JP5001980B2 - Antenna booster unit for terrestrial digital TV - Google Patents

Description

  The present invention relates to an antenna booster unit for terrestrial digital television.

  In television broadcasting, terrestrial digital broadcasting has started in the UHF band, and it has already been decided that the current analog terrestrial broadcasting will stop in July 2011. In the past, wide area broadcasting was mainly assigned to the VHF band, so the number of UHF channels that can be received in the same area was not so large, but since terrestrial digital broadcasting started Wide-area broadcasting is also incorporated into the UHF band, and the frequency usage of the UHF band is becoming overcrowded unprecedented. Along with this, the problem of reception disturbance due to adjacent channel waves and the same channel waves becomes serious especially when receiving low-power regional broadcast channels and distant radio wave broadcasts (hereinafter collectively referred to as weak electric field broadcasts). ing.

  In order to improve the reception quality C / N (carrier signal-to-noise ratio) of weak electric field broadcasting, it is effective to amplify the antenna signal with a booster and input it to a television receiver (for example, Patent Document 1). On the other hand, in terrestrial digital television broadcasting, an Orthogonal Frequency Division Multiplexing (OFDM) system is adopted. The OFDM scheme is one of multicarrier transmission schemes in which information is distributed and transmitted over a large number of subcarriers (subcarriers) whose center frequencies are orthogonal to each other, and has the advantage of reducing the effects of multipath distortion. The spectrum of the multicarrier modulation signal is represented as a superposed spectrum of a number of subcarriers. In the OFDM scheme, since each subcarrier is orthogonal to each other as described above, in principle, it should not affect other subcarriers. However, in reality, there is a problem of reception failure due to the effect of third-order intermodulation distortion. Is generated. Therefore, Patent Document 2 includes a terrestrial digital television broadcast band which has a GaAs-HEMT as a unit active element as a booster and has a saturation output of 15 dBm or more and is a reception target. The proposal which solves this problem is made | formed by employ | adopting the wideband amplifier which has a flat gain characteristic in the broadcast frequency band of 470 MHz or more and 770 MHz or less.

  At first glance, it seems to be a conventional means to increase the saturation output of the amplifier in order to prevent distortion at high received power. However, it is the high reception power channel itself that is distorted with output saturation that lowers the reception quality degradation by raising the saturation level of the amplifier output. Can't explain. In order to prevent such misunderstandings, the third-order intermodulation distortion does not occur as a distortion of the desired reception channel wave itself, but is caused by the distortion of another channel wave of a strong electric field having a different frequency. It is necessary to understand that it is positioned as a kind of interference wave (interference wave).

  As shown in FIG. 24, when the input / output characteristics of the amplifying unit are viewed, the waveform of the output signal may be corrupted with respect to the input signal due to the nonlinearity. Specifically, if it is caught in a non-linear part somewhere between the zero point and the peak point of the sine wave, the waveform will be distorted. The distortion in the state of being present is referred to as third-order distortion. The distorted waveform includes a fundamental frequency multiplication frequency component called a harmonic component, as can be easily understood by mathematically Fourier transforming. In a booster through which a plurality of signals having different frequencies pass, a sum or difference component of the harmonic component and the fundamental component is generated to disturb the main signal. For example, when two radio waves with different frequencies enter the amplifier, an interference wave derived from this sum or difference component is output from a frequency that should not be output, and a weak electric field channel to be received is located in that frequency band. The interference wave becomes noise, resulting in a decrease in reception quality.

  FIG. 25 shows an image in which interference waves that are not originally received are generated in adjacent 14ch and 17ch when broadcast waves are received in 15ch and 16ch. This is called third-order intermodulation distortion, and the substance is a harmonic interference wave generated by nonlinear distortion of another channel wave different from the desired channel wave. Here, it does not mean the distortion of the digital regional broadcast channel wave) itself. In other words, although third-order intermodulation distortion is named “distortion”, it should be noted that it does not deform the signal waveform of the desired received wave, but acts as interference wave noise that embeds the signal. .

  Digital terrestrial broadcast waves use OFDM, a system that sends about 5617 radio waves in a single channel, so intermodulation occurs in the broadcast waves, resulting in a situation where radio waves are disrupted in a chain reaction. Yes. FIG. 26 shows the spectrum of a multicarrier modulation signal of a channel with terrestrial digital television broadcasting. Although the superposition waveform of the fundamental frequency signal of each subcarrier is generated within the channel band, the superposition waveform of the third-order intermodulation distortion due to an arbitrary pair of 5617 subcarriers included in the channel is noted. It can be seen that not only the existing channel band but also the band of the adjacent channel protrudes, which affects the reception quality. In particular, when a regional broadcasting channel for low power transmission is adjacent to a wide-area digital broadcasting channel for high-power transmission, the carrier signal of the regional broadcasting channel whose reception level is low from the beginning, the high-order tertiary of the wide-area digital broadcasting channel is used. As a result of the overlapping of the intermodulation distortion components, the video quality degradation of the regional broadcast channel becomes very serious.

  In the case of analog broadcasting, the influence of interference waves due to third-order intermodulation distortion can occur between adjacent channels, but the effect is that the color balance of the video is slightly deteriorated or the image is roughened. The reception quality was not deteriorated so much as to be impossible. Therefore, even if the third-order intermodulation distortion (interference wave) is not actively suppressed, or if it is intended to reduce it, a countermeasure has been taken in the form of lowering the gain of the amplifier. The reason is that it is theoretically known that the output level of the interference wave due to third-order intermodulation distortion increases at a rate of twice when the input level increases. This is because, in the case of broadcasting, it has been improved to the extent that it can be sufficiently viewed only by adjusting the gain of the amplification section.

  However, in the terrestrial digital television broadcasting, the deterioration of the C / N ratio level of the regional broadcast channel due to the third-order intermodulation distortion interference wave is larger than expected, and the above-described amplification unit gain control cannot be dealt with at all. The reason is that since the video information is sent as digital bit data, unlike the analog video, the reception quality C / N ratio is below a certain limit value (specifically, 20 dB) even if the interference wave level is relatively low. This is because the video state suddenly deteriorates due to an increase in block noise, and viewing becomes impossible immediately. Therefore, terrestrial digital television is widely used because the third-order intermodulation distortion interference wave at the time of high reception power has a dramatic effect that directly affects whether or not the television image is received. Therefore, increasing the saturation output of the amplifying unit as a solution is not widely recognized as a “conventional means” in the field of terrestrial digital television.

JP 2007-36631 A Japanese Patent No. 4257369 JP 2008-5422 A

  As a result of further examination by the inventor, the problem relating to the viewing disturbance of the weak electric field channel of the terrestrial digital television broadcasting such as the regional broadcasting cannot be solved sufficiently only by increasing the saturation output of the amplification unit. It has been found. In particular, when booster output is distributed to multiple receivers at home, etc., fading (variation of reception level due to attenuation of radio waves due to weather etc. and multiple reflection of surroundings (mountains / buildings, etc.) When the influence of (attenuation) is significant, a viewing disturbance is likely to occur when receiving a low-power transmission broadcast or a distant weak radio broadcast.

  An object of the present invention is to receive local digital broadcasts with relatively low transmission power or out-of-service digital broadcasts even in a reception environment in which booster output is distributed to a plurality of receivers or in a reception environment where fading is likely to occur. An object of the present invention is to provide an antenna booster unit for terrestrial digital television that can greatly improve the reception quality during remote reception or the like.

Means for Solving the Problems and Effects of the Invention

The present invention solves the above-mentioned problems in an antenna booster unit for amplifying an antenna signal of terrestrial digital television broadcasting whose transmission frequency band is 470 MHz or more and 710 MHz or less and inputting the amplified signal to the front end side of the receiving device. To do
An amplifying unit having a high-frequency amplifying element using a GaAs-HEMT as an active element having a saturation output of 15 dBm or more and a minimum noise figure of 1.5 dB or less in a broadcast frequency band;
A DC bias supply circuit for supplying a DC bias voltage to the amplifying unit;
An input matching circuit that forms a booster input terminal by being inserted in series on the input side of the amplifying unit and is also used as a passive filter circuit having a pass band including a broadcast frequency band, and omits the input matching circuit In the input impedance characteristics of the amplification unit alone, the impedance point group on the Smith chart that minimizes the noise figure NF at each frequency in the broadcast frequency band is used as a reference noise minimizing impedance point, and the input matching circuit is provided. When the impedance point group on the Smith chart where the noise figure NF is minimized at each frequency in the broadcast frequency band is the actual noise minimizing impedance point, The magnitude of the reflection coefficient vector for the noise minimizing impedance point is the reference noise minimizing impedance. And having an an input matching circuit circuit constants are set reactance element becomes smaller as filtering circuitry than the magnitude of the reflection coefficient vectors for the point.

  By ensuring that the saturation output of the amplifying unit is 15 dBm or more, the linear region of the booster output is expanded, and from the amplified output spectrum of the multi-carrier modulation signal of each channel of the terrestrial digital television broadcast adopting the OFDM system, The influence of non-linear distortion (particularly third-order intermodulation distortion) generated in an individual channel or in a form protruding to an adjacent channel band can be dramatically reduced, which contributes to improvement in reception quality. In particular, when a regional broadcast channel whose transmission power level is lower than that of the wide-area broadcast channel sequence is set adjacent to the wide-area broadcast channel sequence, the low reception level of the regional digital broadcast is determined by the high electric field reception level derived from the wide-area digital broadcast. Of the non-linear distortion excited in the channel, and also the non-linear distortion (particularly, third-order intermodulation distortion) extending from the high power broadcast channel group to the low power transmission broadcast channel can be effectively avoided.

