JP2008172761A - Variable inductance type resonance circuit and broadcasting receiving using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for achieving a variable inductance type resonance circuit and to provide a means for solving the improvement of sensitivity in an on-board broadcasting receiver and the improvement of interference wave removing capacity. <P>SOLUTION: An LC resonance circuit variably changes the inductance of an inductive element by combining an amplifier and the inductive element and allowing the gain of the amplifier to electronically vary in a range less than +1. The LC resonance circuit is used as a tuning circuit capable of allowing a required frequency band to vary even when antenna capacity exists and as an oscillator in a local signal generator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is an elemental technology that has been an obstacle to realizing small size, high sensitivity, and high selectivity in a broadcast receiver, and an LC resonance circuit that can be varied over a wide range at a low voltage, and broadcast reception using the LC resonance circuit. Related to the machine.

  The most hindrance of the in-vehicle AM broadcast receiver is that it is not possible to provide a tuning circuit that can be varied according to the reception frequency at the antenna input stage of the receiver due to the conditions specific to the in-vehicle antenna. there were.

  Further, in a broadband broadcast receiver covering the LW to SW band, it is impossible to provide a tuning circuit in the RF stage as well as the antenna input stage.

  In the prior art, the LC resonance circuit is composed of a fixed inductance and a variable capacitance diode. The variable capacitance range of the variable capacitance diode is a voltage of 0 to 8 V and a range of 20 times from 500 pF to 25 pF, which is about 4.5 times when converted into a frequency variable range. With this rate of change, the AM receiver frequency of 522 KHz to 1,710 KHz can be sufficiently accommodated at least.

  However, since the in-vehicle antenna is an element that is extremely short compared to the wavelength of the reception frequency, it has a high impedance, and is designed to be connected to the receiver via a 1 m coaxial cable. It becomes an equivalent circuit.

  In FIG. 1, 1 is an antenna electromotive force, 2 is 75Ω as an antenna signal source resistance, 3 is an antenna capacitance of 15 pF, and 4 is a cable capacitance of 65 pF. It is a standard that has been agreed in the domestic and foreign industries to provide compatibility between radio receivers and in-vehicle radio antennas.

  This means that a total of 80 pF of the antenna capacity 15 pF and the cable capacity 65 pF is added when viewed from the tuning circuit at the front end of the receiver, and the range of the variable capacity is equivalently from 105 pF to 580 pF. It will be reduced from the double to the range of only 5 times.

  When this is converted into a variable frequency range, it is substantially compressed by about 2.3 times, and the tuning circuit of the antenna stage cannot cope with the frequency of the AM receiver.

  In order to solve this problem, a method of providing a plurality of coils as shown in FIG. 2, switching these coils according to the reception frequency, and expanding the frequency variable range has been used.

  In FIG. 2, 1 and 2 are coils, 3 is a variable capacitance diode, 4 is a switch, 5 is a switch control signal, 6 is a buffer resistor, and 7 is a frequency control voltage from a PLL synthesizer.

  For example, if the coil switching method has three tuning circuits in the front end and one oscillation circuit in the local signal generator, and each frequency is changed while switching two coils, Eight were needed, and the size was inevitably increased.

  However, in the era when various options such as cassettes, CDs, MDs, and car navigations are installed in the car, the receiver is also required to be downsized, and the coil switching method has not been put into practical use as a method that does not match the times.

  As a result, the tuning circuit of the antenna stage, which is the most basic for the receiver, was abandoned, and the received signal from the antenna was simply received by a high impedance RF amplifier. As a result, it has sacrificed high sensitivity and high ability to remove interference, which is the most important performance for the receiver.

  FIG. 3 shows a front end of a conventional typical in-vehicle AM broadcast receiver. 1 is an equivalent circuit of the vehicle-mounted antenna shown in FIG. 1, 2 is an RF amplifier, 3 and 4 are tuning circuits, 5 is an RF mixer, 6 is a local signal generator, 7 is an intermediate frequency signal output, and 8 is supplied from a PLL synthesizer 9 is a fixed choke coil, which has a resonance point around 300 KHz with a total of 80 pF of antenna capacity 15 pF and cable capacity 65 pF. Inserted for the purpose of damping.

