JP2007306530A - Active coil antenna and receiver using the active coil antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To principally provide a means for downsizing a high sensitivity coil antenna for a mobile receiver such as a radio wrist watch. <P>SOLUTION: An amplifier is combined with a coil antenna to set a gain of the amplifier to a desired value so as to increase the inductance of the coil antenna, thereby realizing a high sensitivity active coil antenna. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a means for realizing an active coil antenna that is small in size, high in sensitivity, and variable in use frequency by combining an amplifier having a gain of less than +1 and a coil antenna.

  The coil according to the present invention includes a bar-type coil and a loop-type coil. In general, a bar-type coil is a coil in which a coil is wound around a rod-shaped magnetic body and the number of turns is increased by reducing the diameter of the coil. A loop-type coil is wound in a loop around an insulator, and the diameter of the coil It is the one that increases the number of turns and reduces the number of turns of the coil. However, there is no essential difference electrically.

  Broadcast frequencies including audio broadcasts and professional broadcasts are 30 kHz to 300 KHz in the LF band, and 40 kHz and 60 KHz are broadcast frequencies for radio clocks in the United States, 60 KHz in the United States and the United Kingdom overseas, and 77.5 KHz in Germany. There is a long wave broadcast of 150 KHz to 280 KHz. In addition, there are AM broadcasts in the MF band of 300 KHz to 3 MHz, short wave broadcasts in the HF band of 3 MHz to 30 MHz, and FM broadcasts in the VHF band of 30 MHz to 300 MHz.

  The bar-type coil antenna is mainly used for broadcasting frequencies in the LF band and the MF band, and the loop-type coil antenna is mainly used for broadcasting frequencies in the HF band.

  In general, there is no problem because the size of the capacitor does not increase so much even if the capacitance is increased, but the coil has a fate that the size increases in proportion to its inductance. For this reason, there were many problems in product design.

  Conventionally, when realizing an antenna composed of a bar-type coil and a capacitor, the coil has been reduced in size by selecting a bar-type magnetic body having as high a permeability as possible. In order to increase the magnetic permeability of the magnetic material, it is possible to make the shape of a closed magnetic circuit, but because of the closed magnetic circuit, it is not suitable as an antenna that is an interface circuit with a free space electromagnetic field.

  Therefore, there is a limit in obtaining a large magnetic permeability in the bar-type magnetic body, and thus there is a limit in downsizing the bar-type coil.

  Even in the case of a loop type coil antenna, in order to obtain a required inductance, the diameter of the coil may be too large or the number of turns may be increased.

  The problem to be solved by the present invention is to provide means for fundamentally improving these problems of the bar-type and loop-type coil antennas, which are composed of conventional coils and capacitors.

  As described above, since the bar-type coil and the loop-type coil are not electrically different, they will be collectively referred to as a coil antenna in the following.

  According to the first aspect of the present invention, in the coil antenna composed of a coil and a capacitor, the inductance is expanded by combining an amplifier and a coil having a gain of less than +1. The present invention provides means for realizing an active coil antenna capable of resonating. The capacitor includes the grounding capacity of the coil.

  The invention according to claim 2 provides means for varying the antenna resonance frequency by changing the gain of the amplifier within a range of less than +1 in the active coil antenna according to the invention of claim 1.

  The invention described in claim 3 provides means for varying the antenna resonance frequency by changing the capacitance of the capacitor in the active coil antenna according to the invention described in claim 1.

  The invention described in claim 4 provides means for realizing a broadcast receiver such as a radio clock using the active coil antenna according to the invention described in claim 1, 2 or 3.

  FIG. 1 is a diagram showing a conventional bar-type coil antenna composed of a bar-type coil and a capacitor, wherein 1 is a coil having an inductance L, 2 is a capacitor having a capacitance C, 3 is a loss resistance having a resistance value R, Reference numeral 4 denotes an amplifier having a gain G of less than +1.