  In a medium strong electric field digital broadcast reception environment where the total power of the antenna reception output is -28 dBm or more due to the reception of the strong electric field digital broadcast (about 70 dBuV per wave is, for example, 8 waves) By using the one secured at 15 dBm or more, it is possible to secure a margin of 7-10 dB or more with respect to 20 dB as the reception limit for the reception quality C / N upon reception of a weak electric field digital television broadcast channel (for example, about 45 dBuV). As a result, the video quality of the regional broadcast channel can be sufficiently secured.

  If the saturation output of the high-frequency amplification element used in the amplification unit is less than 15 dBm, the influence of the above-described nonlinear distortion on the weak electric field broadcast channel in the terrestrial digital television broadcast band cannot be sufficiently reduced. In addition, there is no restriction | limiting in particular in the upper limit of the saturation output of a high frequency amplification element, For example, it is fully possible to about 25 dBm. The saturated output can be defined as output power P1 dB (1 dB Compressed Output Power) when compressed by 1 dB from the linearity in which the relationship of the output power to the input power is determined by the power gain.

  On the other hand, the amplifying unit incorporated in the booster amplifies noise together with the received signal from the antenna. Therefore, if a high-frequency amplification element with a high noise figure is used, noise generated by itself is superimposed on the input antenna signal and amplified together. Therefore, even if the gain of the amplification element itself is increased unnecessarily, the output signal It is not possible to improve the C / N ratio.

In the case of a terrestrial digital television broadcast receiving system, the antenna signal is amplified by at least two or more stages of devices including an antenna booster and a receiving device until it is finally output by the receiving device. Become. In such a multi-stage amplification system, the gain G and noise figure F of each device are set in order from the device closer to the input side, G ₁ , G ₂ , G ₃ ,..., And F ₁ , F ₂ , F ₃ ,. When expressed, the total noise figure F _tot is
F _tot = F ₁ + (F ₂ −1) / G ₁
+ (F ₃ -1) / G ₁ · G ₂ + (F ₄ -1) / G ₁ · G ₂ · G ₃ + (1)
If the gain G ₁ of the first stage device is sufficiently large, the noise figure F _{tot of the} entire system is almost determined by the noise figure F ₁ of the first stage device. In other words, no matter how much the gain and noise figure of the second and subsequent devices are improved, if the noise figure F1 of the _first stage device is high, the C / N of the final output signal is not improved.

  The antenna booster that is the subject of the present invention corresponds to the above-mentioned first stage device in the terrestrial digital television broadcast reception system, and since the amplification gain for the antenna signal is also large, its noise figure level eventually becomes that of the entire reception system. The noise figure will be determined. Therefore, the use of a high frequency amplifying element having a minimum noise figure of 1.5 dB or less directly contributes to an improvement in reception quality C / N of terrestrial digital television broadcasting. In other words, the noise figure of the booster itself has been reduced even for weak electric field broadcasts that often have to be received in the vicinity of the limit C / N, which suddenly becomes impossible to receive due to block noise or the like. The reception margin for the limit C / N can be greatly expanded. As a result, even when the booster output is distributed to multiple receivers, or even in an environment where fading is likely to occur due to the influence of the weather or mountains / buildings etc., weak electric field broadcasting is reliably received with high quality. It becomes possible.

  However, since an antenna and an antenna cable (coaxial cable) are always connected to a TV booster, signal reflection at both ends of the booster becomes a problem. In order to increase the booster output of broadcast reception signals, generally, a technique is used in which the impedance of the booster input / output end is matched with the input / output impedance of the amplifier in terms of power, and the characteristic impedance of the antenna or coaxial cable connected to the booster is taken. On the other hand, when the input / output impedance of the amplification unit alone is not power matched, an impedance matching circuit is inserted on the input / output side of the amplification unit. Thereby, the reflection loss at both ends of the amplifying unit is suppressed, and the level of the amplified signal output from the booster can be increased. However, as described above, the amplifying unit also amplifies the noise at the same time. Therefore, in order to improve the C / N of the booster output, it is desirable to suppress the amplified output level of the noise. In other words, with regard to noise suppression, that is, improvement (reduction) of the noise figure, the impedance (75Ω) at the booster input terminal is set to a minimum slightly apart from the maximum power matching impedance (a common complex impedance of S11) of the amplification element built in the booster. Gain close to the optimum power source impedance that gives the noise figure (reference noise minimization impedance: Γ′opt), that is, by deviating a predetermined amount from the gain maximization point (power matching: gain maximization impedance point Gamax) on the impedance, and gain Is that noise optimization (so-called noise matching) can minimize the noise level of the entire receiving system and improve the overall C / N while allowing a certain degree of reduction from the maximum point. means. As can be inferred from the above equation (1), this measure for improving the noise figure needs to be performed on the input side before the noise is amplified. In the present invention, the input matching circuit is specifically configured. This is done by optimizing the circuit constants.

  That is, in the present invention, the electric configuration of the booster is simplified by using the input matching circuit also as the passive filter circuit having the pass band including the broadcast frequency band. The inventor pays attention to the fact that the passive filter circuit always includes a reactance element (capacitor or inductor: an equivalent capacitance or equivalent reactance generated as a distributed constant circuit is also included as a concept), and the circuit of the reactance element. By optimizing the constant, the noise minimizing impedance point (actual noise minimizing impedance point Γopt) of the amplifying unit viewed from the booster input end formed in the input matching circuit is changed to the noise minimizing impedance point of the amplifying unit alone ( It has been found that the reference characteristic impedance point (generally Zi = 75Ω in the case of an antenna or coaxial cable frequently used in terrestrial digital broadcasting) can be approached rather than the reference noise minimizing impedance point Γ′opt). As a result, while maintaining impedance matching on the input side, the noise figure of the amplifying unit can be maintained at an optimum level, and it is possible to achieve both a noise figure level and a gain that are necessary and sufficient for receiving a weak electric field broadcast satisfactorily. .

  In Patent Document 3, an inductor is inserted as a reactance element between the source and ground of an FET that is an active element of an amplifier circuit, and a noise matching point for realizing low noise, and reflection with excellent reflection characteristics. A circuit configuration is disclosed in which an effect of bringing a matching point closer to each other is created and both low noise characteristics and reflection characteristics can be achieved. However, this method can achieve the desired effect in a higher frequency band (for example, SHF band adopted by BS broadcasting and CS broadcasting) than the UHF band adopted by terrestrial digital television broadcasting. The bandwidth that can be expected is narrow, and it is quite ineffective in the broadcasting frequency band of terrestrial digital television set widely in the UHF band. In fact, in Patent Document 3, due to the effect of the inductor connected to the source electrode of the FET, the stability of the low noise amplifier may deteriorate due to the fact that the source potential of the FET is not determined as a zero potential. Specifically, it is mentioned that the stability coefficient K is K <1 at high frequencies, and abnormal signal oscillation may occur when the low noise amplifier has gain at high frequencies. However, in the present invention, since the reactance element is inserted on the input end side of the high frequency amplifying element (that is, the gate side of the HEMT (FET) forming the active element), the above problem does not occur at all. The effect of achieving both a good noise figure and a necessary and sufficient gain level can be achieved in the entire broadcasting frequency band of terrestrial digital television broadcasting set in the UHF band.

  According to the high-frequency circuit simulation analysis conducted by the present inventor, the noise minimizing impedance point can be brought close to the reference characteristic impedance point by optimizing the circuit constant of the reactance element of the input matching circuit. The distribution (contour lines) of circles (equal noise figure circles) drawn on the Smith chart with the impedance point as the center and having a uniform noise figure (equal noise figure circle) also changes depending on the selection of circuit constants. At this time, when the value of the noise figure at the reference characteristic impedance point is N1 and the value of the noise figure at the noise minimizing impedance point is N0, the value of ΔN≡N1−N0 is 0.5 dB or less. It is more desirable to adjust the circuit constant of the reactance element of the input matching circuit in order to reduce the final noise figure at the booster output terminal. Furthermore, the noise figure level finally obtained at the booster output end is preferably 2.0 dB or less (preferably 1.5 dB or less; although there is no limit on the lower limit value, it is practically about 0.5 dB). .

  Also, the gain maximizing impedance point can be brought closer to the reference characteristic impedance point by optimizing the circuit constant of the reactance element of the input matching circuit. Thereby, the noise figure can be reduced and the amplification level of the antenna signal by the booster can be increased, which contributes to the improvement of the reception quality C / N. In this case, the amplification gain finally obtained at the booster output end is preferably 15 dB or more from the viewpoint of securing a necessary reception quality C / N level (specifically, 20 dB or more) for weak electric field broadcasting. .