  As described above, in the conventional in-vehicle AM broadcast receiver, the variable frequency tuning circuit is provided at the rear stage of the RF amplifier, but is not provided at all at the front stage. Therefore, as shown in FIG. 4, the antenna stage has completely unprotected characteristics against the interference wave, which is a serious drawback.

  The loss caused by the absence of a tuning circuit that varies depending on the reception frequency in the antenna stage is in addition to the loss of 14.5 dB that is lost due to the capacitance division of 15 pF and 65 pF, in addition to the normal gain obtained by the Q of the tuning circuit. The total value is as large as 20 dB or more.

  A conventional receiver that abandons having a high ability to eliminate interference at the antenna stage causes interference due to overloading of the RF amplifier when a strong interference is present. In order to avoid this, the AGC circuit strongly attenuates the antenna stage, and as a result, the receiver has a so-called sensitivity suppression in which the desired wave is also attenuated simultaneously.

  In recent years, in-vehicle broadcast receivers for Europe have become mainstream not only for MW band AM broadcasting but also for broadband broadcast reception from the LW band to the SW band.

  However, wideband broadcast receivers from the LW band to the SW band have a reception frequency range from 150 KHz to 22 MHz, and the frequency ratio is nearly 150 times, so when converted to a variable capacity ratio, this is more than 20,000 times and is very variable. It is impossible to realize a tuning circuit and an oscillation circuit with a capacitive diode.

  Therefore, the broadband broadcast receiver from the LW band to the SW band is a broadcast receiver in which a tuning circuit cannot be provided not only in the antenna stage but also in the RF stage.

  The present invention provides a means for realizing a broadcasting receiver having a tuning circuit having high selectivity in the antenna stage and the RF stage, and having high sensitivity and high interference wave elimination capability. It solves the shortcomings.

  The invention according to claim 1 is a variable inductance type resonance that can be varied in a wide band at a low voltage by combining an amplifier capable of electronically varying the gain, a coil and a capacitor, and varying the voltage gain of the amplifier within a range of less than +1. It is to provide a circuit.

  According to a second aspect of the present invention, there is provided means for realizing a receiver having a high sensitivity and a high interference wave removing capability by using the variable inductance type resonance circuit according to the first aspect of the present invention for a front end of a broadcast receiver. There is.

  The principle of the variable inductance type resonance circuit according to claim 1 will be described with reference to a circuit diagram shown in FIG.

  In FIG. 5, 1 is a coil having an inductance L, 2 is a capacitor having a capacitance C, 3 is a sufficiently high input impedance, sufficiently low output impedance, and electronically variable within a range where the voltage gain G is less than +1. A possible amplifier 4 is a frequency control signal from a PLL synthesizer.

  If the input impedance of the amplifier is infinite and the output impedance is zero, the circuit in FIG. 5 is equivalent to the circuit in FIG. The principle of the variable inductance type resonance circuit as the basis of the present invention will be described with reference to FIGS.

であり、コイルＬに流れる電流は

となる。The current flowing through the capacitor C is

And the current flowing through the coil L is

It becomes.

ここで

である。Therefore, the admittance of the parallel resonant circuit is expressed by the following equation.

here

It is.

  As is clear from Equation 3, the circuit shown in FIG. 6 is proved to be a parallel resonant circuit equivalent to FIG. In FIG. 7, 1 is a coil of L 'whose inductance is represented by Equation 4, and 2 is a capacitor having the same capacitance as 2 in FIG.

  FIG. 8 shows an equivalent circuit when the input impedance of the external load or variable gain amplifier is finite. This is actually the case. In FIG. 8, 1 is a coil having an inductance L ', 2 is a capacitor having a capacitance C, and 3 is a resistor having a resistance value R.

で与えられ、増幅器の利得を＋１未満の範囲で可変することによってω_０中心にして、無限小から無限大の角周波数まで可変できる。If the angular frequency at which resonance is caused by the fixed inductance L and the fixed capacitance C is ω ₀ , the resonance angular frequency ω _r of the variable inductance type resonance circuit is

By varying the gain of the amplifier within a range of less than +1, the angular frequency can be varied from infinitesimal to infinite with ω _{0 as the} center.

