JPH10322169A - Television signal receiving tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a circuit Q which is made almost constant across the entire reception frequency band, therefore, an input synchronization circuit in which band width the transmission loss in synchronous characteristic can be made constant, and to make it difficult to receive a disturbance signal, and to improve NF(noise factor). SOLUTION: This tuner is provided with an input terminal 3, a first varactor diode 8, a second varactor diode 16, and an input synchronizing circuit 9 in which synchronizing frequencies are changed according to the change of the capacitance value of the second varactor diode 16. In this case, the input synchronization circuit 9 is connected via the first varactor diode 8 with the input terminal 3, and the capacitance value of the first varactor diode 8 is changed in the same direction as the direction of the change in the capacitance value of the second varactor diode 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal receiving tuner used for a television receiver, a VTR (Video Recorder) or the like, and more particularly to a UHF in a television signal receiving tuner. The present invention relates to an input circuit section of a tuner section.

[0002]

2. Description of the Related Art A conventional television signal receiving tuner (hereinafter simply referred to as a tuner) will be described with reference to FIGS. First, FIG. 6 shows a circuit of a conventional tuner. In FIG. 6, a VHF tuner unit 21 for receiving a VHF band television signal and a UHF tuner unit 22 for receiving a UHF band television signal,
It is connected to the input terminal 23. VHF tuner 21
Is the intermediate frequency trap circuit 24, the VHF input tuning circuit 2
5, a VHF high-frequency amplifier 26, etc.
The F tuner section 22 includes a coupling capacitor 27, a UHF input tuning circuit 28, a UHF high frequency amplifier 29, and the like. The UHF input tuning circuit 28 further includes an impedance conversion circuit 30 and a main tuning circuit 31. The impedance conversion circuit 30 includes two inductors 32 and 33 connected in series with each other. The main tuning circuit 31 includes a main inductor 34 and a varactor diode 35 connected in parallel to the main inductor 34. It is constituted by.

A coupling capacitor 27 has a capacitance of several pF (picofarads), is connected between an input terminal 23 and a connection point between inductors 32 and 33 connected in series, and is input to the input terminal 23. VHF band television signal is greatly attenuated among the
UH without significantly attenuating F-band television signals
Send to F input tuning circuit 28. And the coupling capacitor 2
7, the impedance on the signal source side as viewed from the input terminal 23 side is two inductors 32, 33 connected in series with each other.
Is increased by the inductance ratio. The main tuning circuit 31 is connected in parallel to the series-connected inductors 32 and 33, applies a tuning voltage from a tuning voltage terminal 36 to a varactor diode 35, and adjusts the tuning frequency of the UHF input tuning circuit 28. Can be changed.

In the VHF tuner section 21, first, an intermediate frequency trap circuit 24 removes an interference signal in an intermediate frequency band, and then a VHF input tuning circuit 25.
To select a desired VHF band television signal,
The signal is amplified by the HF high-frequency amplifier 26. The frequency is converted to an intermediate frequency signal by a mixer (not shown) of the VHF tuner 21. On the other hand, in the UHF tuner section 22, the UHF band television signal input via the coupling capacitor 27 changes the capacitance of the varactor diode 35 to a desired channel in the UHF input tuning circuit 28. Is selected and amplified by the UHF high-frequency amplifier 29. The frequency is converted to an intermediate frequency signal by a mixer (not shown) of the UHF tuner section 21.

Here, an antenna (not shown) is connected to the input terminal 23. The impedance of the antenna is usually a pure resistance of 75Ω, where r is the signal source side including the coupling capacitor 27. The impedance Z1 is Z1 =
It is represented by r-jx1. When this impedance Z1 is converted into a parallel circuit, as shown in FIG.
r + x12 / r and a reactance component X1 = −j (x1
+ R2 / x1), of which the resistance component R1
Is the inductor 3 of the impedance conversion circuit 30 of FIG.
The value is converted into a large value by 2 and 33, and is connected in parallel to the UHF input tuning circuit 28. here,
x1 is the reactance of the coupling capacitor 27. Assuming that the capacitance value of the coupling capacitor 27 is C1, x1 = 1 / ω
It is represented by C1.