  The input matching circuit can be configured as a high-pass filter circuit having a high-pass frequency band including a broadcast frequency band. In this case, an output circuit configured as a low-pass filter circuit that forms a booster output end and has a low-pass frequency band including a broadcast frequency band can be inserted in series on the output side of the amplifying unit. By dividing the upper and lower ends of the broadcast frequency band into a high-pass filter circuit (HPF) and a low-pass filter circuit (LPF) on the input side and output side of the amplification unit, the entire booster circuit can be broadcast. The steepness of frequency band cutout can be increased. By making the input matching circuit a high-pass filter circuit in which an inductor is inserted on the ground side, adjustment for making the noise minimizing impedance point approach the reference characteristic impedance point is facilitated.

  As described above, in the present invention, all the reactance elements for bringing the noise minimizing impedance point closer to the reference characteristic impedance point (75Ω) are connected to the input end side of the high frequency amplifying element. The ground terminal can be connected directly to the ground. As a result, there is no concern (such as abnormal signal oscillation) that the stability of the amplifier deteriorates due to the fact that the source potential of the FET (HEMT) is not determined as zero potential, as disclosed in Patent Document 3.

  Further, the high-pass filter circuit constituting the input matching circuit includes a series capacitor provided on the input signal transmission path connected to the input terminal of the high frequency amplifying element and two branches provided from the input signal transmission path to the ground side. A π-type HPF configured with a parallel inductor can also be configured to be used as a noise matching circuit. In this case, the noise matching circuit is adjusted so that the magnitude of the reflection coefficient vector for the actual noise minimizing impedance point is smaller than the magnitude of the reflection coefficient vector for the reference noise minimizing impedance point. Also, as an auxiliary element of the high-pass filter circuit that cooperates with the series capacitor and the parallel inductor, a series inductor provided on the input signal transmission path and a parallel capacitor provided by branching from the input signal transmission path to the ground side And can be provided. As a result, the degree of freedom of adjustment for optimizing the actual noise minimizing impedance point is increased, and the pass characteristics of the high-pass filter circuit forming the input matching circuit can be improved.

  In the case of a TV booster, it is desirable to take protective measures against a lightning surge for a high-frequency amplifying element forming an amplifying part because it is connected to an antenna installed outdoors. Among these, the booster input side to which the antenna is connected is likely to cause a surge pulse due to lightning induced to the antenna, but in the case of the booster of the present invention, the input matching circuit that also serves as a filter circuit is provided on the signal transmission line on the input side. Since the lightning surge pulse current can be discharged through the ground of the filter circuit, the high-frequency amplifying element can be protected relatively easily. For example, when the input matching circuit is configured as a high-pass filter circuit, a lightning surge pulse absorbing coil that branches from the input signal transmission path to the ground side is connected to the booster separately from the parallel inductor formed by the cored coil. It can be provided as an input side lightning surge protection circuit. By providing the lightning surge pulse absorbing coil on the ground side of the filter, the lightning surge pulse can be discharged to the ground side while absorbing the energy of the lightning surge, so that the protection effect on the input terminal side of the high frequency amplifying element is enhanced. In addition, the lightning surge pulse absorbing coil can function as a choke coil that prevents a high-frequency antenna signal from flowing to the ground side. The lightning surge pulse absorbing coil can be used in combination with one of the inductors constituting the π-type HPF described above. In addition, it is desirable to use an air-core coil so that it will not burn out even if a large current flows instantaneously due to a lightning strike (the impact current flowing through the absorption coil is an instantaneous value (several tens of microseconds)) A may be reached). The inductance is desirably set to 300 nH or less from the viewpoint of blocking the UHF signal from the ground and shorting a lightning surge frequency component of 1 MHz or less to the ground. Further, if the inductance of the lightning surge pulse absorbing coil is set within a range of ± 50% with respect to the inductance of the parallel inductor, the steepness of the lower band limit of the high-pass filter circuit can be increased.

  Next, the amplifying unit bypasses the output terminal and the input terminal of the high-frequency amplifying element with a feedback circuit that flattens the gain frequency characteristic of the high-frequency amplifying element so that the gain fluctuation in the broadcast frequency band is within 3 dB. It can be configured as an external connection. As a result, even if a weak electric field digital TV broadcast channel is received in any channel, the received signal can be uniformly amplified while reducing non-linear distortion, and reception quality can be greatly improved. Further, as a result of the feedback circuit being externally separated from the high-frequency amplification element, the thermal effect due to the feedback current is less likely to affect the amplification element, which is convenient for keeping the noise figure of the entire amplification unit low.

  The high frequency amplifying element can be configured as a positive single power amplifying element in which an enhancement type p-type GaAs-HEMT is used as an active element, a gate of the HEMT is assigned to an input terminal, a drain is assigned to an output terminal, and a source is assigned to a ground terminal. The DC bias supply circuit is configured to apply a DC bias voltage between the input terminal and the output terminal of the high-frequency amplification element. The high frequency amplifying element having the above-described configuration can achieve unipolarity of the bias power source by using a single enhancement type p-type GaAs-HEMT as an amplifying active element, and greatly simplifies and miniaturizes the circuit configuration. In addition, the low noise characteristic in the UHF band specific to GaAs-HEMT can be utilized to the maximum. In addition, since the feedback circuit is externally attached, the minimum noise figure inherent in the amplification element deteriorates due to the function of the internal negative feedback circuit (specifically, the input impedance of the amplification unit is affected by the impedance of the feedback circuit). Therefore, a low noise figure of 1.5 dB or less can be realized over the entire band of terrestrial digital television broadcasting.

  In the above configuration, the amplifying unit, the DC bias supply circuit, and the input matching circuit are mounted on the circuit board and connected to the first connector part connected to the booster input terminal of the circuit board and the booster output terminal. A booster housing having a second connector portion and accommodating a circuit board is provided, and the first connector portion is formed so as to be directly connectable to a coaxial cable connection socket on the antenna side, while the second connector portion is used to send an amplified signal to the receiving device. A coaxial cable for supply can be formed to be connectable.

A second terrestrial digital TV antenna booster unit according to the present invention amplifies a terrestrial digital TV broadcast antenna signal having a broadcast frequency band of 470 MHz or more and 710 MHz or less, and transmits the amplified signal to the front end side of the receiver. An antenna booster unit for input,
An enhancement type p-type GaAs-HEMT is used as an active element, and a positive single power supply amplifying element in which the gate of the HEMT is assigned to an input terminal, a drain is assigned to an output terminal, and a source is assigned to a ground terminal. A feedback circuit for flattening the gain frequency characteristic of the high frequency amplifying element in the broadcast frequency band is used as a high frequency amplifying element having a saturated output of 15 dBm or more and a noise figure of less than 1.5 dB. An amplifier connected externally in a form that bypasses the input terminal;
A DC bias supply circuit for applying and supplying a DC bias voltage between the input terminal and the output terminal of the high-frequency amplification element;
A circuit board on which an amplifier and a DC bias supply circuit are mounted;
The circuit board has a first connector portion connected to the booster input end and a second connector portion connected to the booster output end, and has a booster housing for accommodating the circuit board.

  In the above configuration, the reduction in the number of active elements and the number of peripheral circuit elements dramatically improves the environmental durability of the circuit while simultaneously reducing the size of the amplification unit. Even when used in an environment that is constantly exposed to direct sunlight and wind and rain, the necessary booster function can be maintained well over a long period of time.

  The feedback circuit is a distributed constant that branches from the input signal transmission path that connects the input matching circuit and the input terminal of the high-frequency amplification element, and that leads to the signal transmission path on the output end side of the high-frequency amplification element by bypassing the high-frequency amplification element It can be formed as having a feedback transmission path forming a line. On the feedback transmission path, the feedback factor determining DC resistance for determining the feedback factor of the feedback circuit and the reflection coefficient vector with respect to the actual noise minimizing impedance point so that the reflection coefficient ≤ 1/3. An adjustment capacitor having a capacitance of 1.5 pF or less that suppresses frequency fluctuations and a feedback rate compensation inductor having an inductance of 100 nH or less that compensates for frequency fluctuations of the feedback rate can be provided. By providing the above-mentioned adjustment capacitor on the feedback circuit, it is difficult to influence the impedance adjustment state of the input matching circuit that minimizes noise even though the feedback circuit is added. The noise figure can be kept low throughout. Further, by providing the feedback rate compensation inductor, it is possible to compensate for the frequency variation of the feedback rate due to the provision of the adjustment capacitor, and it is possible to keep the feedback rate within the optimum range over the entire broadcast frequency band.

  In addition, a stabilizing DC resistance that improves the amplification stability index of the amplifying unit on the high frequency side of the broadcast frequency band in a form that branches from the feedback transmission path to the ground side is provided in association with the DC resistance for determining the feedback rate. it can. This effectively suppresses an excessive increase in the output gain of the amplifier on the high frequency side of the broadcast frequency band, and the weak electric field channel set on the high frequency side of the broadcast frequency band also reduces nonlinear distortion. However, the received signal can be amplified uniformly, and the reception quality can be greatly improved. Also, a high-frequency gain suppression capacitor for suppressing a gain peak generated on the high frequency side of the broadcast frequency band in the gain frequency characteristics of the amplifying unit is provided in a form that branches from the output signal transmission path of the amplifying unit to the ground side. Alternatively, an attenuating DC resistor is provided on the output signal transmission path of the amplifying unit to suppress a gain peak that occurs on the high frequency side of the broadcasting frequency band in the gain frequency characteristic of the amplifying unit. It can be more effectively suppressed that the output gain of the amplifying section becomes too sensitive on the high frequency side.