  The variable inductance type resonance circuit according to claim 1 forms a feedback circuit including an amplifier. The feedback circuit is unstable and oscillates if the phase vs. amplitude characteristic of the feedback path is inappropriate. However, it is proved by the Nyquist determination method that the variable inductance type resonance circuit of the present invention is a stable feedback circuit.

ここで、ループ利得Ｇ・βのナイキスト軌跡を求めると図１０になる。このナイキスト軌跡は、増幅器の利得Ｇが＋１未満であるから点（１，ｊ０）を内側に囲まない。従って、このインダクタンス可変型共振回路は安定である。In FIG. 9, 1 is a coil having an inductance L, 2 is a capacitor having a capacitance C, 3 is a load resistor having a resistance value R, and 4 is a variable gain amplifier having a gain G of less than +1. The transfer function β of the feedback path and the loop gain G · β are expressed by the following equations.

Here, FIG. 10 shows the Nyquist locus of the loop gain G · β. This Nyquist trajectory does not surround the point (1, j0) because the amplifier gain G is less than +1. Therefore, this inductance variable resonance circuit is stable.

  This is a very important finding, and it has been proved that the variable inductance type resonance circuit according to claim 1 is a stable system even though the feedback gain exceeds +1.

Moreover, this variable inductance type resonance circuit can vary the frequency over a wide band even at a low voltage. this,
0 ≦ G <+1
This will be described with reference to the embodiment of FIG.

  In FIG. 11, 1 is a coil having an inductance L, 2 is a capacitor having a capacitance C, 3 is an amplifier whose input impedance is sufficiently high, output impedance is sufficiently low, and gain can be varied within a range from 0 to less than +1. Is a preamplifier with a gain of +1 combined with 31 transistors, 32 is a postamplifier with a gain of +1 combined with 33 transistors, 34, 35 and 36 are constant current sources, 37 and 38 are current mirror circuits, 39 And 40 are differential circuits, 41 is a constant voltage source, 42 and 43 are resistors that determine the maximum gain of the amplifier 3, 44 is a resistor that compensates for DC offset due to the base current of the post-amplifier, and 45 is a gain control signal for the amplifier 3 Input terminal.

In FIG. 11, if the current amplification factor of the transistor is sufficiently large and the resistors 42 and 43 have the same resistance value R, the gain of the amplifier can be varied from 0 to +1 by the control signal input to the terminal 45. It will be proved by the following formula that the resonance frequency can be varied from ω ₀ to an infinitesimal angular frequency.

となる。Since the signal at the positive terminal of the preamplifier 30 appears at the emitter of the transistor 31, if the resistance value of 42 and 43 is R, the signal current flowing through the collector of the 31 transistor is

It becomes.

である。ここで

であり、Ｖ_ｉｄは利得制御電圧、Ｖ_Ｔはデバイスのサーマル電圧で通常２６ｍＶである。This signal current is divided into i ₁ and i ₂ by a differential circuit 39 via a current mirror circuit 37. That is

It is. here

Where V _id is the gain control voltage and V _T is the device thermal voltage, which is typically 26 mV.

であるから、利得Ｇは

となって、数式５から共振角周波数は

となる。Therefore, if i ₁ is represented by i ₀

Therefore, the gain G is

From Equation 5, the resonance angular frequency is

It becomes.

となって、ＬＷ帯の１５０ｋＨｚからＳＷ帯の４．８ＭＨｚまで可変可能である。FIG. 12 shows the calculation result. In this calculation range

Thus, it can be varied from 150 kHz in the LW band to 4.8 MHz in the SW band.

で変化率を計算してみると

となり、ＬＷ帯の１５０ＫＨｚからＳＷ帯の２２．２ＭＨｚまで制御電圧が±２６０ｍＶの範囲で可変できることになる。Expand the scope further

When calculating the rate of change with

Thus, the control voltage can be varied in the range of ± 260 mV from 150 KHz in the LW band to 22.2 MHz in the SW band.

  This is very remarkable, and the variable inductance type resonance circuit of the present invention has been found to have a much wider variable range than a conventional resonance circuit using a variable capacitance diode even at a low voltage.