The resistance component R1 comprises a frequency-independent resistance r and a frequency-dependent resistance component x12 / r, and the resistance component x12 / r includes a coupling capacitor 27.
Is included, and the reactance x1
Is inversely proportional to the frequency because the capacitance value of the coupling capacitor is constant. Therefore, the resistance component R1 is
As shown in FIG. 8, the frequency increases as the frequency decreases, and decreases as the frequency increases.

Therefore, the bandwidth B1 in the tuning characteristics of the UHF input tuning circuit 28 becomes wider as the tuning frequency becomes higher, and becomes narrower as the tuning frequency becomes lower, as shown in FIG. Therefore, the circuit Q increases as the tuning frequency decreases, and the circuit Q decreases as the tuning frequency increases.
Becomes smaller. Therefore, the insertion loss of the UHF input tuning circuit 28 increases as the tuning frequency decreases. FIG. 10 shows this state. When the tuning frequency is low (f1), the bandwidth b1 is narrow, and when the tuning frequency is high (f3), the bandwidth b3 is wide. In addition, the insertion loss L1 when the tuning frequency is low is larger than the insertion loss L3 when the tuning frequency is high. The frequency (f) at which the tuning frequency is intermediate between f1 and f3
The bandwidth and the insertion loss in 2) are b2 and L2, respectively.
Where the bandwidth (b1) when the tuning frequency is low, the transmission loss (L1) and the bandwidth (b1) when the tuning frequency is high
3) and an insertion loss (L3).

[0008]

As described above, the tuning characteristic of the UHF input tuning circuit 28 in a conventional television signal receiving tuner is such that as the receiving frequency becomes lower,
As Q increases and the bandwidth decreases, the transmission loss increases, and conversely, as the reception frequency increases, Q
Are smaller and the bandwidth is wider. For this reason, when the reception frequency is low, there is an advantage that it is difficult to receive an interfering signal, but there is a problem that NF (noise figure) is deteriorated. Conversely, when the reception frequency is high, NF is improved. There is a problem that the NF is easily received, and it is difficult to balance the NF with the difficulty in receiving the interference signal. Therefore, the television signal receiving tuner of the present invention realizes an input tuning circuit which has a substantially constant circuit Q over the entire receiving frequency band, and therefore has a substantially constant bandwidth and transmission loss in tuning characteristics. It is intended to make it difficult to receive an interference signal and to improve NF.

[0009]

In order to solve the above problems, a television signal receiving tuner according to the present invention has an input terminal, a first varactor diode, and a second varactor diode. With the second varactor diode
An input tuning circuit for changing a tuning frequency according to a change in the capacitance value of the first varactor diode. The input tuning circuit is coupled to the input terminal via the first varactor diode. Is changed in the same direction as the change direction of the capacitance value of the second varactor diode.

A television signal receiving tuner of the present invention is a television signal receiving tuner for receiving a VHF band television signal.
A tuner section for receiving a television signal in the UHF band;
The first varactor diode is provided in an HF tuner section, and the first varactor diode is a high-pass filter that attenuates the VHF band television signal and passes the UHF band television signal.

In the television signal receiving tuner of the present invention, the same tuning voltage is applied to the first varactor diode and the second varactor diode.

Further, the television signal receiving tuner of the present invention comprises a first inductor and a second inductor connected in series with each other, which constitute the input tuning circuit together with the second varactor diode. One end of the first varactor diode is connected to a connection point between the first inductor and the second inductor.

Further, in the television signal receiving tuner of the present invention, one end of the first inductor is grounded, and the VHF band television is formed by the first varactor diode and the first inductor. A trap circuit for attenuating the signal was constructed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A television signal receiving tuner according to the present invention (hereinafter simply referred to as a tuner) will be described with reference to FIGS. FIG. 1 shows a tuner circuit according to the present invention. In FIG. 1, a VHF tuner 1 for receiving a television signal in the VHF band and a UHF tuner 2 for receiving a television signal in the UHF band are connected to an input terminal 3. The VHF tuner 1 comprises an intermediate frequency trap circuit 4, a VHF input tuning circuit 5, a VHF high frequency amplifier 6, etc., while the UHF tuner 2 comprises
It comprises a DC blocking capacitor 7, a first varactor diode 8 as a coupling capacitor, a UHF input tuning circuit 9, a UHF high frequency amplifier 10, and the like.