  In the circuit board, an input matching circuit, an amplifying unit, and a DC bias supply circuit are mounted and mounted on the front surface side together with a transmission path for transmitting a UHF band reception signal, and a characteristic impedance of the transmission path is determined on the back surface side. A planar ground conductor (so-called solid ground) that reduces induction / radiation of noise superimposed on a received signal or a power supply can be configured. In this case, if the planar ground conductor is also formed in the mounting area of the feedback circuit on the back side of the circuit board, the feedback circuit pattern is capacitively coupled to the planar ground conductor, and the feedback operation is complicated by its parasitic impedance. There is a risk of becoming unstable or unstable. Therefore, it is desirable to omit the surface-type ground conductor on the back surface of the circuit board in the mounting area of the feedback circuit.

  As described above, the antenna booster unit for terrestrial digital television according to the present invention includes a circuit board on which an input matching circuit, an amplifying unit, and a DC bias supply circuit are mounted and connected to a booster input terminal of the circuit board. It has one connector part and a second connector part that is also connected to the booster output end, and has a booster housing that accommodates the circuit board. The first connector part is formed so as to be directly connectable to the coaxial cable connection socket on the antenna side. On the other hand, the second connector portion can be configured such that a coaxial cable for supplying an amplified signal to the receiving device can be connected. On the circuit board, the bias DC power supply input supplied via the coaxial cable signal transmission core wire is superimposed on the output of the amplified signal and branched from the signal transmission path on the booster output end side. A bias power supply line to be supplied to the supply circuit, and a power supply separation filter circuit for separating a high frequency signal forming an amplification signal from a bias DC power supply input on the bias power supply line are provided. In this case, the booster output side lightning surge protection circuit can be provided across the signal transmission path on the booster output end side and the bias power supply line.

The third of the antenna booster units for terrestrial digital television of the present invention amplifies the terrestrial digital television broadcast antenna signal having a broadcast frequency band of 470 MHz or more and 710 MHz or less, and transmits the amplified signal to the front end side of the receiver. An antenna booster unit for input,
In a broadcast frequency band, an amplifying unit including a high-frequency amplifying element in which a saturation output using GaAs-HEMT as an active element is secured to 15 dBm or more;
A DC bias supply circuit for supplying a DC bias voltage to the high-frequency amplifier,
A circuit board on which an amplifier and a DC bias supply circuit are mounted;
A first connector portion connected to the booster input end of the circuit board, a second connector portion similarly connected to the booster output end, and a booster housing for accommodating the circuit board,
The first connector part is formed so as to be directly connectable to a coaxial cable connection socket on the antenna side, while the second connector part is formed so that a coaxial cable for supplying an amplified signal to the receiving device can be connected,
On the circuit board, the bias DC power supply input supplied via the coaxial cable signal transmission core wire is superimposed on the output of the amplified signal and branched from the signal transmission path on the booster output end side. A power supply line for bias to be supplied to the supply circuit, and a power supply separation filter circuit for separating the DC power input for bias superimposed on the high frequency signal forming the amplification signal on the bias power line from the high frequency signal,
Furthermore, the booster output side lightning surge protection circuit is provided so as to extend over the signal transmission path on the booster output end side and the bias power supply line.

  The antenna booster unit having the above configuration can be used in-line with a coaxial cable outdoors. However, the coaxial cable is extended from an outdoor booster to an indoor receiver. In particular, when the antenna is directly connected to the booster housing, the outdoor cable length of the coaxial cable is particularly long.

Returning to the lightning surge problem described above once again, as described above, the surge pulse caused by the antenna-induced lightning to the booster input side can discharge the lightning surge pulse current via the ground of the input matching circuit that also functions as a filter circuit. In addition, since the surge energy itself of the antenna-induced lightning is relatively small, the protection measures are relatively easy. However, on the booster output side, more thorough surge protection measures are necessary for the reasons described below.
(1) Since the shield conductor covering the core wire of the coaxial cable extending from the booster output side is grounded on the receiver side, a high level electromagnetic field generated by direct lightning strikes to the long shield conductor. Since it returns to the ground through it, the surge energy is often much larger than that of antenna-induced lightning due to the long cable length (peak voltage ± 10 KV, pulse half-value width of several tens of us) Not a few).
(2) Normally, the booster output side has a structure in which the impedance to the ground side is increased so that the amplified high-frequency signal does not leak. As a result, when a strong surge pulse is received, almost no surge current can flow to the ground side, and if the DC bias supply circuit of the amplifying unit is provided on the substrate, the DC bias supply circuit passes through the DC bias supply circuit. Excessive instantaneous current flows through the high-frequency amplifying element, which tends to cause a problem of breaking the element.

  Therefore, if the booster output side lightning surge protection circuit is provided so as to extend over the signal transmission path on the booster output end side and the power supply line for bias, the above-described problems can be effectively solved.

  As mentioned above (2), the booster output side can hardly flow surge current to the ground side, so if the booster output side lightning surge protection circuit with the following structure linked with the bias power line is adopted, cable induction The high frequency amplifying element can be extremely effectively protected from a strong lightning surge pulse caused by lightning. First, the leakage from the signal transmission path on the booster output end side to the ground side is blocked between the signal transmission path and the ground, and the high frequency amplified signal on the signal transmission path is grounded. A surge protection element is provided for clamping the peak voltage of the lightning surge pulse applied from the signal transmission core wire to the booster output end side to a predetermined voltage. A surge smoothing choke coil for smoothing lightning surge pulses clamped by the surge protection element is provided on the bias power supply line. In other words, lightning surge pulses that arrive from the booster output side cable along the signal transmission path are clamped by a surge protection element that branches to the ground side, and a sharp and narrow half-value width input surge pulse is clipped by a peak voltage. It is converted into a pulse waveform (although it is a steep pulse with a narrow half-value width, for example, its peak value is cut off to 100 V or less). This surge protection element blocks the leakage of the high frequency amplified signal on the signal transmission path to the ground due to the equivalent capacitance. The surge pulse after the clipping process is further smoothed by the surge smoothing choke coil on the bias power line by this surge protection element, so that the instantaneous current level flowing to the high frequency amplifying element via the bias power line is reduced. It can be effectively reduced. The DC component generated by smoothing lightning surge pulses by the smoothing choke coil between the branch point of the bias power supply line and the output circuit on the signal transmission path on the booster output end side is sent to the amplifier side. Inserting a DC cut capacitor (for example, about 10 pF capacity: blocking leakage to the output side of the high frequency amplifying element on the signal transmission path) to prevent reverse flow, a high frequency amplifying element or an output circuit (chip component) Etc.) can be further enhanced.

The schematic diagram which shows the schematic structural example of the antenna booster unit for terrestrial digital television of this invention. The figure which shows the circuit structural example of the antenna booster unit of FIG. The disassembled perspective view which shows the structural example of a circuit board and a housing. The figure which shows the example of patterning of both surfaces of a circuit board in a component mounting state. The perspective view which shows an example of the attachment form to the UHF antenna of an antenna booster unit. FIG. 3 is an actual measurement diagram showing S parameter characteristics of the circuit of FIG. 2. The figure which shows the measurement example of the frequency characteristic of the gain and noise figure of the circuit of FIG. The figure which shows the equivalent circuit for simulation of the antenna booster unit of FIG. The figure which shows the simulation result of S parameter and NF characteristic of the circuit of FIG. The Smith chart (frequency: 600 MHz) which shows the input impedance characteristic in the single-piece | unit of the high frequency amplification element used for the circuit of FIG. FIG. 11 is a Smith chart (frequency: 600 MHz) shown with an unstable region superimposed on the input impedance characteristic of FIG. The Smith chart (frequency: 600 MHz) which shows the input impedance characteristic seen from the booster input end by the side of the input matching circuit of the high frequency amplification element used for the circuit of FIG. FIG. 13 is a Smith chart (frequency: 600 MHz) showing an unstable region superimposed on the input impedance characteristic of FIG. The Smith chart (frequency: 470 MHz) which shows the input impedance characteristic in the single-piece | unit of the high frequency amplification element used for the circuit of FIG. The Smith chart (frequency: 470 MHz) which similarly shows the input impedance characteristic seen from the booster input end by the side of the input matching circuit. The Smith chart (frequency: 700 MHz) which shows the input impedance characteristic in the single-piece | unit of the high frequency amplification element used for the circuit of FIG. The Smith chart (frequency: 700 MHz) which similarly shows the input impedance characteristic seen from the booster input end by the side of an input matching circuit. The figure which shows the simulation result which verifies the effect of the direct current | flow resistance for feedback rate determination accompanying the feedback circuit, and the high frequency gain suppression capacitor. The figure which shows the simulation result which verifies the effect of the capacitor for adjustment of a feedback circuit. The graph which shows the high temperature accelerated life test result done about the antenna booster unit of this invention. The model figure which shows an example which modeled the reception environment of the terrestrial digital television broadcasting in Tokyo area after the analog television broadcasting in the UHF band stopped. The figure which shows the result of the performance evaluation test of the antenna booster unit of this invention. Explanatory drawing of the effect of a booster output side lightning surge protection circuit. Explanatory drawing of the third order distortion. The figure explaining a mode that 3rd order intermodulation distortion behaves as an interference wave. The figure explaining the influence which the 3rd order intermodulation distortion has on the adjacent channel.