  In addition, if this is utilized, the present invention can also provide a tuning circuit for a broadband broadcast receiver from the LW band to the SW band, which has not been able to provide a tuning circuit until now. It was discovered that a broadcasting receiver having the capability can be realized.

  Also, the tuning circuit may be required for full tap or secondary coupling. FIG. 13 shows an example of full tap coupling, and FIG. 14 shows an example of secondary coupling. Since the variable inductance resonator can supply a bias voltage from the output of the post-amplifier of the variable gain amplifier, it can be directly connected to the collector of the transistor.

  For a variable gain amplifier used in a variable inductance type resonant circuit, if the input impedance is not sufficiently high compared to the impedance of the capacitor, the resistance is equivalent to the state connected in parallel with the capacitor, and the output impedance is If it is not sufficiently low compared to the impedance of the coil, it is equivalent to a state in which a resistor is connected in series with the coil, and the no-load Q of the resonance circuit is dumped, which hinders improvement in sensitivity and interference wave removal capability. . Therefore, it is desirable to use a negative feedback amplifier or the like.

  When the linearity of the variable gain amplifier used in this resonant circuit is poor, modulation distortion occurs in the tuning circuit if there is an overload reception input. Therefore, it is necessary to use a variable gain amplifier with good linearity. In the embodiment shown in FIG. 11, since a feedback gain variable circuit including an operational amplifier is used, the linearity is excellent.

  FIG. 15 shows an embodiment in which the variable inductance type resonance circuit according to claim 1 is used for an oscillation circuit. In FIG. 15, reference numeral 1 denotes the variable inductance type resonance circuit according to claim 1 shown in the embodiment of FIG. 11, and 2 denotes a differential amplifier.

  Further, the preamplifier of the variable gain amplifier has an advantage that it can also be used as an RF amplifier with AGC gain control. FIG. 16 shows an embodiment thereof. 1 is a coil, 2 is a capacitor, 3 is the same gain variable amplifier as shown in FIG. 11, 30 is a gain control signal input terminal, 4 is an RF amplifier with AGC gain control, 40 is a transistor, and 41 is gain controlled by an AGC signal A differential circuit to be performed, 42 is an input terminal for AGC gain control voltage, and 43 is a collector output terminal.

  Further, the preamplifier of the variable gain amplifier has an advantage that it can also be used as an RF mixer. FIG. 17 shows an embodiment thereof. 1 is a coil, 2 is a capacitor, 3 is the same gain variable amplifier as shown in FIG. 11, 30 is a gain control signal input terminal, 4 is an RF mixer, 40 is a transistor, and 41 is a differential circuit that performs switching operation by a locally generated signal , 42 is an IF tuning circuit, and 43 is an IF output terminal.

  In the embodiment of FIGS. 16 and 17, since the transistor 40 is connected in parallel to the output of the preamplifier, the resistance value is R / 2.

  The broadcast receiver according to claim 2 uses the variable inductance type resonance circuit according to claim 1 for the tuning circuit of the front end and the oscillation circuit of the local signal generator, and has the disadvantages of the conventional broadcast receiver. Can be fundamentally solved.

  FIG. 18 is a diagram showing a conventional in-vehicle AM broadcast receiver, wherein 1 is the same antenna equivalent circuit as shown in FIG. 1, 3 is an RF amplifier, 4 and 6 are tuning circuits using variable capacitance diodes, and 7 is RF. Mixer, 8 is an intermediate frequency ceramic filter, 9 is an IF amplifier, 10 is a detector, 11 is an audio amplifier, 12 is a speaker, 13 is an AGC control signal generator, 14 is an AGC signal, 15 is a local signal generator, 16 is a PLL synthesizer, 17 is a crystal oscillator that generates a reference signal, 18 is a control voltage of a variable capacitance diode used in a front end tuning circuit and an oscillation circuit of a local signal generator, and 19 is a power supply ham for a high-voltage transmission line. It is a choke coil.

  In a conventional in-vehicle AM receiver, a tuning circuit can be provided in the RF stage, but a frequency variable tuning circuit cannot be provided in the antenna stage.

