JP2009225411A - Broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implement an on-vehicle broadcast receiver equipped with a tuned circuit at an antenna stage thereof, and to reduce production cost thereof by employing an oscillation circuit that does not use a coil for a local signal generator. <P>SOLUTION: A preamplifier and a postpositive amplifier having a voltage gain that is less than +1 and is as near as possible to +1, a sufficiently high input impedance, and a sufficiently low output impedance are connected to a former stage and a subsequent stage of a high frequency pass filter that includes a capacitor and a first resistance. An input end of the preamplifier and an output end of the postpositive amplifier are connected through a second resistor to constitute a virtual inductance. An oscillation circuit using the virtual inductor and the tuned circuit using the coil are controlled together by the same voltage supplied by a PLL synthesizer and are implemented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention mainly relates to an improvement in an antenna stage circuit and a local signal generator of an in-vehicle broadcast receiver.

  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.

  In the prior art, the tuning circuit is composed of a coil 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. This is a standard determined by ISO in order to provide compatibility between radio receivers and in-vehicle 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 reception band switching control signal, and 6 is a tuning voltage supplied from a PLL synthesizer.

  The tuning system of the broadcast receiver controls the frequency of the resonant circuit of the antenna stage, RF stage and local signal generator with the same voltage supplied from the PLL synthesizer, so that each resonant circuit maintains perfect consistency. Must be.

  Therefore, the RF stage and the local signal generator that are not affected by the antenna capacity and cable capacity need to use two coils in the same manner as the antenna stage.

  Therefore, the coil switching method has, for example, one resonance circuit for the antenna stage, two tuning circuits for the RF stage, and one resonance circuit for the local signal generator, and each frequency is changed while switching two coils. As a result, a total of eight was required, 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 antenna stage tuning circuit, which is the most basic for the receiver, is abandoned, the tuning circuit is provided only in the RF stage, and the antenna stage simply receives the received signal with a high impedance RF amplifier. Did not get. This is a big difference from home broadcast receivers, and it has remained a problem that has not been solved for decades.

  As a result, high sensitivity and high interference wave removal capability, which is the most important performance for mobile broadcast receivers such as in-vehicle use, have been sacrificed.

  FIG. 3 shows a front end circuit of a conventional typical in-vehicle AM broadcast receiver. 1 is an ISO antenna dummy circuit shown in FIG. 1, 2 is an RF amplifier, 3 and 4 are tuning circuits composed of a coil and a variable capacitance diode, 5 is an RF mixer, and 6 is composed of a coil and a variable capacitance diode. The resonance circuit of the local signal generator, 7 is an IF frequency signal output, 8 is a tuning voltage of a variable capacitance diode supplied from a PLL synthesizer, 9 is a fixed choke coil having a very large inductance, and has an antenna capacity of 15 pF and a cable capacity of 65 pF. It has a resonance point in the vicinity of about 300 KHz with a total of 80 pF, and is inserted for the purpose of attenuating a 50 Hz or 60 Hz power supply hum received from the high-voltage power transmission line.

  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 disturbing 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 was 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 also causes so-called sensitivity suppression in which the desired wave is also attenuated simultaneously.

  In a conventional broadcast receiver, the local signal generator is composed of a coil and a variable capacitance diode. Coils are the most expensive electronic component and hinder downsizing.

  The present invention provides a means for realizing a broadcasting receiver having a tuning circuit having high selectivity at an antenna stage, and having high sensitivity and high interference wave removal capability at a low price. It solves the shortcomings.

  According to the first aspect of the present invention, the voltage gain is less than +1 and is close to +1, the input impedance is sufficiently high, and the output impedance is high and low in the front and rear stages of the high-pass filter including the variable capacitance diode and the first resistor. Is connected to a preamplifier and a postamplifier that are sufficiently low, and the input terminal of the preamplifier and the output terminal of the postamplifier are connected by a second resistor to form a variable inductance virtual inductor, and the virtual inductor The antenna capacity and cable capacity or a capacitor including them constitutes a frequency variable resonance circuit to form an antenna stage tuning circuit of the receiver, and the antenna stage tuning circuit further includes an RF stage tuning composed of a coil and a variable capacitance diode. Means for implementing a broadcast receiver frequency controlled by the same voltage supplied from a PLL synthesizer with a circuit It is to provide.