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing an example of an antenna booster unit for digital terrestrial television (hereinafter also simply referred to as a booster unit) according to the present invention. This antenna booster unit 1 amplifies an antenna signal of a terrestrial digital television broadcast received by the UHF antenna 200 and having a broadcast frequency band of 470 MHz or more and 710 MHz or less, and uses the amplified signal as a front end of the receiving device 40 (terrestrial digital tuner). For input on the side. The antenna booster unit 1 has a housing 13 in which a first connector portion 49 and a second connector portion 50 are formed, and is directly connected to the UHF antenna 200 by the first connector 50 and is connected to the second connector 49 via the cable connector 10A. A coaxial cable 10 is connected. The coaxial cable 10 is connected to a power supply unit 30 for supplying a power supply voltage to the antenna booster unit 1 by a cable connector 10 </ b> B, and a receiving device 40 is connected to the power supply unit 30. It is provided at the end of the DC output cable CDC of an AC adapter 3AD (of a well-known configuration in which a step-down transformer, a rectifier circuit, a smoothing capacitor, etc. are integrally molded) attached to a commercial AC power outlet that forms an external power source. The terminal PTM is attached to a DC power connector CON1 formed in the power supply unit 30.

FIG. 2 shows an example of the circuit configuration of the booster unit 1 shown in FIG. 1. The main parts thereof are an amplifying unit 2, an input matching circuit 3, an output circuit (output matching circuit) 4, a DC bias supply circuit 5 and a feedback. The circuit 6 is configured (in the drawing, circuit constant setting values are illustrated for each element, but the circuit constant setting values are not limited to this). The amplifying unit 2 has a high-frequency amplifying element IC1 having a saturation output of 15 dBm or more and a minimum noise figure of 1.5 dB or less and using GaAs-HEMT as an active element in a broadcast frequency band. DC cut capacitors C _i and C ₀ are arranged before and after that.

  The input matching circuit 3 is used in combination with a passive filter circuit having a passband including a broadcast frequency band while forming a booster input end Input by being inserted in series on the input side of the amplifying unit 2. Specifically, it is configured as a high-pass filter circuit having a high-pass frequency band including a broadcast frequency band. Further, the output matching circuit 4 is inserted in series on the output side of the amplifying unit 2 and forms a booster output terminal Output, and is configured as a low-pass filter circuit having a low-pass frequency band including a broadcast frequency band. Has been.

  Further, the amplifying unit 2 includes a feedback circuit 6 that flattens the gain frequency characteristic of the high frequency amplifying element IC1 so that the gain fluctuation in the broadcast frequency band is within 3 dB, and an output terminal Out1 and an input terminal of the high frequency amplifying element IC1. An external connection is made so as to bypass In1.

  The DC bias supply circuit 5 is for supplying a DC bias voltage to the amplifying unit 2, and specifically, applies a DC bias voltage between the input terminal In1 and the output terminal Out1 of the high frequency amplifier element IC1. .

Hereinafter, the configuration of each circuit will be described in more detail.
The high-frequency amplification element IC1 of the amplification unit 2 is composed of a positive single power supply amplification element (specifically, AE308 (manufactured by RFHIC)) using an enhancement type p-type GaAs-HEMT as an active element. The element is configured as a small outline transistor type package element in which the gate of the HEMT is assigned to the input terminal In1, the drain is assigned to the output terminal Out1, and the source is assigned to the ground terminal GND1. The single noise figure of the high frequency amplifying element IC1 in the 50 Hz to 800 Hz band is 0.4 to 0.5 dB as a standard value, and the gain is about 22 dB in the vicinity of 600 MHz, but the broadcast frequency band (470 MHz to 710 MHz) and has a gain frequency characteristic that monotonously decreases as the frequency increases (the gain decrease range at 470 MHz to 710 MHz is 8 to 10 dB). Further, the P1 dB value is secured at 20 dBm or more, and the tertiary output intercept point (IP3) is secured at 30 dBm or more. Note that the ground terminal GND1 of the high-frequency amplifying element IC1 is directly connected to the ground without passing through the ground additional impedance.

  Next, the high-pass filter circuit forming the input matching circuit 3 includes a series capacitor Ch provided on the input signal transmission path J1 connected to the input terminal In1 of the high-frequency amplifying element IC1, and a grounding side from the input signal transmission path J1. And a parallel inductor Lh2 provided in a branched manner. Further, another parallel inductor Lh1 is provided to be branched from the input end side of the series capacitor Ch, and is configured as a π-type high-pass filter (HPF) as a whole. Further, as an auxiliary element that cooperates with the series capacitor Ch and the parallel inductors Lh1 and Lh2, a series inductor Ls is provided on the input signal transmission path J1, and the input signal transmission path J1 branches to the ground side in parallel. A capacitor Cp is provided.

  FIG. 10 is a Smith chart showing the input impedance characteristics (frequency: 600 MHz) of the amplification unit 2 (high frequency amplification element IC) when the input matching circuit 3 is omitted. On the chart, an impedance point on the Smith chart that minimizes the noise figure NF is set as a reference noise minimized impedance point Γ′opt. On the other hand, FIG. 12 is a Smith chart showing the input impedance characteristic (frequency: 600 MHz) of the amplifying unit 2 viewed from the booster input terminal Input when the input matching circuit 3 is provided. On the chart, an impedance point group on the Smith chart where the noise figure NF is minimized at each frequency in the broadcast frequency band is defined as an actual noise minimized impedance point Γopt. Similarly, FIG. 14 (without the input matching circuit 3) and FIG. 15 (with the input matching circuit 3) have a frequency of 470 MHz, and FIG. 16 (without the input matching circuit 3) and FIG. 17 (with the input matching circuit 3) have a frequency of 700 MHz. The similar Smith chart is shown.

  As is apparent from these Smith charts, the actual noise minimizing impedance point Γopt when the input matching circuit 3 is inserted is the center of the Smith chart (booster unit) more than the reference noise minimizing impedance point Γ′opt at any frequency. Input / output characteristic impedance point: Zi = 75Ω). That is, the circuit constants of the reactance elements (inductors Lh1, Lh2, Ls and capacitors Ch, Cp) of the filtering circuit constituting the input matching circuit 3 are reflected coefficients with respect to the actual noise minimizing impedance point Γopt at each frequency in the broadcast frequency band. The magnitude of the vector is set to be smaller than the magnitude of the reflection coefficient vector with respect to the reference noise minimizing impedance point Γ′opt. Further, on each Smith chart, impedance points for maximizing the gain of the amplifying unit 2 (FIGS. 10, 14, and 16: reference gain maximizing impedance point Ga′max, and FIGS. 12, 15, and 17: actual gain maximizing impedance) Point Gamax) is also shown. It can be seen that at any frequency, the actual gain maximizing impedance point Gamax is closer to the center of the Smith chart than the reference gain maximizing impedance point Ga'max.

  10, 12, and 14 to 17, the distribution (contour lines) of circles (equal noise figure circles) drawn on the Smith chart with the noise minimizing impedance point as the center and having the same noise figure (equal noise figure circle) are also obtained. It can be seen that it varies depending on the selection of circuit constants. At this time, when the noise figure value at the center of the Smith chart is N1 and the noise figure value at the noise minimizing impedance point is N0, the value of ΔN≡N1-N0 is 0.5 dB or less. The circuit constants of the reactance elements of the input matching circuit 3 are adjusted.

  The input matching circuit 3 (high-pass filter circuit) includes an air-core coil that is branched from the input signal transmission path J1 to the ground side separately from the parallel inductor Lh2 formed of a cored coil. A lightning surge pulse absorbing coil Lh1 (inductance: 300 nH or less, 20 nH in this embodiment) is provided as a booster input side lightning surge protection circuit LS2. The lightning surge pulse absorbing coil Lh1 constitutes a π-type high-pass filter (HPF) together with the series capacitor Ch and the parallel inductor Lh2.

  Next, the feedback circuit 6 branches from the input signal transmission path J1 that connects the input matching circuit 3 and the input terminal In1 of the high-frequency amplification element IC1, and bypasses the high-frequency amplification element IC1. A feedback transmission path JF connected to the output end side signal transmission path J1 is provided. On the feedback transmission path JF, the magnitude of the reflection coefficient vector with respect to the feedback factor determining DC resistance Rf for determining the feedback factor of the feedback circuit 6 and the actual noise minimizing impedance point Γopt is reflection coefficient ≦ 1/3. As described above, the adjustment capacitors Cf and Ca for suppressing the frequency variation and the feedback rate compensation inductor La for compensating for the frequency variation of the feedback rate are provided.

  From the feedback transmission path JF, a stabilized DC resistance Rs that improves the amplification stability index of the amplifying unit 2 on the high frequency side of the broadcast frequency band in a form that branches to the ground side accompanies the feedback resistance determining DC resistance Rf. Is provided. Further, a high frequency gain suppression capacitor for suppressing a gain peak generated on the high frequency side of the broadcast frequency band in the gain frequency characteristic of the amplifying unit 2 in a form branched from the output signal transmission path J2 of the amplifying unit 2 to the ground side. Ct is provided. Furthermore, an attenuating DC resistor Xo is provided on the output signal transmission path J2 of the amplifying unit 2 to suppress a gain peak generated on the high frequency side of the broadcast frequency band in the gain frequency characteristic of the amplifying unit 2.