  FIG. 2 is a diagram showing a conventional loop-type coil antenna including a loop-type coil and a capacitor. 1 is a coil having an inductance L, 2 is a capacitor having a capacitance C, 3 is a loss resistance having a resistance value R, Reference numeral 4 denotes an amplifier having a gain G of less than +1.

  FIG. 3 is an equivalent circuit diagram of a conventional coil antenna. 1 is a coil having an inductance L, 2 is a capacitor having a capacitance C, 3 is a loss resistor having a resistance value R, and 4 is an amplifier having a gain G of less than +1. Reference numeral 5 denotes a current source whose current value induced in the coil is i.

  In order to use a conventional coil antenna for a low-frequency receiver such as a long wave broadcast, because the use frequency is low, it must be realized by increasing the number of turns of the coil as much as possible. The antenna had to be large. To lower the resonance frequency, it is possible to increase the capacitance of the capacitor, but at the same time the sensitivity as an antenna deteriorates, and at the same time, the bandwidth near the resonance frequency becomes extremely narrow and weak against frequency fluctuations. .

  The present invention provides means for fundamentally solving the above-mentioned incompatible problems while reducing the size of the antenna coil.

  FIG. 4 is a view showing a bar-type coil antenna comprising a bar-type coil and a capacitor according to the first aspect of the present invention, wherein 1 is a coil having an inductance of (1-G) · L, and 2 is a capacitor having a capacitance of C. 3 is a loss resistor having a resistance value R, and 4 is an amplifier having a gain G of less than +1.

  FIG. 5 is a diagram showing a loop type coil antenna comprising a loop type coil and a capacitor according to the first aspect of the present invention, wherein 1 is a coil having an inductance of (1-G) · L, and 2 is a capacitor having a capacitance of C. 3 is a loss resistor having a resistance value R, and 4 is an amplifier having a gain G of less than +1.

  FIG. 6 is an equivalent circuit diagram of the coil antenna according to the first aspect of the invention. 1 is a coil having an inductance of (1-G) · L, 2 is a capacitor having a capacitance of C, and 3 is a loss resistance having a resistance value of R. Reference numeral 4 denotes an amplifier having a gain G of less than +1, and reference numeral 5 denotes a current source having a current value i induced in the coil.

  The active coil antenna according to the first aspect of the present invention will be described with reference to the drawings and mathematical formulas, although the coil is extremely small, the equivalent circuit is exactly the same as the conventional passive coil antenna.

である。従って、共振回路に発生する電圧は、

となる。式２に式１を代入すると、

となる。これは図８に示す回路と等価である。FIG. 7 is a diagram for explaining a conventional coil antenna. 1 is a coil having an inductance L, 2 is a capacitor having a capacitance C, 3 is a loss resistor having a resistance value R, 4 is a voltage source induced in the coil, 5 is Magnetic flux interlinking with the coil. In FIG. 7, the voltage induced in the coil is

It is. Therefore, the voltage generated in the resonant circuit is

It becomes. Substituting equation 1 into equation 2,

It becomes. This is equivalent to the circuit shown in FIG.

である。コイルが小さくなる分、コイルに誘起する電圧も比例して小さくなる。FIG. 9 is a diagram for explaining an active coil antenna according to the first aspect of the invention. 1 is a coil having an inductance of (1-G) · L, 2 is a capacitor having a capacitance of C, and 3 is a loss resistance having a resistance value of R. Reference numeral 4 denotes an amplifier having a gain of G, reference numeral 5 denotes a voltage source induced in the coil, and reference numeral 6 denotes a magnetic flux linked to the coil. In FIG. 9, the voltage induced in the coil is

It is. As the coil becomes smaller, the voltage induced in the coil also becomes smaller proportionally.