  According to the second aspect of the present invention, in the front and rear stages of the high-pass filter comprising the variable capacitance diode and the first resistor, the voltage gain is less than +1 and close to +1, the input impedance is sufficiently high, and the output impedance Is connected to a preamplifier and a postamplifier that are sufficiently low, and the input terminal of the preamplifier and the output terminal of the postamplifier are connected by a second resistor to form a variable inductance virtual inductor, and the virtual inductor And a capacitor constitute a frequency variable resonance circuit to be a local signal generator of a receiver, and the local signal generator is supplied from a PLL synthesizer together with an RF stage tuning circuit including a coil and a variable capacitance diode. The present invention provides a means for realizing a broadcast receiver whose frequency is controlled by the voltage of the current.

  First, the virtual inductor described in claims 1 and 2 will be described. In FIG. 5, 1 is a variable capacitance diode having a capacitance of C, 2 is a first resistor having a resistance value of R, 3 is a second resistor having a resistance value of r, and 4 and 5 are sufficiently high in input impedance and output impedance. Is sufficiently low and the voltage gain is less than +1, and it is an amplifier close to +1.

である。従って、第二の抵抗に流れる電流は

となる。数式２から入力インピーダンスを求めると

となる。これを仮想インダクターと称する。可変容量ダイオードはＰＬＬシンセサイザーの同調電圧によって変化するから図５の等価回路は図６に示す可変型仮想インダクターになる。In FIG. 5, the output voltage of the post-amplifier is

It is. Therefore, the current flowing through the second resistor is

It becomes. When the input impedance is calculated from Equation 2,

It becomes. This is called a virtual inductor. Since the variable capacitance diode changes depending on the tuning voltage of the PLL synthesizer, the equivalent circuit of FIG. 5 is a variable virtual inductor shown in FIG.

  In FIG. 6, 1 is the loss resistance of the virtual inductor, 2 is the inductance of the virtual inductor, and 3 is a post-amplifier.

  Therefore, as shown in FIG. 7, if the virtual inductor and the antenna capacity and cable capacity are connected in parallel, the circuit becomes equivalent to the circuit shown in FIG. 8, and an antenna stage tuning circuit of the in-vehicle broadcast receiver can be realized. In FIG. 7, 1 is an antenna dummy circuit of an in-vehicle broadcast receiver of the ISO standard, and 2 is a virtual inductor.

  In an electronically tuned broadcast receiver, the resonant circuit of the antenna stage, RF stage and local signal generator is controlled by the tuning voltage supplied from the PLL synthesizer, and each must have perfect matching. That was mentioned above.

  However, a tuning circuit using a virtual inductor does not have a secondary coupling terminal unlike a tuning circuit using a coil. Therefore, there is an inconvenience that the degree of freedom of design is lacking, such as connecting the collector output of the amplifier to the secondary coupling terminal to set an appropriate gain.

  Therefore, the antenna stage is required to use a tuning circuit using a virtual inductor, and the RF stage is required to use a tuning circuit using a coil.

  FIG. 9 shows that the antenna stage tuning circuit using the virtual inductor and the RF stage tuning circuit using the coil can completely match the resonance frequency by the same tuning voltage supplied from the PLL synthesizer. I will explain.

In FIG. 9, reference numeral 1 denotes a tuning circuit using a coil used in the RF stage, where L is the inductance of the coil, and C is the capacitance of the variable capacitance diode controlled by the voltage from the PLL synthesizer. Reference numeral 2 denotes a tuning circuit using a virtual inductor used in the invention of claim 1. The capacitor constituting the high-pass filter is a variable capacitance diode controlled by the voltage from the PLL synthesizer, and its capacitance is C. The first resistor constituting the high-pass filter has a resistance value R. The resistance value of the second resistor connecting the input terminal of the preamplifier and the output terminal of the postamplifier is r. Further, the capacitance of the capacitor that constitutes the virtual inductor and the tuning circuit is C ₀ .

となる。一方２の仮想インダクターを用いた同調回路の共振角周波数は

となる。ここで

とおけば

になる。In FIG. 9, the resonance angular frequency of the tuning circuit using one coil is

It becomes. On the other hand, the resonance angular frequency of the tuning circuit using two virtual inductors is

It becomes. here

If you

become.

  This is a very big discovery, and the resonance circuit using the virtual inductor and the resonance circuit using the coil can be varied at the same frequency by the same voltage supplied from the PLL synthesizer even though the type of the resonance circuit is completely different. If this is used, it becomes possible to provide a tuning circuit in the antenna stage, which has been impossible in the past, and has high sensitivity and high selectivity. The machine can be realized.

  At the same time, if a resonance circuit using a virtual inductor is used for the oscillation circuit of the local signal generator, the tuning frequency of the RF stage and the oscillation frequency of the local signal generator are linked with the same voltage supplied from the PLL synthesizer. It has been found that it can be controlled, and if this is used, a local signal generator that does not use a coil can be realized, and a small and low-priced broadcast receiver can be realized.