  Next, the low-pass filter circuit constituting the output matching circuit 4 has two series inductors Lp and Lo and parallel capacitors Cs and Cv. The series inductor Lp in the previous stage includes the Q of the inductor (coil). A DC resistor Rd for reducing the value is connected in parallel. Further, a parallel inductor Lc for reinforcing the steepness of the lower limit of the band of the high-pass filter circuit formed by the input matching circuit 3 is also provided.

  In the present embodiment, the output line of the amplified signal from the booster output terminal Output is also used as the bias power supply line PL of the amplifying unit 2. The bias power line PL is provided so as to be branched from the signal transmission path J3 on the booster output end Output side, and the bias DC power input is connected to the signal transmission core of the coaxial cable 10 so as to overlap the output of the amplified signal. And supplied to the DC bias supply circuit 5 via the bias power line PL. On the bias power supply line PL, a power supply separation filter circuit 5F1 (consisting of a parallel capacitor Cu and a series inductor Lu) for separating a high-frequency signal forming an amplified signal from a bias DC power supply input is provided. In the present embodiment, a high-frequency signal cutoff circuit 5F2 is provided for preventing a high-frequency signal from being fed back to the input terminal In1 of the amplifying unit 2 through the DC bias supply circuit 5 and degrading the stability of the circuit operation. ing. The high-frequency signal cutoff circuit 5F2 is configured as a π-type low-pass filter circuit including parallel capacitors C1 and C2 and a series inductor L.

  The power input from which the high-frequency signal has been removed is supplied to the DC bias supply circuit 5 via the regulator IC 2 for voltage stabilization. The DC bias supply circuit 5 is for applying a bias voltage between the input terminal In1 (gate) and the output terminal Out1 (drain) of the high frequency amplifying element IC1, and the main part is a DC resistor for setting the bias voltage. In addition to the groups R1 to R4, high-frequency cutoff parallel capacitors Cd, Cd2, Cg and choke coils Ld, Lg are appropriately inserted.

  A booster output side lightning surge protection circuit LS1 is provided across the signal transmission path J3 on the booster output end Output side and the bias power line PL. The booster output side lightning surge protection circuit LS1 has a surge protection element SA (in this embodiment, RHCA-900Q43u manufactured by Okaya Electric Industries Co., Ltd.) branched from the signal transmission path J3 on the booster output end Output side to the ground side. Is provided. The surge protection element SA blocks leakage of the high frequency amplified signal on the signal transmission path J3 to the ground side between the signal transmission path and the ground, and from the signal transmission core of the coaxial cable 10 to the booster output terminal Output. It serves to clamp the peak voltage of the lightning surge pulse applied to the side to a predetermined voltage. Further, a surge smoothing choke coil CH for smoothing lightning surge pulses clamped by the surge protection element SA is provided on the bias power supply line PL. Further, a direct current generated by smoothing lightning surge pulses by the smoothing choke coil CH is provided between the branch point of the bias power supply line PL and the output circuit 4 on the signal transmission path J3 on the booster output terminal Output side. A DC cut capacitor Cb for preventing the component from flowing back to the amplifying unit 2 side is inserted.

  As shown in FIG. 1, the antenna booster unit 1 is used in a form of being connected inline on a coaxial cable 10 that forms an antenna cable. Specifically, the input matching circuit 3, the amplifier 2, the output matching circuit 4, and the DC bias supply circuit 5 in FIG. 2 are mounted on the circuit board 70 in FIG. Further, the first connector portion 50 connected to the booster input end Input of the circuit board 70 and the second connector portion 49 similarly connected to the booster output end Output are provided, and the booster housing 13 that accommodates the circuit board 70 is provided. . The booster housing 13 is formed in a hollow cylindrical shape by a metal material (for example, brass or the like clad with stainless steel). As shown in FIG. 5, the first connector portion 50 is a female screw type (F type) connector. It is formed so that it can be directly connected to the coaxial cable connection socket 200T on the antenna 200 side (specifically, it can be screwed to the antenna output terminal 200T formed in the terminal box 200B of the UHF antenna 200). The second connector portion 49 is formed as a male screw type (F type) connector so that the coaxial cable 10 for supplying an amplified signal to the receiving device 40 can be connected. Specifically, the circuit board 70 is assembled to the cable connection base 42, and the male screw portion formed on the outer peripheral surface of the cable connection base 42 is inserted while the circuit board 70 is inserted into the cylindrical booster housing 13. The booster housing 13 is adapted to be screwed into a female screw portion formed on the inner peripheral surface of the opening. The first connector portion 49 is formed integrally with the cable connection base 42.

  FIG. 4 is an enlarged view of the circuit board 70. The circuit board 70 has a first main surface forming a surface as a component mounting surface for surface mounting the components of the circuits 2 to 6 (indicating the mounting position with the aid of the reference numerals in the circuit diagram of FIG. 1). The planar ground conductor GPB is formed on the second main surface forming the back surface. Each transmission path J is coupled with its ground plane conductor to form a microstrip line. The planar ground conductor GPB formed on the back side of the circuit board 70 has a structure in which the mounting corresponding region of the feedback circuit 6 is a notch PCV, and the planar ground conductor is omitted in the notch PCV. ing.

  FIG. 6 shows an actual measurement result of the S parameter characteristics of the booster unit. It can be seen that it has a flat gain characteristic (S21) in the broadcast frequency band of 470 MHz to 710 MHz, which is the broadcast reception band of terrestrial digital television. Further, the input reflection loss (S11) is also reduced to approximately 3 or less in terms of the voltage standing wave ratio in the reception band. FIG. 7 shows the frequency characteristics of the gain and noise figure. Regarding the gain, it has an extremely flat and good gain characteristic that falls within 20 to 22 dB in the broadcast reception band, and the noise figure is less than 1 dB in the broadcast reception band, in particular, the main broadcast occupation band of 13 ch to 33 ch. It can be seen that a very good value of 0.7 to 0.8 dB is obtained.

  FIG. 9 shows a simulation result of S parameter characteristics using commercially available software (high frequency / microwave EDA tool manufactured by MEL Co., Ltd .: S-NAP / Pro). The circuit constants of the respective components show individual values in the equivalent circuit diagram of FIG. 8 as input setting values for performing simulation. Note that an equivalent cavity resonator structure formed by inductive coupling with the cylindrical booster housing 13 is formed by forming a notch PCV in the planar ground conductor GPB on the back surface side of the circuit board 70. I am doing a simulation. It can be seen that both the gain (S21) and the noise figure (NF) substantially match the simulation results of FIG.

  For example, FIG. 21 schematically shows the reception environment of terrestrial digital TV broadcasting in the Tokyo area after the analog television broadcasting in the UHF band stopped in July 2011 (schematic level of strong electric field wide area digital broadcasting). An example is shown). The total number of received channel waves is 10. Of these, strong electric field digital broadcast channel groups (received radio wave intensity is 70 dBuV or more per wave: so-called wide-area broadcast), which is the main cause of generation of interfering harmonics due to third-order intermodulation distortion. Channel group) There are 8 waves, and weak electric field digital TV broadcast channel channel group (received radio wave intensity is less than 40 dBuV per wave: local broadcast channel or remote The prefectural broadcasting channel) has two waves. The total power of the antenna reception output becomes −28 dBm or more, and a so-called medium strong electric field digital broadcast reception environment is formed.

  According to the booster unit of the present embodiment, the high-frequency amplifying element IC1 having a saturation output of 15 dBm or more (20 dBm or more in the present embodiment) is used in the medium strong electric field digital broadcast reception environment as described above. As a result, the level of interference harmonics due to third-order intermodulation distortion is greatly reduced, and plays a major role in ensuring reception quality C / N particularly for weak electric field digital television broadcast channel channels.

  On the other hand, the amplifying unit 2 incorporated in the booster amplifies the noise together with the received signal from the antenna 200, but according to the booster unit of the present embodiment, by using the high frequency amplifying element IC1 having a noise figure of 1.5 dB or less. This directly contributes to the improvement of the reception quality C / N for the weak electric field digital television broadcast channel.

  In order to improve the C / N of the booster output, it is naturally desirable to suppress the noise amplification output level. In the booster unit of the present embodiment, the high frequency amplifying element IC1 having a particularly good noise figure characteristic as described above is adopted. However, the extremely low noise figure characteristic deteriorates due to the reflection characteristic on the booster input side as much as possible. As described above with reference to FIGS. 10 to 17, the impedance of the booster input terminal Input is set to a minimum noise slightly apart from the maximum power matching impedance of the amplifying element built in the booster (co-complex impedance of S11). The circuit constants of the reactance elements constituting the input matching circuit 3 are optimized so as to approach the optimum power source impedance point that gives an index, that is, the reference noise minimizing impedance point Γopt ′. That is, by optimizing the circuit constant of the input matching circuit 3, the impedance of the booster input end Input is intentionally offset by a predetermined amount from the reference gain maximizing impedance point (Ga'max), and the gain is allowed to be slightly reduced from the maximum point. However, the noise is optimized. As a result, the amplifying unit 2 can maintain the gain at a sufficient level, and can maintain the ultra-low noise figure characteristic inherent to the high-frequency amplifying element IC1, as shown in FIG. A sufficient noise figure level and gain necessary for good reception are achieved.

