JPH0114727B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronically tuned tuner, in which automatic gain control circuit characteristics (AGC characteristics) of a high frequency amplification stage are improved by connecting a coaxial resonator and a variable capacitance diode in a predetermined arrangement. It is an object of the present invention to provide an electronic tuning tuner that can be improved.

FIG. 1 shows a specific circuit diagram of an example of a conventional electronic tuning tuner. In the figure, 1 is the case of the electronic tuning tuner, which is at ground potential, 2 is the received signal input terminal, 3 is the tuning voltage V t input terminal, and 4 is the tuning voltage V _t input terminal.
is the AGC voltage input terminal, and 5 is the power supply voltage +B input terminal. A high frequency television signal in the UHF band, for example, which enters the input terminal 2 is supplied to the coaxial resonator 6 and is induced in the coaxial resonator 7 from this, and the inductance value of the coaxial resonator 7 and the capacitance of the variable capacitance diode 8 are Only a high frequency television signal equal to a tuning frequency determined by a value etc. is applied to the first gate of an N-channel quadrupole MOS field effect transistor (FET) _Q1 for high frequency amplification.

The high frequency television signal applied to the first gate is transmitted through the coaxial resonator 11 connected to the drain of FET Q ₁ , the variable capacitance diode 12, and the coaxial resonator 1.
After being selectively tuned by a tuning circuit consisting of 3 to 16 and a variable capacitance diode 17, the coaxial resonator 18
is induced by the current and is supplied to the emitter of the mixing NPN transistor _Q2 . Here, the coaxial resonators 9, 1
0 and 15 are used as inductance elements for adjusting characteristic impedance.

On the other hand, an NPN transistor Q ₃ and a coaxial resonator 20 connected in series between the base of Q ₃ and the ground
The variable capacitance diode 21 and the like constitute a local oscillator, and the local oscillation frequency taken out from the base side of _Q3 is supplied to the emitter of transistor _Q2 , where it is mixed with the selectively tuned high-frequency television signal. After frequency conversion, a constant _intermediate frequency signal (IF
signals). This intermediate frequency signal passes through a parallel circuit consisting of a coil 23, a resistor 24, and a capacitor 25 in series, removes unnecessary components, and is outputted from an output terminal 26.

Therefore, the tuning voltage V _t entering the input terminal 3
differs for each reception channel, and the tuning voltage V _t of the desired channel is set by the variable capacitance diodes 8, 12, 1.
It is well known that selective tuning is performed by applying reverse bias voltages to channels 7 and 21 and varying their capacitances to vary the tuning frequency to that of a desired channel. Also, input terminal 4
The AGC voltage is applied to the gain control gate of FET _Q1 .

In the above-mentioned conventional electronically tuned tuner, if the received high-frequency television signal entering the input terminal 2 flows into the coaxial resonator 6 in the direction of the arrow at a certain moment, then the signal induced in the coaxial resonator 7 at this time is The signal flows in the direction of arrow _S0 , and the amplified signal current of the input high frequency television signal flows in the direction of arrow _S1 through the drain of FET _Q1 . In addition, there is a reverse transfer capacitance (feedback capacitance) Crss between the gate and drain of FET Q ₁ .
Therefore, the high frequency television signal that enters the first gate flows directly to the drain in the direction of arrow _S2 , which is the opposite direction to _S1 .

At the same time, the high frequency television signal induced in the coaxial resonator 7 is directly induced in the coaxial resonator 11 and flows as a signal current in the direction of arrow _S3 , which is the opposite direction to _S0 . There is a shield plate between coaxial resonators 7 and 11, but the shield is not complete and there is a gap between it and the case. A high frequency television signal is induced into 11. In this way, when a signal current flows in the coaxial resonator 7 in the direction of arrow S ₀ , the drain side of FET Q ₁
Signal currents flow in the directions S ₁ , S ₂ , and S ₃ . However, among these signal currents, the signals flowing in the directions of S ₂ and S ₃ become unnecessary signals.

In other words, the above conventional electronic tuning tuner
The AGC voltage vs. gain attenuation characteristic (AGC characteristic) is the second
As shown in the figure, when the cut-off point approaches 1V, the signal current S ₁ becomes extremely small, and the signal current S ₂
and S ₃ to a value approximately equal to the sum of
The gain of FET Q ₁ suddenly decreases and reaches the maximum gain attenuation as shown in the figure. Then, when the AGC voltage becomes 1V or less, the signal current _S1 becomes 0. On the other hand, a signal current equal to the sum of signal currents S ₂ and S ₃ flows through the coaxial resonator 11, and conversely, the gain increases slightly. For this reason, the amount of gain attenuation peaks downward near the above-mentioned cutoff point as shown in FIG.
This downward peak (so-called bounce of the AGC characteristic) is around 10 dB to 20 dB around 1.5 V, which sometimes caused malfunctions in AGC operation.
Also, if the received UHF television broadcast band changes from channel 14 to channel 83, both
Since the difference in AGC characteristics is large as shown in Figure 2,
The disadvantage was that the image disturbance ratio when the gain was attenuated was about 10 dB lower than when the gain was at maximum.