のコイルに

のアンテナ誘起電圧が生じたことと等価であることを意味しているから、共振回路に発生する電圧は、

となる。式７に式４を代入すると、

となる。これを展開すると、

となって

となり、式３と全く同じになる。However, since the voltage source through the amplifier enters in series, FIG. 9 is equivalent to FIG. Figure 10 shows the inductance

Coil of

This means that the antenna induced voltage is equivalent to that generated, so the voltage generated in the resonant circuit is

It becomes. Substituting equation 4 into equation 7,

It becomes. If you expand this,

Become

And exactly the same as Equation 3.

  That is, it was proved that the active coil antenna shown in FIG. 9 is exactly the same as the conventional passive coil antenna shown in FIG. This is very noteworthy, that even if the active coil antenna is a small coil, it resonates at the same frequency as the passive coil antenna using a large coil and has the same antenna sensitivity.

でよいことを意味している。即ち、イメージ的に表現すれば、図１１に示すパッシブコイルアンテナと図１２に示すアクティブコイルアンテナは、共振周波数もアンテナ感度も全く同じ性能のコイルアンテナということになり、小型で高感度のコイルアンテナを必要とする電波腕時計などにとっては非常に価値のある発明である。図１１と図１２におけるインダクタンスＬ、キャパシタンスＣ及び抵抗値Ｒはそれぞれ同じ値である。For example, if the gain of the amplifier is 0.9990, the inductance of the coil is

Means that That is, in terms of an image, the passive coil antenna shown in FIG. 11 and the active coil antenna shown in FIG. 12 are coil antennas having the same performance in both resonance frequency and antenna sensitivity, and are small and highly sensitive coil antennas. This is a very valuable invention for radio-controlled wristwatches that need to operate. The inductance L, capacitance C, and resistance value R in FIGS. 11 and 12 are the same values.

となって、増幅器の開放利得によって制限を受ける。即ち増幅器の開放利得が１０の６乗であれば、コイルのインダクタンスは百万分の１まで小さくすることが出来るがそれ以上は不可能ということである。According to the present invention, it is shown that if the gain G amplifier and the coil are combined, the inductance of the coil can be made infinitely small by setting the gain G. However, if you take a closer look,

And is limited by the open gain of the amplifier. In other words, if the open gain of the amplifier is 10 to the sixth power, the inductance of the coil can be reduced to one millionth, but it cannot be further.

  The active coil antenna forms a feedback circuit. It is well known that the feedback circuit becomes unstable if the phase and amplitude characteristics of the feedback path are inappropriate. However, Nyquist's determination method proves that the active coil antenna of the present invention is a stable feedback circuit. FIG. 13 is a diagram showing a high-frequency equivalent circuit of a feedback path, wherein 1 is a coil having an inductance L, 2 is a tuning capacitor having a capacitance C, 3 is a loss resistor having a resistance value R, and 4 is a feedback amplifier having a gain G. It is.

ループ利得Ｇ・βのナイキスト軌跡を求めると図１４になる。In FIG. 13, the transfer function β of the feedback path and the loop gain G · β are expressed by the following equations.

FIG. 14 shows the Nyquist locus of the loop gain G · β.

であるから、Ａが無限に大きくなるに従ってＧは無限に＋１に近づくが、＋１以上には決してならない。従って、このナイキスト軌跡は点（１，ｊ０）の極めて近い内側を通過し点（１，ｊ０）を内側には含まない。故に、帰還係数が１の負帰還増幅器を用いた場合、ナイキストの判定法からこの帰還ループは安定であると言える。Here, a case where a negative feedback amplifier having a feedback coefficient of 1 is used as the gain G amplifier will be described. In FIG. 15, when the open gain of the amplifier is A,

Therefore, as A increases indefinitely, G approaches +1 infinitely, but never exceeds +1. Therefore, this Nyquist trajectory passes inside very close to the point (1, j0) and does not include the point (1, j0) inside. Therefore, when a negative feedback amplifier having a feedback coefficient of 1 is used, this feedback loop can be said to be stable from the Nyquist decision method.