  FIG. 19 is a diagram showing a conventional wideband broadcast receiver from the LW band to the SW band. 1 is the same antenna equivalent circuit as shown in FIG. 1, 3 is an RF amplifier, 4 is an LPF, and 5 is a first intermediate frequency. RF mixer for converting to 1, crystal filter for first intermediate frequency, 7 RF mixer for converting to second intermediate frequency, 8 for ceramic filter for second intermediate frequency, 9 for IF amplifier, 10 for detector, 11 for Audio amplifier, 12 speaker, 13 AGC control signal generator, 14 AGC signal, 15 first local signal generator, 16 PLL synthesizer, 17 crystal oscillator generating reference signal, 19 high voltage power line 20 is a second local signal generator that attenuates the power supply hum.

  Normally, 10.7 MHz is used as the first intermediate frequency, and 450 KHz is used as the second intermediate frequency in the same manner as in the AM broadcast receiver, so 10.25 MHz is selected as the 20 second local signal generator.

  Conventional broadband broadcast receivers from the LW band to the SW band are limited to variable-capacitance diodes and cannot provide tuning circuits not only in the antenna stage but also in the RF stage.

  FIG. 20 is a diagram showing an embodiment of a receiver for broadband broadcasting from the LW band to the SW band according to claim 2, wherein 1 is the same antenna equivalent circuit as shown in FIG. 1, 2, 4 and 6 are claims 1 Tuning circuit using the described variable inductance type resonance circuit, 3, 5 RF amplifier, 7 RF mixer, 8 medium frequency ceramic filter, 9 IF amplifier, 10 detector, 11 audio amplifier, 12 Speaker, 13 is an AGC control signal generator, 14 is an AGC signal, 15 is a local signal generator using a variable inductance type resonance circuit according to claim 1, 16 is a PLL synthesizer, and 17 is a crystal oscillator that generates a reference signal , 18 are control voltages of the variable gain amplifier used in the front end tuning circuit and the oscillation circuit of the local signal generator.

  In this embodiment, it is possible to provide a tuning circuit in the antenna stage and the RF stage by using the variable inductance type resonance circuit according to the first aspect.

  In the old mechanical μ tuning era, a tuning circuit could be provided in the antenna stage, so the receiver sensitivity was good. However, since the tuning circuit cannot be provided in the antenna stage since the electronic tuning system using the variable capacitance diode is changed, the sensitivity of the receiver has to be deteriorated.

  The variable inductance type resonance circuit according to the first aspect solves this problem, and a tuning circuit can be provided again in the antenna stage. Therefore, an improvement in sensitivity of about 20 dB or more can be expected at all frequencies.

  By having a tuning circuit in the antenna input stage, it is possible to separate the desired wave and the undesired wave and avoid interference due to overloading of the antenna stage. Further, the choke coil for attenuating the power supply hum of the high-voltage transmission line 9 in FIG.

  2. A conventional tuning circuit using parallel resonance that varies the capacitance of a capacitor has a drawback that the bandwidth is wide in a high frequency range and narrow in a low frequency range. A tuning circuit using a variable inductance type resonance circuit has the advantage that the bandwidth changes at a constant value. This is proved by mathematical formulas.

であるから

となる。8, the goodness of the tuning circuit Q, BW angular frequency bandwidth of -3 dB, when the tuning angular frequency and omega _T

Because

It becomes.

  As shown in Formula 20, in a conventional resonant resonance tuning circuit in which a variable capacitance and a fixed inductance are combined, the bandwidth varies greatly in proportion to the square of the tuning angular frequency. The tuning circuit using is fixed at C and R, and the bandwidth is constant regardless of the tuning angular frequency.

  This is a very important factor for broadcast receivers. This is because the ability to reject interference does not change regardless of the broadcast frequency received.

  Looking at the relationship between AM broadcast frequency allocation and transmission power in major cities around the world, broadcast stations with low broadcast frequencies have high transmission power, and broadcast stations with high broadcast frequencies have low transmission power.

  However, since the bandwidth of the conventional capacitor variable tuning circuit is widened in a high frequency band, when receiving a high frequency broadcast wave, the broadcast wave of a low frequency high power transmission station cannot be sufficiently eliminated.

  The tuning circuit of the antenna stage using the variable inductance type resonance circuit according to claim 1 functions extremely effectively in that respect.