The UHF input tuning circuit 9 further includes an impedance conversion circuit 11 and a main tuning circuit 12 connected in parallel to the impedance conversion circuit 11. The impedance conversion circuit 11 includes a first inductor 13 and a second inductor 14 connected in series with each other, and one end of the first inductor 13 is grounded. The main tuning circuit 12 includes a main inductor 15 and a second varactor diode 16 connected in parallel to the main inductor 15 and serving as a tuning capacitor. One end of the second inductor 14 forming the impedance conversion circuit 11 is connected to one end of the main inductor 15 forming the main tuning circuit 12 and the second varactor diode 1.
6, the impedance conversion circuit 11 and the main tuning circuit 12 are connected in parallel to form a UHF input tuning circuit 9. In addition,
A capacitor 17 connected in series to the other end of the main inductor 15 and a second end of the second varactor diode 16 (cascade).
The capacitor 18 connected between the ground and the ground is for blocking DC.

The first varactor diode 8 relatively attenuates the VHF band television signal among the television signals input to the input terminal 3, and does not attenuate the UHF band television signal very much. UHF input tuning circuit 9
It has the function of a high-pass filter for sending to One end (cathode) of the first varactor diode 8 is connected to the input terminal 3 via the DC blocking capacitor 7, and the other end (anode) is connected to the first inductor 13 connected in series.
And the second inductor 14.
Therefore, this first varactor diode 8 couples the UHF input tuning circuit 9 to the input terminal 3. A common tuning voltage is applied to the respective cathodes of the first varactor diode 8 and the second varactor diode 16 from the tuning voltage terminal 19, and the respective capacitances are changed by the change of the tuning voltage. The value increases and decreases in the same direction and changes. The change range of the capacitance value between the first varactor diode 8 and the second varactor diode 16 is as follows.
It is approximately several pF (picofarad) to ten and several pF.

The impedance conversion circuit 11 composed of the first inductor 13 and the second inductor 14 has an impedance on the signal source side when the input terminal 3 is viewed from the first varactor diode 8 which is a coupling capacitor. -Step up the dance and convert it greatly, and connect the impedance-converted impedance of the signal source side to the UHF input tuning circuit 9 in parallel. Therefore, the UHF input tuning circuit 9
It has a function of matching the impedance on the signal source side with the input impedance of the UHF high-frequency amplifier 10 connected to the next stage of the UHF input tuning circuit 9.

In the VHF tuner 1,
First, after removing an interfering signal in the intermediate frequency band by the intermediate frequency trap circuit 4, a desired VHF band television signal is selected by the VHF input tuning circuit 5 and amplified by the VHF high frequency amplifier 6. The frequency is converted to an intermediate frequency signal by a mixer (not shown) connected to the VHF tuner section 1 after the VHF high frequency amplifier 6. On the other hand, U
In the HF tuner section 2, a DC blocking capacitor 7,
UHF input via the first varactor diode 8
The television signal of the band is the second varactor diode 1
6, the desired UHF band television signal is selected by the UHF input tuning circuit 9,
It is amplified by the HF high-frequency amplifier 10. The frequency is converted into an intermediate frequency signal by a mixer (not shown) connected to the UHF tuner section 2 at a stage subsequent to the UHF amplifier 10.

Here, an antenna (not shown) is connected to the input terminal 3. The impedance of the antenna is usually a pure resistance of 75Ω, where r is the first varactor diode which is a coupling capacitor. The impedance Z2 on the signal source side including the mode 8 is expressed by Z2 = r-jx2. When this impedance Z2 is converted into a parallel circuit, as shown in FIG. 2, a resistance component R2 = r + x22 / r and a reactance component X2 =-(x2 + r2 / x2) are obtained.
The resistance component R2 is converted into a large value by the impedance conversion circuit 11 in FIG. 1 and is connected in parallel to the UHF input tuning circuit 9. Where x
Reference numeral 2 denotes the reactance of the first varactor diode 8, and when the capacitance value of the first varactor diode 8 is C2, it is represented by x2 = 1 / ωC2.

