of bipolar transistor 25 is 3e. Due to the nature of the bipolar transistor 25, the current flowing between the collector terminal and the emitter terminal of the bipolar transistor 25 is 1i+4i=5i. The load impedance R _TR viewed from the bipolar transistor 25 is 50×3/5=30Ω, which is smaller than the input/output impedances R _IN and R _OUT of the transformer coupling amplifier circuit 2 and can be made smaller than in FIG. .

In the lower part of FIG. 2, the gain of the transformer-coupled amplifier circuit 2 is changed to n times at the magnetic coupling coefficient k=1, so that the first winding 22 and (the second winding 23 + the third winding 24) has a turns ratio of 1:n, the voltage at the input terminal 21 is 1e, and the voltage at the output terminal 26 is -ne. The turns ratio of the first winding 22, the second winding 23 and the third winding 24 is 1:n-1:1, the voltage at the node 27 is 0e, and the voltage at the node 28 is , −(n−1)e.

The turns ratio of (the first winding 22 + the second winding 23) and the third winding 24 is n:1, and the current flowing through the first winding 22 and the second winding 23 is equal to that of the bipolar transistor 25. In nature, from input terminal 21 to node 28 is 1i and the current through third winding 24 is ni from output terminal 26 to node 28 . The voltage and current at the input terminal 21 are 1e and 1i, the voltage and current at the output terminal 26 are -ne and ni, and the input/output impedances R _IN and R _OUT of the transformer coupling amplifier circuit 2 are equal to e /i and can be designed to have a characteristic impedance of 50Ω, for example.

The voltage drop between the collector and emitter terminals of bipolar transistor 25 is (n-1)e. Due to the nature of the bipolar transistor 25, the current flowing between the collector terminal and the emitter terminal of the bipolar transistor 25 is 1i+ni=(n+1)i. The load impedance R _TR viewed from the bipolar transistor 25 is 50×(n−1)/(n+1)Ω, and can be made smaller than the input/output impedances R _IN and R _OUT of the transformer coupling amplifier circuit 2 .

As described above, the transformer-coupled amplifier circuit 2 performs current feedback and voltage feedback using a single transformer around which the first winding 22, the second winding 23 and the third winding 24 are wound. The amount of negative feedback can be increased. Besides the bipolar transistor 25, there is no thermal noise source. Therefore, a low noise floor and wide frequency band characteristics can be obtained.

The load impedance RTR seen from the bipolar transistor 25 is _30Ω (in the case of the upper stage of FIG. 2), which is small. Therefore, the intercept point of the transformer-coupled amplifier circuit 2 can be increased without increasing the power supply voltage of the transformer-coupled amplifier circuit 2 .

The method of winding each winding of the present disclosure is shown in FIG. The first winding 22 , the second winding 23 and the third winding 24 are wound on a single core 29 . In FIG. 3, the case where a spectacle core is applied as the core 29 will be described, but the case where other cores are applied as the core 29 is the same.

In the lower left column of FIG. 3, the input terminal 21 is drawn out of the core 29, and the coaxial line or twisted line or the like is wound around the core 29 by 1 m times (1 is the winding ratio. m is an arbitrary natural number), A first winding 22 is configured. A node 27 such as a tap is formed on the coaxial line or twisted line, and the node 27 and the base terminal of the bipolar transistor 25 are connected.

In the upper right column of FIG. 3, starting from the node 27, a coaxial line or a twisted wire or the like is wound around the core 29 3m times or (n−1)m times (3 or n−1 is the winding ratio. m is the winding ratio. Any natural number.) to constitute the second winding 23 . A node 28 such as a tap is formed on the coaxial line or twisted line, and the node 28 and the collector terminal of the bipolar transistor 25 are connected.

In the lower right column of FIG. 3, starting from the node 28, the coaxial line, twisted wire, or the like is again wound around the core 29 by 1m times (1 is the winding ratio. m is an arbitrary natural number), and the third coil is wound. A winding 24 is constructed. Then, the output terminal 26 is pulled out of the core 29, and the winding of each winding is completed.

As described above, since the transformer-coupled amplifier circuit 2 requires only a single transformer, even if this transformer is not an ideal transformer, unwanted oscillation is unlikely to occur at a specific frequency. Therefore, the transformer coupled amplifier circuit 2 can be easily designed and manufactured.

In this embodiment, it is assumed that h _FE of the bipolar transistor 25 is infinite. , the gain of the transformer-coupled amplifier circuit 2 is n times. In the actual case, the h _FE of the bipolar transistor 25 cannot be assumed to be infinite, and the turns ratio of the first winding 22, the second winding 23 and the third winding 24 is 1:n-1:1. Even when the gain of the transformer coupled amplifier circuit 2 is less than n times. In an actual case, in order to increase the gain of the transformer coupled amplifier circuit 2 by n times, the winding ratio of the first winding 22, the second winding 23 and the third winding 24 should be 1:n'(> n−1):1 is desirable.

The lower limit frequency of the transformer coupled amplifier circuit 2 is determined by the L value of the transformer, and the L value of the transformer is determined by the μ value, cross-sectional area and number of turns of the transformer. In order to extend the lower limit frequency of the transformer-coupled amplifier circuit 2 to the low frequency side, for example, it is desirable to increase the μ value (relative magnetic permeability of the core) of the transformer, and the number of turns of the transformer (the above natural number m) should be increased. is desirable.

In FIG. 2, a DC cut circuit and a damping circuit may be added as required. In FIG. 3, in order to prevent unwanted oscillation at a specific frequency, the first winding 22, the second winding 23 and the third winding 24 should not have line-to-line capacitors. Winding 22 , second winding 23 and third winding 24 are preferably wound on a single core 29 .

The transformer-coupled amplifier circuit of the present disclosure can be applied to a low-noise amplifier with a low noise floor, a low-distortion high-power linear amplifier with a high intercept point, a cascade amplifier with easy impedance matching, a TV antenna booster amplifier, and the like. , wireless devices, communication devices, and the like.

1, 2: transformer-coupled amplifier circuit, 11: input terminal, 12: first winding, 13: bipolar transistor, 14: second winding, 15: third winding, 16: output terminal, 17: node. , 21: input terminal, 22: first winding, 23: second winding, 24: third winding, 25: bipolar transistor, 26: output terminal, 27: node, 28: node, 29: core

Claims (4)

an emitter-grounded bipolar transistor or a source-grounded field effect transistor;
a first winding, a second winding, and a third winding that are connected in series in the order from the input terminal to the output terminal of the transformer coupled amplifier circuit and magnetically coupled to each other;
a base terminal of the bipolar transistor or a gate terminal of the field effect transistor is connected to a node between the first winding and the second winding;
A transformer coupled amplifier circuit, wherein a collector terminal of the bipolar transistor or a drain terminal of the field effect transistor is connected to a node between the second winding and the third winding. the first winding, the second winding, and the third winding are connected in series with the same polarity,
a winding ratio of the first winding, the second winding and the third winding is 1:n-1:1;
2. The transformer-coupled amplifier circuit according to claim 1, wherein the gain of the transformer-coupled amplifier circuit is n times the magnetic field coupling coefficient k=1. 3. The transformer coupling amplifier circuit according to claim 1, wherein a load impedance seen from said bipolar transistor or said field effect transistor is smaller than an input/output impedance of said transformer coupling amplifier circuit. 4. The transformer-coupled amplifier circuit according to claim 1, wherein said first winding, said second winding and said third winding are wound on a single core. .

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