  Next, the signal-to-noise ratio of the antenna output will be described. Even if the electromotive forces induced in the antenna are exactly the same, it is meaningless if the signal-to-noise ratio is bad. It will be described that the active coil antenna of the present invention is the same as the passive coil antenna in that respect.

で表され、全く同じである。ここで、ｋはボルツマン定数、Ｔは絶対温度、Ｂは雑音帯域幅、ν_ｎとｉ_ｎは増幅器の等価入力雑音電圧及び電流である。FIG. 16 is a diagram in which an equivalent input noise source generated from an amplifier and a resistor is added to the equivalent circuit diagram of the passive coil antenna of FIG. FIG. 17 is a diagram in which an equivalent input noise source generated from an amplifier and a resistor is added to the equivalent circuit diagram of the active coil antenna of FIG. In either case, the signal-to-noise ratio S / N is

And is exactly the same. Here, k is the Boltzmann constant, T is the absolute temperature, B is the noise bandwidth, [nu _n and i _n is the equivalent input noise voltage and current of the amplifier.

となる。Also, if Q is very high and there is no loss resistance, R can be infinite.

It becomes.

となる。ここで

ある。In general, when designing a resonant circuit, the inductance and capacitance are determined according to design requirements, but the bandwidth varies depending on the distribution even at the same resonant frequency. The distribution relationship among the bandwidth BW, inductance, and capacitance will be described. Expanding Equation 10

It becomes. here

is there.

となる。この式は、同じ（ω／ω_０）に対してＬが小さければν_０が小さくなることを示しているから帯域幅が狭い特性になる。一方Ｌが大きければその逆になることを示しているから帯域幅が広い特性になる。即ち、帯域幅はインダクタンスＬに比例している。First, if the resonator has no loss resistance, Q is infinite.

It becomes. This equation shows that if L is small for the same (ω / ω ₀ ), ν ₀ becomes small, so the bandwidth is narrow. On the other hand, if L is large, the reverse is indicated, so that the bandwidth is wide. That is, the bandwidth is proportional to the inductance L.

となる。従って、インダクタンスを大きくし、キャパシタンスを小さくして共振させると図１８のように帯域幅が広くなり、インダクタンスを小さくし、キャパシタンスを大きくして共振させると図１９のように帯域幅は狭くなる。Actually, since there is a loss resistance, Q becomes a finite value. If the -3 dB width is BW (-3 dB),

It becomes. Therefore, when the inductance is increased and the capacitance is reduced to resonate, the bandwidth is widened as shown in FIG. 18, and when the inductance is reduced and the capacitance is increased to resonate, the bandwidth is reduced as shown in FIG.

  From the above, it can be said that if the resonance circuit is configured with the inductance as large as possible and the capacitance as small as possible, the resonance frequency band is widened and the antenna circuit is stable against frequency fluctuations. Further, increasing the inductance increases the antenna electromotive force induced in the coil, which is preferable in terms of antenna sensitivity.

  For example, if the tuning capacitor is 100 pF and the loss resistance is 100 KΩ, the width of −3 dB from Equation 27 becomes 100 KHz, and there is no need to worry about frequency fluctuations. However, when the inductance cannot be increased as in the case of the passive coil antenna, it is necessary to increase the capacitor. For example, when the capacity is 10,000 pF, the bandwidth becomes 1 KHz, and it is necessary to perform temperature compensation. The active coil antenna of the present invention has an advantage that the bandwidth can be sufficiently wide since a large inductance can be obtained equivalently even with a small coil.

  There are two methods for changing the resonance frequency: a method for changing the equivalent inductance, and a method for changing the capacitance. Explain which is a smart choice.

  Equation 1 shows that the voltage induced in the antenna coil is proportional to the inductance. In the active coil antenna, the coil itself is fixed, and the inductance is equivalently changed by changing the gain of the amplifier. However, as shown in Equation 6, the voltage induced in the equivalent inductance is proportional to the gain G.