The present invention eliminates the above-mentioned drawbacks,
Each embodiment will be described below with reference to FIGS. 3 to 7.

FIG. 3 shows the first electronic tuning tuner according to the present invention.
A specific circuit diagram of an example is shown. In the figure, the same parts as in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. The present invention focuses on the fact that the above disadvantages occur when the unnecessary signal currents S ₂ and S ₃ flow in the same direction, and so that the unnecessary signal currents S ₂ and S ₃ flow in opposite directions. Coaxial resonators 7, 11, 1 of each tuned circuit on the input side and output side of FET Q ₁ for high frequency amplification
6 and variable capacitance diodes 8, 12, and 17 are changed in connection arrangement.

In the first embodiment, as shown in Fig. 3, the connection arrangement of the double-tuned circuit on the output side of FET Q ₁ is changed,
The drain of FET Q ₁ is coil 27, capacitor 2
8 are connected in series to the connection point of the coaxial resonator 11 and the capacitor 29, and the terminal of the coaxial resonator 11 opposite to the connection terminal with the capacitor 29 is connected to the cathode of the variable capacitance diode 12'. has been done. This variable capacitance diode 12'
The anode of the variable capacitance diode 17' is connected to the anode of the variable capacitance diode 17', and these anodes are grounded. The cathode 17' is connected to one end of the coaxial resonator 16.

Therefore, the coaxial resonator 7 is affected by the UHF band high frequency television signal that has just entered the input terminal 2.
When a signal current flows in the direction of the arrow shown by S ₀ in Figure 3, the amplified signal current flows to the drain of FET Q ₁ .
Signal current due to reverse transfer capacitance Crss of S ₁ and FET Q ₁
At the same time that S ₂ flows, an induced current S ₃ flows in the coaxial resonator 11 in the opposite direction to that of the coaxial resonator 7 . These signal currents S ₁ to _{S 3} flow in the same direction as the signal currents S ₁ to _{S 3} shown in FIG. 1 of the conventional electronic tuning tuner, but
Due to the above connection, the signal current S ₂ flows into the coaxial resonator 11 in the opposite direction to that of S ₃ . Therefore, as shown in FIG. 4, the AGC characteristics of this embodiment are such that when it approaches the cut-off point of 1V, the signal current _S1 becomes extremely small and exhibits the maximum gain attenuation.
When the AGC voltage becomes 1V or less, the signal current S ₁ becomes 0, and only the signal current that can be considered 0, which is an extremely small difference between the signal currents S ₂ and S ₃ , flows through the coaxial resonator 11. Indicates the amount of attenuation. Therefore,
It is possible to eliminate the bounce of AGC characteristics.

FIG. 5 shows the second electronic tuning tuner according to the present invention.
A specific circuit diagram of the main part of the embodiment is shown. In the figure, the same parts as in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. One end of the coaxial resonator 7 is connected to the cathode of the variable capacitance diode 8', and the other end is connected to the first gate of the FET _Q1 via the capacitor 30. That is, in this embodiment, the connection arrangement of the coaxial resonator 7 and the variable capacitance diode 8' of the input tuning circuit of FET Q ₁ is changed, and when a signal current in the direction of S ₀ flows through the coaxial resonator 7, teeth,
The signal current is supplied to _{the first gate of FET Q 1 in} the opposite direction to that shown in Figs. The signal current flows in the direction shown by S ₁ ' in FIG. 5, and the signal current due to Crss of FET Q ₁ flows in the direction shown by S ₂ ' in the same figure. Further, the current induced in the coaxial resonator 11 flows in the direction indicated by _S3 .

Therefore, in the case of this embodiment as well, the unnecessary signal currents flow in opposite directions as shown by the arrows S ₂ ' and S ₃ .
It has AGC characteristics as shown in FIG.

The above is a case where the connection arrangement of one of the tuned circuits on the input side and output side of FET Q ₁ is changed.
In the embodiment and the fourth embodiment, both connection arrangements are changed. That is, in the third embodiment of the present invention shown in FIG. 6, the non-ground terminal of the coaxial resonator 7 is connected to the anode of the variable capacitance diode ₈ '', while Also, one end of the coaxial resonators 11 and 16 is grounded via the anodes and cathodes of variable capacitance diodes 12'' and 17'' and capacitors 32 and 33 in series.
2″ cathode is FET via capacitor 28
Connected to the drain of Q ₁ .

By making such a connection, in the case of this embodiment, when a signal current flows in the coaxial resonator 7 in the direction of arrow _S0 due to the high frequency television signal that enters the input terminal 2, the above-mentioned Unnecessary signal current due to Crss of FET Q ₁ flows in the direction of arrow S ₂ ′, and unnecessary signal current that is induced directly from the coaxial resonator 7 to coaxial resonator 11 flows in the direction of arrow S ₃ in opposite directions. Therefore, this embodiment also has AGC characteristics as shown in FIG. 4, like the first and second embodiments.