  Conventionally, an FET with good linearity was separately required as an RF amplifier. However, the amplifier with an AGC gain control circuit sharing the preamplifier of the variable inductance type resonance circuit according to claim 1 has excellent linearity by negative feedback. The amplifier is less likely to cause modulation distortion with respect to a plurality of strong interference waves.

  As for the RF mixer, the negative feedback type RF mixer sharing the preamplifier of the variable inductance type resonance circuit according to claim 1 is excellent in linearity and does not cause modulation distortion with respect to a plurality of strong interference waves.

  If the variable inductance type resonance circuit according to claim 1 is used, a variable frequency tuning circuit can be configured with a variable gain amplifier in an integrated circuit, so that a variable capacitance diode, which has been conventionally required, becomes unnecessary. The RF amplifier does not require a separate FET, and a choke coil that attenuates the power supply hum of the high-voltage power transmission line is not required.

  FIG. 11 shows an embodiment of the variable inductance type resonance circuit according to claim 1, wherein an amplifier whose gain is variable from 0 to less than +1 is used.

  FIG. 13 shows an embodiment of full-tap coupling of a tuning circuit using the variable inductance type resonance circuit according to claim 1.

  FIG. 14 shows an embodiment of secondary coupling of a tuning circuit using the variable inductance type resonance circuit according to claim 1.

  FIG. 15 shows an embodiment of an oscillation circuit of a local signal generator using the variable inductance type resonance circuit according to claim 1.

  FIG. 20 shows an embodiment of the broadcast receiver according to claim 2.

  The present invention has extremely high applicability particularly to an in-vehicle broadcast receiver and fundamentally solves the drawbacks of the antenna stage of a conventional receiver.

  The present invention can also be used in home and portable broadcast receivers.

  Diagram showing equivalent circuit of in-vehicle antenna   Diagram showing conventional coil switching method   The figure which shows the front end of the conventional typical vehicle-mounted AM broadcast receiver   Diagram showing the characteristics of a typical conventional antenna stage   The figure which shows the basic principle of the inductance variable type resonance circuit of Claim 1   Equivalent circuit diagram of the circuit shown in FIG.   Equivalent circuit diagram of the circuit shown in FIG.   Fig. 7 shows an external load applied to the resonant circuit shown in Fig. 7.   The figure which shows the feedback path of the inductance variable type resonance circuit of Claim 1   The Nyquist locus diagram of the variable inductance type resonance circuit according to claim 1.   The figure which shows the Example of the amplifier which can be changed in the range which the gain used for the variable inductance type resonance circuit of Claim 1 is 0 to less than +1   The figure which shows an example of the variable frequency range of the inductance variable type resonance circuit of Claim 1   The figure which shows the Example of the full tap coupling of the tuning circuit using the inductance variable type resonance circuit of Claim 1   The figure which shows the Example of the secondary coupling of the tuning circuit using the inductance variable type resonance circuit of Claim 1   The figure which shows the oscillation circuit using the inductance variable type resonance circuit of Claim 1   The figure which shows the Example which combines the preamplifier of the gain variable amplifier of the variable inductance type | mold resonant circuit of Claim 1 with RF amplifier with AGC gain control   The figure which shows the Example which uses the preamplifier of the variable gain amplifier of the variable inductance type | mold resonance circuit of Claim 1 as an RF mixer.   The figure which shows the conventional typical in-vehicle AM broadcast receiver   The figure which shows the conventional receiver for broadband broadcasting from typical LW band to SW band   The figure which shows the Example of the vehicle-mounted broadcast receiver of Claim 2.

Claims (2)

  One end of the inductive element is connected to the input end of the amplifier having a sufficiently high input impedance and a sufficiently low output impedance, the other end of the inductive element is connected to the output end, and a capacitive element is connected to the input end of the amplifier. One end of the resonant circuit is connected, the other end of the capacitive element is grounded to form a resonant circuit, and the voltage gain of the amplifier can be varied within a range of less than +1, thereby making the resonant frequency of the resonant circuit variable. A variable inductance type resonance circuit.   A broadcast receiver, wherein the variable inductance type resonance circuit according to claim 1 is used for a tuning circuit of a receiver and an oscillation circuit of a local signal generator.

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