  Equation 27 shows that when the resonance frequency is changed with the inductance fixed, the bandwidth changes in proportion to the square of the frequency. That is, when the resonance frequency is changed from 60 KHz to 40 KHz, the bandwidth is narrowed down to 2.25 when the inductance is fixed and varied by the capacitor. Equation 27 shows that it is determined by a fixed capacitance and loss resistance and does not depend on variable inductance.

  In summary, when the inductance is fixed and the capacitance of the capacitor is changed to change the frequency from 60 KHz to 40 KHz, the bandwidth becomes less than half and the antenna sensitivity also deteriorates. On the other hand, the capacitance is fixed and the gain of the amplifier is reduced. If the inductance is changed by changing the frequency and the frequency is changed from 60 KHz to 40 KHz, the bandwidth does not change and the antenna sensitivity does not deteriorate. Therefore, it is better to change the frequency by fixing the capacitance and changing the equivalent inductance.

  The active coil antenna can increase the inductance of a small coil as much as possible by bringing the gain of the amplifier as close as possible to +1. Accordingly, the degree of freedom in product design is increased, and it is possible to realize a small and convenient portable receiver.

  Even if a small coil is used for the active coil antenna, the antenna sensitivity is exactly the same, and the receiving frequency can be easily changed by changing the gain of the amplifier within a range of less than +1 or by changing the capacitance of the capacitor. Is.

  In addition, the active coil antenna of the present invention forms a resonance circuit with a very large equivalent inductance, and thus has a wide bandwidth, and fundamentally solves the problem of frequency fluctuation due to changes in temperature and surrounding electromagnetic environment, which has been difficult until now. It can be solved.

Furthermore, an equivalently large inductance can be obtained with a small coil, so that it is possible to standardize the receiver unit for the radio timepiece, and to mass-produce inexpensive radio timepieces.

FIG. 20 shows an embodiment of an active coil antenna according to the first aspect of the present invention. 1 is an antenna coil, 2 is a capacitor, 3 is a feedback amplifier, and 4 is a bias control circuit. The feedback amplifier can be realized with a triple V _BE power supply. In order to prevent deterioration of the antenna sensitivity, the input stage bias is set to a constant current source bias having a bias control circuit to increase the input impedance and increase the Q of the antenna resonator. The gain of the amplifier is determined by the resistance value r and R _1.

  FIG. 21 shows an embodiment of the active coil antenna according to the second aspect of the present invention. A switch 5 for changing the gain of the amplifier is added to the active coil antenna of FIG. It is the figure which showed the method of varying a frequency.

  If the resonance frequency of the antenna resonance circuit is 40 KHz and the capacitance of the capacitor is 100 pF, an inductance of about 160 mH is required. If the gain G of the amplifier is set to 0.9990 in order to realize this with an active coil antenna, the inductance is reduced to 1 / 1000th of 160 μH.

となって、目的を達成する。Accordingly, the resistance value r 10 [Omega, when the _{R 1} to 10 k.OMEGA,

And achieve the purpose.

であるから４．３３ＫΩとなる。Further, if the resonance frequency of the antenna resonance circuit is 60 KHz and the capacitance of the capacitor is fixed to 100 pF, the inductance is required to be about 70 mH. If this is to be realized at the same 160 μH, the gain G of the amplifier may be changed to 0.9977. The resistance value R ₂ at that time is

Therefore, it becomes 4.33 KΩ.

  Therefore, an active coil antenna capable of dealing with both reception frequencies can be realized with a small inductance of 160 μH by switching the resistance according to the frequency control signal.

  FIG. 22 shows an embodiment of the active coil antenna according to the third aspect of the present invention, and is a diagram showing a method of changing the resonance frequency by adding a switch 5 for switching a capacitor to the active coil antenna of FIG. However, as described above, it reduces the bandwidth and deteriorates the antenna sensitivity, and should be adopted only when there are special design factors.