  Thus, according to the configuration of the antenna booster 1, the booster itself can be applied to weak electric field broadcasts that are often unable to be received due to block noise or the like and are often forced to receive in the vicinity of the limit C / N. As a result, the reception margin with respect to the limit C / N can be greatly expanded to about 7 to 10 dB, for example, even for weak electric field digital television broadcast channel channels. As a result, even when the booster output is distributed to multiple receivers, or even in an environment where fading is likely to occur due to the influence of the weather or mountains / buildings etc., weak electric field broadcasting is reliably received with high quality. It becomes possible.

  As is apparent from the circuit configuration of FIG. 2, a reactive element is inserted into the input terminal In1 of the high-frequency amplifying element IC1 (that is, the gate side of the HEMT (FET) that forms the active element). Compared with the configuration in which the inductor is connected to the source electrode of the FET, the source potential of the FET can be determined as a zero potential, which contributes to the stabilization of the operation of the amplification unit 2 in the broadcast frequency band. For example, as shown in FIG. 11, in the high frequency amplifier element IC1 alone, an unstable region where the stability coefficient K becomes 1 or less and the operation of the amplifying unit becomes unstable is applied to the Smith chart. May oscillate abnormally. However, by adding the input matching circuit 3 with optimized circuit constants, the unstable region is excluded from the Smith chart as shown in FIG. 13, and good in all broadcast frequency bands of terrestrial digital television broadcasting. Noise figure and stable gain characteristics are achieved.

  Although the high frequency amplifier element IC1 has a very low noise figure as a single unit, the gain fluctuates relatively greatly depending on the frequency. Therefore, the gain frequency characteristic of the amplifying unit 2 can be changed in the broadcast frequency band by adding the feedback circuit 6 externally. Is flattened to be within 3 dB. When the feedback circuit 6 is externally attached, the minimum noise figure inherent in the amplifying element deteriorates due to the function of the internal negative feedback circuit (specifically, the input impedance of the amplifying unit 2 is affected by the impedance of the feedback circuit 6). The problem that is greatly collapsed from Γopt of) is effectively solved.

  By providing the adjustment capacitors Cf and Ca, the feedback circuit 6 is less affected by the impedance adjustment state of the input matching circuit 3 where noise is minimized, even though the feedback circuit 6 is added. The noise figure can be kept low throughout the frequency band. Also, by providing this feedback rate compensation inductor La, it is possible to compensate for the frequency variation of the feedback rate due to the provision of the adjustment capacitors Cf and Ca, and the feedback rate is stably maintained over the entire broadcast frequency band. .

  Further, by providing the stabilized DC resistance Rs that branches from the feedback transmission path JF to the ground side in association with the DC resistance Rf for determining the feedback rate, the output gain of the amplifying unit 2 on the high frequency side of the broadcast frequency band is provided. Is effectively suppressed from becoming too sensitive. Further, the high-frequency gain suppression capacitor Ct is branched from the output signal transmission path J2 of the amplifying unit 2 to the ground side, and the attenuating DC resistor Xo on the output signal transmission path J2 of the amplifying unit 2 is further provided. In the high frequency side of the broadcast frequency band, the output gain of the amplifying unit 2 is suppressed from becoming excessively high. FIG. 18 is a simulation result performed to verify the effect of adding the stabilized DC resistance Rs. When the high-frequency gain suppression capacitor Ct and the stabilized DC resistance Rs are omitted in the circuit of FIG. As shown on the left, a sharp gain peak associated with self-oscillation occurs on the high frequency side, whereas by inserting a high-frequency gain suppression capacitor Ct and a stabilizing DC resistance Rs of a predetermined value, It can be seen that oscillation is suppressed and the above gain peak disappears.

  Further, the left side of FIG. 19 shows a simulation result when the values of the adjustment capacitors Cf and Ca are optimized, and the right side shows a simulation result when the value is slightly deviated from the appropriate point. When the values of the adjustment capacitors Cf and Ca deviate from the appropriate points, it can be seen that the value of the noise figure NF slightly increases over the entire broadcast frequency band.

  The amplifying unit 2 uses a single enhancement type p-type GaAs-HEMT as an amplifying active element as the high-frequency amplifying element IC1, and a feedback circuit 6 is also externally attached. Compared to a case where an IC with a high degree of integration is employed. The physical durability has been dramatically improved. As a result, as shown in FIG. 5, the booster output can be maintained well over a long period of time even when used in an environment where it is directly connected to the outdoor antenna 200 and exposed to direct sunlight and wind and rain. it can. FIG. 20 shows the results of an accelerated life test conducted to confirm this effect (measured with N number = 4). That is, the booster unit 1 configured as shown in FIG. 3 is placed in a constant temperature bath to keep the inside of the bath at 90 ° C., and a signal generator is connected to the input side to input a simulated broadcast signal, while the output side is It was connected to a heat-resistant coaxial cable, and the signal output level was measured continuously for 4 days and nights with a spectrum analyzer. In either case, it can be seen that the output is hardly degraded. It should be noted that the acceleration test conditions for the case where the booster unit 1 is used at room temperature (35 ° C.) are estimated to have an acceleration coefficient of 2347 times from the Arrhenius equation. It is thought that it corresponds to about 25 years.

  As shown in FIG. 5, when using the booster unit 1 connected to the antenna 200 outdoors, it is desirable to take protective measures against lightning surges on the high-frequency amplifier element IC <b> 1 forming the amplifier unit 2. Among these, the surge pulse due to the antenna-induced lightning to the booster input side can be discharged as a lightning surge pulse current through the ground of the input matching circuit 3 that also serves as a filter circuit, and the surge energy of the antenna-induced lightning itself is also reduced. Since it is relatively small, it is dealt with by a lightning surge pulse absorbing coil Lh1 made of an air-core coil. On the other hand, on the booster output side, as shown in FIG. 1, in the coaxial cable 10 extending long from the booster output end, it is easy to receive induced lightning to the shield conductor covering the core wire, and the surge energy is increased by the longer cable length. It becomes considerably large. As is clear from the circuit configuration of FIG. 2, the booster output side has a structure in which the impedance to the ground side is increased so that the amplified high-frequency signal does not leak, so that it receives a strong surge pulse. In this case, almost no surge current can flow to the ground side, and an excessive impact current flows to the high-frequency amplifying element IC1 via the DC bias supply circuit 5, which tends to break the element.

  In this embodiment, the lightning surge pulse that arrives from the booster output side cable along the signal transmission path is clamped by the surge protection element SA (FIG. 2) that branches to the ground side, and as shown in FIG. An input surge pulse LSP having a narrow half-value width is converted into a clipped pulse waveform CSP having a peak voltage of 100 V or less. Then, the surge pulse CSP after the clipping process by the surge protection element SA is further smoothed by the surge smoothing choke coil CH (FIG. 2) on the bias power line PL (FIG. 23: waveform BS), and for bias It is possible to effectively reduce the instantaneous current level flowing through the high-frequency amplifier element IC1 through the power line PL.

  A reception test for evaluating the performance of the booster unit 1 was performed as follows. The survey reception locations were the Shonai River Bank (weather: heavy rain) and Mizuho Ward (near Mizuho Athletic Stadium, weather: clear) in Nishi-ku, Nagoya, Aichi Prefecture. In any region, the terrestrial digital broadcast channel can receive U13, U18, U19, U20, U21, U22 as a wide-area broadcast channel and U23 as a regional broadcast channel. Two regional broadcast channels, Mie Broadcasting (U27) and NHK Tsu Broadcasting (U28), are transmitted across Ise Bay as far-weak broadcast channels.

  The configuration of the receiving system used for the measurement is as shown in FIG. 1, and the output of the booster unit 1 (example) is a commercially available receiving device (terrestrial digital TV tuner: Panasonic Corporation, TU-MHD500), The signal level meter (LF985: manufactured by Reader Electronics Co., Ltd.) was switched and input, and the reception state, reception level, and reception C / N ratio of each channel were measured. In the measurement under concentrated rain, an attenuator (attenuation rate: 12 dB) is used to assume the case where the booster unit 1 is directly connected to a receiving device or a signal level meter and the reception situation distributed to a plurality of receiving devices. And connected in the same way.

  For comparison, the same measurement was performed when two types of commercially available boosters (Comparative Example 1 and Comparative Example 2) were connected instead of the booster unit of the example. As the characteristics of each booster, the gain, noise figure (NF), rated output, 1 dB saturation output, third-order intercept point IP3, and maximum input level value per wave at which third-order intermodulation distortion IM3 is 60 dBc are shown in Table 1. It is summarized in.

  FIG. 22 collectively shows the obtained measurement results. First, on the Shonai River bank, the reception strength of U28 is relatively high at about 32 dBuV, but the reception strength of U27 is very weak at about 26 dBuV. Under the condition where no attenuator is provided in this receiving environment (that is, when the amplified output is not distributed to a plurality of receiving apparatuses), the booster of Comparative Example 1 having a low gain and the booster of Comparative Example 2 having a high noise figure NF are implemented. With the booster of Example 1, the reception quality C / N exceeded the reception limit value of 20 dB, and no reception failure such as block noise was observed. However, when an attenuator was provided, the boosters of Comparative Example 1 and Comparative Example 2 both had a reception quality C / N of less than 20 dB, and reception failure due to block noise was observed. On the other hand, although the booster of the example is a concentrated rain environment where fading is likely to occur, even when an attenuator is provided, the reception quality C / N exceeds 20 dB and the broadcast can be received satisfactorily.