Furthermore, in the fourth embodiment of the present invention shown in FIG.
The first gate of FET Q ₁ is connected to the non-grounded terminal of coaxial resonator 7 and the anode of variable capacitance diode 8 via capacitor 35, and the drain of FET Q ₁ is connected to one end of coaxial resonator 11 via capacitor 28. and the anode of the variable capacitance diode 12, respectively. Also, variable capacitance diode 8
The cathode of the coaxial resonator 16 is connected to the ground via the capacitor 34, and the non-grounded terminal of the coaxial resonator 16 is connected to the anode of the variable capacitance diode 17.

In the fourth embodiment with such a connection, when a high frequency television signal flows through the coaxial resonator 7 in the direction of the arrow _S0 , the unnecessary signal current due to Crss of FET _Q1 flows in the direction of the arrow _S2 , causing coaxial resonance. The unnecessary signal current that is induced directly from the resonator 7 into the coaxial resonator 11 flows in the direction of arrow _S3 . As a result, the unnecessary signal current in the direction of arrow _S2 flows in the coaxial resonator 11 in the opposite direction to the unnecessary signal current in the direction of arrow _S3 . Therefore, the AGC characteristics of this embodiment are as shown in FIG. 4, similar to the first to third embodiments.

The AGC characteristics of the first to fourth embodiments described above are as shown in Fig. 4, and as a result of experiments, the degree of attenuation at the cut-off point is approximately the same over the entire band (from the 14th channel to the 83rd channel). It was confirmed that the size can be uniformly increased.

As described above, the electronic tuning tuner according to the present invention has a tuning voltage input terminal connected to one end of the first coaxial resonator in the input tuning circuit, and an input high-frequency signal current flowing through the first coaxial resonator. The tuning voltage input terminal is connected to one end of the second coaxial resonator in the output tuning circuit through which current flows by induction, and the input electrode of the high frequency amplification transistor is connected to the first coaxial resonator. Since it is connected to one end or the other end of the resonator, the output signal current component of the high frequency amplification transistor caused by the capacitance between the input electrode and the output electrode of the high frequency amplification transistor and the second coaxial resonator This allows the current flowing in the output tuning circuit to flow in opposite directions to each other in the output tuning circuit, thereby eliminating the downward peak near the cutoff point in the AGC voltage vs. gain attenuation characteristic. The image disturbance ratio of the conventional method is reduced by only about 2 dB compared to about 10 dB, which is a significant improvement.Furthermore, the degree of attenuation for AGC voltages below the cut-off point can be increased over the entire band, and the attenuation ratio can be significantly improved. The difference in power can be reduced over the entire band, making it particularly suitable for use in electronic tuning tuners that use MOS field effect transistors with large reverse transfer capacitance (feedback capacitance) as high-frequency amplification transistors. It has certain characteristics.

[Brief explanation of drawings]

FIG. 1 is a specific circuit diagram showing an example of a conventional electronically tuned tuner, FIG. 2 is a diagram showing an example of the AGC characteristics of FIG. 1, and FIG. 3 is a first embodiment of the electronically tuned tuner according to the present invention. FIG. 4 is a diagram showing an example of the AGC characteristics of the electronically tuned tuner according to the present invention, and FIGS. FIG. 3 is a specific circuit diagram showing main parts of the third and fourth embodiments. 1... Case, 2... High frequency television signal input terminal, 3... Tuning voltage input terminal, 4...
AGC voltage input terminal, 5...Power supply voltage input terminal,
6, 7, 9-11, 13-16, 18-20...
Coaxial resonator, 8, 8', 8'', 8, 12, 12',
12'', 12, 17, 17', 17'', 17...
...Variable capacitance diode, 26...Intermediate frequency signal output terminal, Q ₁ ...N channel 4-pole for high frequency amplification
MOS type field effect transistor, Q ₂ ...for mixed use
NPN transistor, Q ₃ ... NPN transistor for local oscillation.

Claims (1)

[Claims] 1. In an electronic tuning tuner in which a coaxial resonator is arranged as an inductance element in each of an input tuning circuit and an output tuning circuit of a high-frequency amplification transistor so that their longitudinal directions are parallel to each other, the first tuning circuit in the input tuning circuit A second tuned resonator in the output tuned circuit has a tuned voltage input terminal connected to one end of the coaxial resonator, and a current flows by induction due to the input high frequency signal current flowing to the first coaxial resonator. The tuning voltage input terminal is connected to one end, and the input electrode of the high frequency amplification transistor is connected to one end or the other end of the first coaxial resonator, and the output of the high frequency amplification transistor is An electronic tuning tuner characterized in that an electrode is connected to the other end or one end of the second coaxial resonator.