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

  The invention described in claim 1 solves this problem and can provide a tuning circuit in the antenna stage again. Therefore, an improvement in sensitivity of about 20 dB or more can be expected at all frequencies.

  Further, 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.

  According to the second aspect of the present invention, the local signal generator that has conventionally used a coil eliminates the need for the coil and can contribute to the reduction in the cost and size of the receiver.

  FIG. 10 shows an embodiment of the preamplifier and the postamplifier used for the virtual inductor according to the first, second and third aspects. 1 is a resistor that determines the gain to the subsequent RF stage, 2 is a DC blocking capacitor, 3 is an AGC differential transistor, and 4 is an RF stage tuning circuit.

  FIG. 11 is a diagram showing an embodiment of the local signal generator of the receiver according to claim 2, wherein 1 is a resonance circuit using a virtual inductor, and the oscillation frequency is a voltage from a PLL synthesizer supplied to the variable capacitance diode. Is controlled.

  12 is a diagram showing a broadcast receiver according to claims 1 and 2, wherein 1 is an ISO standard antenna dummy circuit, 2 is a virtual inductor using a variable capacitance diode, 3 is an amplifier, 4 and 5 are a coil and a variable capacitance. RF stage tuning circuit composed of diode, 6 RF mixer, 7 local signal generator composed of virtual inductor using fixed capacitor and variable capacitance diode, 8 PLL synthesizer, 9 crystal oscillator, 10 antenna stage tuning Circuit, RF stage tuning circuit and frequency control voltage of local signal generator, 11 IF filter, 12 IF amplifier, 13 detector, 14 AGC signal generator, 15 AGC signal, 16 audio amplifier, 17 It is a speaker.

  FIG. 12 shows a feature in which a resonant circuit using a virtual inductor and a resonant circuit using a coil are both controlled by the same voltage supplied from a PLL synthesizer.

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

  Further, the invention described in claim 2 is very highly applicable to a PLL synthesizer type portable radio that is required to be downsized at a low price by eliminating the need for a coil.

  Diagram showing equivalent circuit of in-vehicle antenna   Diagram showing conventional coil switching method   The figure which shows the front end circuit of the conventional typical vehicle-mounted AM broadcast receiver   Diagram showing the characteristics of a typical conventional antenna stage   Diagram showing the basic principle of a variable virtual inductor   The figure which shows the equivalent circuit schematic of the circuit of FIG.   The figure which shows the resonance circuit which consists of variable type virtual inductor and antenna capacity and cable capacity   The figure which shows the equivalent circuit schematic of the circuit of FIG.   The figure which shows the circuit which frequency-controls the antenna stage tuning circuit and the RF stage tuning circuit with the voltage of the PLL synthesizer   The figure which shows the Example of the preamplifier and postamplifier of a virtual inductor   The figure which shows the Example of the local signal generator using a virtual inductor   The figure which shows the Example of the broadcast receiver by invention of Claim 1 and 2

Claims (2)

  A preamplifier before and after the high-pass filter consisting of a variable-capacitance diode and a first resistor has a voltage gain of less than +1 and as close as possible to +1, a sufficiently high input impedance, and a sufficiently low output impedance, and A post-amplifier is connected, and the input terminal of the pre-amplifier and the output terminal of the post-amplifier are connected by a second resistor to form a variable inductance type virtual inductor, and the virtual inductor and the antenna capacity and the cable capacity or those A frequency variable type resonance circuit is configured by a capacitor including the antenna stage tuning circuit of the receiver, and the antenna stage tuning circuit is supplied from a PLL synthesizer together with an RF stage tuning circuit including a coil and a variable capacitance diode. A broadcast receiver characterized in that the frequency is controlled by the same voltage.   A preamplifier before and after the high-pass filter consisting of a variable-capacitance diode and a first resistor has a voltage gain of less than +1 and as close as possible to +1, a sufficiently high input impedance, and a sufficiently low output impedance, and A post-amplifier is connected, and the input terminal of the pre-amplifier and the output terminal of the post-amplifier are connected by a second resistor to form a variable inductance type virtual inductor, and the frequency variable type resonance circuit is composed of the virtual inductor and the capacitor. To be a local signal generator of the receiver, and the local signal generator is frequency-controlled by the same voltage supplied from the PLL synthesizer together with an RF stage tuning circuit composed of a coil and a variable capacitance diode. Broadcast receiver characterized by.

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