  On the other hand, at Mizuho Stadium, the reception intensity of U28 is about 25 dBuV, which is extremely weak compared to the case of the Shonai River bank. Under this environment, under the condition that no attenuator is provided, each booster of Comparative Example 1 and Comparative Example 2 has a reception quality C / N of less than 20 dB, and the booster of Comparative Example 1 having a particularly low gain cannot be received at all. It became a state. Further, although the booster of Comparative Example 2 was able to receive an image, a reception failure due to block noise was observed. However, the booster of the example was able to receive broadcasts satisfactorily because the reception quality C / N exceeded 20 dB despite such a weak reception wave.

1 Antenna Booster Unit for Digital Terrestrial Television 2 Amplification Part IC1 High Frequency Amplifying Element 3 Input Matching Circuit 4 Output Matching Circuit (Output Circuit)
5 DC bias supply circuit 5F1 power supply separation filter 6 feedback circuit Input booster input terminal Output booster output terminal LS1 booster output side lightning surge protection circuit LS2 booster input side lightning surge protection circuit 13 booster housing 49 first connector part 50 second connector part 70 Circuit board

Claims (16)

An antenna booster unit for amplifying an antenna signal of a terrestrial digital television broadcast having a broadcast frequency band of 470 MHz or more and 710 MHz or less, and inputting the amplified signal to the front end side of the receiving device,
In the broadcast frequency band, an amplifying unit having a high-frequency amplifying element using GaAs-HEMT as an active element, having a saturated output of 15 dBm or more and a minimum noise figure of 1.5 dB or less;
A DC bias supply circuit for supplying a DC bias voltage to the amplifier;
Booster input formed by being serially inserted into the input side of the amplifying portion, while being also used as a passive filter circuit having a passband encompassing the broadcasting frequency band, the amplification viewed from the front Symbol booster input The noise minimizing impedance point, which is the impedance point group on the Smith chart at which the noise figure NF is minimized at each frequency in the broadcast frequency band , is used as the reference characteristic impedance point that is the center of the Smith chart. let closer, and, when the value of the noise figure in the reference characteristic impedance point N1, the value of N0 noise figure of the previous Kizatsu sound minimize impedance point, or less than a predetermined value the value of .DELTA.N = N1-N0 An input matching circuit to be
A feedback circuit externally connected so as to bypass an output terminal and an input terminal of the high frequency amplifying element, and flattening a gain frequency characteristic of the high frequency amplifying element that fluctuates in the broadcast frequency band, the input matching A distributed constant line that branches from the input signal transmission path connecting the circuit and the input terminal of the high-frequency amplifying element and connects to the signal transmission path on the output end side of the high-frequency amplifying element is formed by bypassing the high-frequency amplifying element A feedback transmission path is provided, and on the feedback transmission path, a feedback factor determining DC resistor for determining a feedback factor of the feedback circuit and an increase in a noise figure of the high frequency amplifying element due to the provision of the feedback circuit are suppressed. And an adjustment capacitor for compensating the frequency variation of the feedback rate due to the provision of the adjustment capacitor. Terrestrial digital television antenna booster unit characterized by having and circuitry. The input matching circuit is configured as a high-pass filter circuit having a high-pass frequency band including the broadcast frequency band,
An output circuit is provided which is inserted in series on the output side of the amplification unit and forms a booster output end, and is configured as a low-pass filter circuit having a low-pass frequency band including the broadcast frequency band. The antenna booster unit for terrestrial digital television according to claim 1. The ground terminal of the high frequency amplifying element is directly connected to the ground without going through the ground additional impedance ,
The high-pass filter circuit forming the entering-force matching circuit,
A π-type HPF composed of a series capacitor provided on an input signal transmission path connected to the input terminal of the high-frequency amplification element, and two parallel inductors provided by branching from the input signal transmission path to the ground side ;
As an auxiliary element of the high-pass filter circuit that cooperates with the series capacitor and the parallel inductor, the series inductor provided on the input signal transmission path,
3. The antenna booster unit for terrestrial digital television according to claim 2 , further comprising: a parallel capacitor that is branched from the input signal transmission path to the ground side.   In the high-pass filter circuit, a lightning surge pulse absorbing coil comprising an air-core coil that is branched from the input signal transmission path to the ground side separately from the parallel inductor constituted by a cored coil 4. The antenna booster unit for terrestrial digital television according to claim 3, wherein the booster input side lightning surge protection circuit is provided.   The antenna booster unit for terrestrial digital television according to claim 4, wherein an inductance of the lightning surge pulse absorbing coil is set to 300 nH or less.   The ground according to any one of claims 1 to 5, wherein the feedback circuit flattens the gain fluctuation of the high-frequency amplifier having a gain fluctuation in the broadcast frequency band larger than 3 dB within 3 dB. Antenna booster unit for wave digital TV. The high frequency amplifying element is a positive single power amplifying element in which an enhancement type p-type GaAs-HEMT is used as an active element, a gate of the HEMT is assigned to the input terminal, a drain is assigned to the output terminal, and a source is assigned to a ground terminal. Configured,
7. The antenna booster unit for terrestrial digital television according to claim 6, wherein the DC bias supply circuit applies the DC bias voltage between the input terminal and the output terminal of the high-frequency amplifier element. A circuit board on which the amplifier, the DC bias supply circuit, and the input matching circuit are mounted;
A first connector portion connected to the booster input end of the circuit board, and a second connector portion similarly connected to the booster output end, and a booster housing for accommodating the circuit board,
The first connector portion is formed to be directly connectable to a coaxial cable connection socket on the antenna side, while the second connector portion is formed to be connectable to a coaxial cable for supplying the amplified signal to the receiving device. The antenna booster unit for terrestrial digital television according to claim 7.   The terrestrial digital television antenna according to any one of claims 1 to 8, wherein the adjustment capacitor of the feedback circuit has a capacitance of 1.5 pF or less, and the feedback rate compensation inductor has an inductance of 100 nH or less. Booster unit.   A stabilizing DC resistor for improving the amplification stability index of the amplifying unit on the high frequency side of the broadcast frequency band is provided in association with the feedback resistance determining DC resistor so as to branch from the feedback transmission path to the ground side. The antenna booster unit for terrestrial digital television according to any one of claims 1 to 9.   A high-frequency gain suppression capacitor is provided to suppress a gain peak generated on the high frequency side of the broadcast frequency band in the gain frequency characteristic of the amplifying unit in a form branched from the output signal transmission path of the amplifying unit to the ground side. The antenna booster unit for terrestrial digital television according to any one of claims 1 to 10.   12. The attenuating DC resistor for suppressing a gain peak generated on the high frequency side of the broadcast frequency band in the gain frequency characteristic of the amplifying unit is provided on the output signal transmission path of the amplifying unit. Antenna booster unit for terrestrial digital TV.   The input matching circuit, the amplifying unit, and the DC bias supply circuit are mounted and mounted on the front surface side together with a transmission path for transmitting a UHF band received signal, and a characteristic impedance of the transmission path is determined on the back surface side. A circuit board on which a planar ground conductor for reducing induction / radiation of noise superimposed on the received signal and power supply is formed, and the planar grounding in the mounting area of the feedback circuit on the back surface of the circuit board The antenna booster unit for terrestrial digital television according to any one of claims 1 to 12, wherein a conductor is omitted. A circuit board on which the input matching circuit, the amplifier, and the DC bias supply circuit are mounted;
A first connector portion connected to the booster input end of the circuit board, a second connector portion similarly connected to the booster output end, and a booster housing for accommodating the circuit board,
The first connector part is formed to be directly connectable to a coaxial cable connection socket on the antenna side, while the second connector part is formed to be connectable to a coaxial cable for supplying the amplified signal to the receiving device,
On the circuit board, a DC power source for bias supplied via the signal transmission core of the coaxial cable in a manner to be superimposed on the output of the amplified signal is branched from the signal transmission path on the booster output end side. A bias power supply line for supplying the DC bias supply circuit in a form, and a power supply separation filter circuit for separating the high frequency signal forming the amplified signal from the bias DC power supply input on the bias power supply line,
14. The ground according to claim 1, further comprising a booster output side lightning surge protection circuit extending across the signal transmission path on the booster output end side and the bias power supply line. Antenna booster unit for wave digital TV.   The booster output-side lightning surge protection circuit is provided so as to branch from the signal transmission path on the booster output end side to the ground side, and the high-frequency amplified signal on the signal transmission path is between the signal transmission path and the ground. A surge protection element that blocks leakage to the ground side and clamps a peak voltage of a lightning surge pulse applied to the booster output end side from the signal transmission core of the coaxial cable to a predetermined voltage; and 15. The antenna booster unit for terrestrial digital television according to claim 14, further comprising a surge smoothing choke coil that is provided on the bias power supply line and smoothes a lightning surge pulse clamped by the surge protection element. A DC component generated by smoothing the lightning surge pulse by the smoothing choke coil between the branch point of the bias power supply line and the output circuit on the signal transmission path on the booster output end side 16. The antenna booster unit for terrestrial digital television according to claim 15, wherein a DC cut capacitor for preventing backflow to the amplifying unit side is inserted.