The resistance component R2 is composed of a frequency-independent resistance r and a frequency-dependent resistance component x22 / r. The frequency-dependent resistance component x22 / r has a first varactor diode 8 connected thereto. The reactance x2 is inversely proportional to the frequency, but the capacitance C2 of the first varactor diode 8 changes so as to decrease as the frequency increases, so that the frequency-dependent resistance component x22 / r is as shown by curve a in FIG. 3, and its slope is lower than that of curve b which shows the frequency-dependent resistance component x12 / r (see FIG. 8) of the conventional resistance component R1. Becomes gentler in the low frequency region, and larger in the high frequency region.

The resistance R2 is equal to the first inductor 13 and the second inductor 14 of the impedance conversion circuit 11.
Therefore, the signal is multiplied by (1 + L2 / L1) 2 and connected in parallel to the UHF input tuning circuit 9. Here, L1
Is the inductance of the first inductor 13, and L
2 is the inductance of the second inductor 14. The bandwidth B2 of the tuning characteristic of the UHF input tuning circuit 9
Is as shown in curve C of FIG.
1 (see FIG. 9), the slope is gentler than that of the curve d, and in a low frequency region (for example, f1), the bandwidth b4 is wider than the conventional bandwidth b1, and a high frequency region (for example, f1). For example, in f3), the bandwidth b6 can be narrower than the conventional bandwidth b3. Also, the bandwidth b5 at the intermediate frequency (for example, at f2) can be substantially the same as the conventional bandwidth b2.

Correspondingly, as the tuning frequency becomes lower, the insertion loss of the UHF input tuning circuit 9 is set to values L4, L5 and L6 which are almost the same as the insertion loss L2 at the intermediate frequency f2 regardless of the frequency. Can be.

The first varactor diode 8, which is a coupling capacitor, is also used as a high-pass filter.
Since a trap circuit can be formed by the first inductor 13 of the impedance conversion circuit 11 in the UHF input tuning circuit 9, the series resonance frequency of the first varactor diode 8 and the first inductor 13 is set in the VHF band. If the frequency is set to, the television signal in the VHF band can be greatly attenuated. In addition, since the trap frequency changes according to the frequency of the received UHF band television signal, the VHF band television signal can be efficiently attenuated.

As described above, the television signal receiving tuner of the present invention uses the first varactor diode 8 for the coupling capacitance,
Since the tunable capacitance of the HF input tuning circuit 9 is changed in the same direction as the increase / decrease direction of the second varactor diode 16, the bandwidth of the UHF input tuning circuit 9 is wider at low frequencies than in the prior art. At higher frequencies, the bandwidth can be narrower than before. Therefore, the insertion loss of the UHF input tuning circuit 9 can be reduced at a low frequency as compared with the related art. Therefore, both the bandwidth and the insertion loss can be equalized over the entire frequency, and as a result, NF at low frequencies can be improved, and interference signals can be hardly affected even at high frequencies.

In the television signal receiving tuner of the present invention, the first varactor diode 8 is used as a coupling capacitor, and the first varactor diode 8 is connected to a UHF
In addition to the high-pass filter that passes the television signal in the band, the frequency is changed so as to be small, so that the cutoff frequency changes in accordance with the frequency in the UHF band to be received, and the television in the VHF band is changed. The John signal can be greatly attenuated.

[0025]

As described above, the television signal receiving tuner according to the present invention has an input terminal, a first varactor diode, a second varactor diode and the second varactor diode. An input tuning circuit for changing a tuning frequency according to a change in the capacitance value of the diode; coupling the input tuning circuit to the input terminal via the first varactor diode; The capacitance value of the input tuning circuit is changed in the same direction as the change direction of the capacitance value of the second varactor diode. The frequency can be narrower than before. Therefore,
The insertion loss of the tuning circuit can be reduced at a low frequency. Therefore, both the bandwidth and the insertion loss can be equalized over the entire frequency, and as a result, NF at low frequencies can be improved, and interference signals can be hardly affected even at high frequencies.

A television signal receiving tuner according to the present invention is a VHF receiving television signal in a VHF band.
A tuner section for receiving a television signal in the UHF band;
The first varactor diode is provided in the HF tuner section, and the first varactor diode is a high-pass filter that attenuates the VHF band television signal and passes the UHF band television signal. , The cutoff frequency changes corresponding to the frequency, and the television signal in the VHF band can be greatly attenuated.