  FIG. 23 shows an embodiment of a radio-controlled timepiece receiver according to the fourth aspect of the present invention. 1 is an active bar coil antenna according to the present invention, 2 is an RF amplifier, 3 is an RF mixer, 4 is a local signal generator, 5 is a BPF, 6 is a crystal filter, 7 is an IF amplifier, 8 is a detector, and 9 is A / D converter, 10 is a microcomputer, and 11 is a PLL synthesizer. The 5 BPF removes unnecessary waves in a wide band, and the 6 crystal filter removes unnecessary waves in a narrow band. The ten microcomputers issue accessory drive signals based on the received signals to drive the motors for displaying the seconds, minutes, hours, days and months.

  Also in the loop type coil antenna, even when a considerable number of turns are required as shown in FIG. 2 in the prior art, if the active loop type coil antenna according to the present invention is used, as shown in FIG. A loop-type active coil antenna with the same performance can be realized with a single turn.

  As described in the embodiment, the realization of a very low frequency radio wave clock antenna in the LF band with a very small coil increases the freedom of design of the radio clock and makes it easy for small radio watches for women. realizable.

  Moreover, if it is used as a bar antenna for a portable AM radio, it is possible to realize a radio that has the same sensitivity and is smaller than the conventional one. In addition, the range of composite products can be expanded by incorporating a small radio in the mobile phone.

  Diagram showing a conventional bar coil antenna   Diagram showing a conventional loop coil antenna   Equivalent circuit diagram of conventional coil antenna   The figure which shows the bar-shaped coil antenna by this invention   The figure which shows the loop type coil antenna by this invention   Equivalent circuit diagram of coil antenna according to the present invention   The figure explaining the voltage source induced in the conventional coil antenna   Equivalent circuit diagram of conventional coil antenna   The figure explaining the voltage source induced in the coil antenna by this invention   Equivalent circuit diagram of the coil antenna shown in FIG.   Image of conventional bar coil antenna   Image of bar coil antenna of the present invention   Diagram showing the return path   Nyquist trajectory map   Diagram showing feedback amplifier   Diagram explaining equivalent noise of passive coil antenna   Diagram explaining equivalent noise of active coil antenna   Diagram showing characteristics of narrowband resonant circuit   Diagram showing characteristics of broadband resonant circuit   The figure which shows the Example of the active coil antenna by invention of Claim 1   The figure which shows the Example of the active coil antenna by invention of Claim 2   The figure which shows the Example of the active coil antenna by invention of Claim 3   The figure which shows the Example of the receiver for radio timepieces by the invention of Claim 4

Claims (4)

  One end of the coil antenna is connected to the input end of the amplifier whose gain is less than +1, the input impedance is sufficiently large and the output impedance is sufficiently small, the other end of the coil antenna is connected to the output end, and the amplifier input An active coil antenna comprising an antenna resonance circuit in which one end of a capacitor is connected to one end and the other end of the capacitor is grounded.   One end of the coil antenna is connected to the input end of the amplifier whose gain is less than +1, the input impedance is sufficiently large, and the output impedance is sufficiently small, the other end of the coil antenna is connected to the output end, and the amplifier input One end of the capacitor is connected to the other end, the other end of the capacitor is grounded to form an antenna resonance circuit, and the gain of the amplifier can be varied within a range of less than +1, so that the resonance frequency of the antenna resonance circuit can be varied. An active coil antenna characterized by that.   One end of the coil antenna is connected to the input end of the amplifier whose gain is less than +1, the input impedance is sufficiently large, and the output impedance is sufficiently small, the other end of the coil antenna is connected to the output end, and the amplifier input One end of a capacitor is connected to the other end, the other end of the capacitor is grounded to form an antenna resonance circuit, and the capacitance of the capacitor can be varied to change the resonance frequency of the antenna resonance circuit. Active coil antenna.   A receiver using an active coil antenna according to any one of claims 1 to 3.

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