Further, in the television signal receiving tuner of the present invention, since the same tuning voltage is applied to the first varactor diode and the second varactor diode, the tuning voltage is used as it is. Thus, the capacitance value of the first varactor diode as the coupling capacitance can be easily changed.

A television signal receiving tuner according to the present invention includes a first inductor and a second inductor connected in series with each other, which constitute the input tuning circuit together with the second varactor diode. Since one end of the first varactor diode is connected to a connection point between the first inductor and the second inductor, the impedance of the signal source can be freely set by the first and second inductors. And can be connected to a tuning circuit, whereby the bandwidth of the tuning circuit, the circuit Q and therefore the insertion loss can be set appropriately.

Further, in the television signal receiving tuner of the present invention, one end of the first inductor is grounded, and the VHF band television is formed by the first varactor diode and the first inductor. Since the trap circuit for attenuating the signal is configured, if the series resonance frequency of the second varactor diode and the first inductor is set to the frequency in the VHF band, the television signal in the VHF band can be greatly attenuated. I can do it. In addition, since the trap frequency changes according to the frequency of the received UHF band television signal, the VHF band television signal can be efficiently attenuated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a television tuner of the present invention.

FIG. 2 is an equivalent circuit of the impedance on the signal source side when viewing the input terminal side from the coupling capacitance in the television tuner of the present invention.

FIG. 3 is a frequency characteristic diagram of a resistance of an impedance on a signal source side when viewing an input terminal side from a coupling capacitance in the television tuner of the present invention.

FIG. 4 is a frequency characteristic diagram of a tuning characteristic bandwidth in a UHF tuning circuit of the television tuner of the present invention.

FIG. 5 shows UHF in the television tuner of the present invention.
FIG. 4 is a tuning characteristic diagram of the tuning circuit.

FIG. 6 is a circuit diagram of a conventional television tuner.

FIG. 7 is an equivalent circuit of the impedance on the signal source side when viewing the input terminal side from the coupling capacitance in a conventional television tuner.

FIG. 8 is a frequency characteristic diagram of the resistance of the impedance of the signal source side when viewing the input terminal side from the coupling capacitance in the conventional television tuner.

FIG. 9 is a frequency characteristic diagram of a bandwidth of a tuning characteristic in a UHF tuning circuit of a conventional television tuner.

FIG. 10 shows UHF in a conventional television tuner.
FIG. 4 is a tuning characteristic diagram of the tuning circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 VHF tuner part 2 UHF tuner part 3 Input terminal 4 Intermediate frequency trap circuit 5 VHF input tuning circuit 6 VHF high frequency amplifier 7, 17, 18 DC blocking capacitor 8 Second varactor diode 9 UHF input tuning circuit Reference Signs List 10 UHF high frequency amplifier 11 Impedance conversion circuit 12 Main tuning circuit 13 First inductor 14 Second inductor 15 Main inductor 16 Second varactor diode 19 Tuning voltage terminal R2 Resistance component X2 Reactance component

Claims (5)

[Claims] An input tuning circuit having an input terminal, a first varactor diode, and a second varactor diode, wherein a tuning frequency changes according to a change in a capacitance value of the second varactor diode. The input tuning circuit is coupled to the input terminal via the first varactor diode, and the capacitance value of the first varactor diode is changed to the capacitance of the second varactor diode. A television signal receiving tuner characterized in that the value is changed in the same direction as the change direction. 2. A UHF tuner for receiving a VHF band television signal, and a UHF tuner for receiving a UHF band television signal, wherein the input tuning circuit is connected to the UHF tuner. 2. The apparatus according to claim 1, wherein the first varactor diode is a high-pass filter that attenuates the VHF band television signal and passes the UHF band television signal. Television signal receiving tuner. 3. The television signal receiving tuner according to claim 1, wherein the same tuning voltage is applied to said first varactor diode and said second varactor diode. . 4. A first inductor and a second inductor, which are connected in series with each other and constitute the input tuning circuit together with the second varactor diode, are connected to one end of the first varactor diode. 4. The television signal receiving tuner according to claim 1, wherein the television signal receiving tuner is connected to a connection point between the first inductor and the second inductor. 5. An end of the first inductor is grounded,
5. A television signal receiving tuner according to claim 4, wherein said first varactor diode and said first inductor constitute a trap circuit for attenuating said VHF band television signal.