JPS5936023Y2 - tuner device - Google Patents

Description

[Detailed explanation of the idea] This invention relates to a tuner device.

FIG. 1 shows the main part of a high frequency amplification stage of a conventionally used television tuner.

In the figure, TRI is a high frequency amplification transistor, Dl.

D4 is a variable capacitance diode, D2. D3 is a switching diode for band switching, C2 and CIO are tracking correction capacitors, Ll, L2. L3, L4
is a tuning coil.

The high frequency signal applied to terminal A is transmitted through transistor TRI.
The signal is amplified by a double-tuned circuit, band-limited by a double-tuned circuit, and connected from a terminal J to a mixer stage (not shown).

To switch the receiving band, apply a positive or negative voltage between the terminals D2 and D2, and switch the switching diode D2. D
This is done by making 3 conductive or non-conductive.

Also, the reception frequency can be determined by applying a positive variable voltage to terminal H.
It is made variable by changing the capacitance of the variable capacitance diodes DI and D4.

In such a conventional high frequency amplification stage, a resistor R is connected from terminal F to
When applying an automatic gain control (AGC) voltage through 1,
As the emitter current of the transistor TRI changes, the collector-emitter voltage also changes, and as a result, the output capacitance CO of the transistor TRI changes, resulting in a drawback that the band characteristics of the double-tuned circuit fluctuate.

Additionally, there is a drawback in that tracking shifts and gain differences occur within the reception frequency band.

Figure 2 shows the local oscillator stage of a conventional tuner.
The transistor TR2 is an oscillation transistor, D6 is a switching diode for band switching, and Dl is a variable capacitance diode.

L5. L6 is a resonance coil, and C14 is a variable capacitor for tracking adjustment.

In this example, a common base type Colpitts oscillation circuit is configured, and the band switching voltage is applied from terminals M and N, and the tuning voltage is applied from terminal P.

The oscillation output is taken out from the emitter of the transistor TR2 via a capacitor C20 to a terminal S, and is coupled to a mixer stage (not shown).

In such a conventional local oscillation circuit, the operating point of the transistor TR2 changes depending on the frequency, and the voltage between the collector and base changes accordingly, the output capacitance of the transistor TR2 changes, and the tuning point moves. This caused malfunctions and unstable operation.

Also, when a strong input signal is received, a high level signal is transmitted from the mixer stage to the transistor TR via the capacitor C20.
It has disadvantages such as changing the bias between the base and emitter of the two, and as a result, the tuning frequency changes.

Therefore, the purpose of this invention is to avoid tracking deviation and tuning deviation, and when applied to a tuner of a television receiver, by adding a simple switching circuit means, the UHF band and VHF band can be switched. To provide a tuner device that can reliably switch bands.

FIG. 3 is a circuit diagram of a high frequency amplification stage for explaining the operation of the tuner device of this invention.

In the figure, transistor TR3 is a high frequency amplification transistor, D5 is a variable capacitance diode, R17 and R1
8 is a variable resistor that determines the bias of diode D5, C
21 is a DC blocking capacitor, and C23 is a bias capacitor.

Now, consider the case of receiving a strong input signal.

Forward AGC voltage is applied from terminal F, and transistor T
The emitter current of R3 increases.

Therefore, the voltage drop across the resistor R21 connected to the emitter of the transistor TR3 becomes large, and the voltage drop across the collector
The emitter voltage becomes smaller and the output capacitance component increases.

However, since an emitter voltage is applied to one end of the variable capacitance diode D5 and a constant negative voltage is applied to the other end via the terminal K, when the emitter potential increases in the positive direction, a deep reverse bias state occurs. Therefore, the capacitance component of diode D5 decreases.

When this increase in output capacitance is made equal to the decrease in capacitance of variable capacitance diode D5, the influence of output capacitance fluctuations is canceled out.

Resistors R19 and R20 are used to adjust the rate of change of the compensation capacitance.

The variable resistor R18 is used to set the operating point of the variable capacitance diode D5, and adjusts this value to perform tracking adjustment.

By doing this, the conventional variable capacitor C2 shown in FIG.
can be omitted.

Further, since the variable resistor R18 is used to change the DC voltage, it may be mounted at a position separate from the tuner body, increasing the degree of freedom in design.

Further, it is clear from the oscillator example described later that variations in the collector-base capacitance of the transistor can be compensated for using other grounded type amplifiers.

FIG. 4 is a circuit diagram of a local oscillation stage for explaining the operation of the tuner device of this invention.

In the figure, if a strong input signal is reversely injected from the terminal S, the emitter potential of the transistor TR4 decreases, the collector-emitter voltage of the transistor TR4 increases, and the collector-base capacitance decreases, but the variable capacitance diode DIO One end is connected to the emitter via resistors R24 and R26, and a constant negative voltage is applied to the other end via terminal X and variable resistor R27, so both ends of variable capacitance diode D10 are It becomes biased and its capacitance increases.

The rate of increase in the compensation capacitance can be adjusted by changing the ratio of the resistors R26 and R24, making it possible to cancel out the change in the collector-base capacitance of the transistor TR4.

The variable resistor R27 is for setting the operating point of the variable capacitance diode DIO, and is used to perform tracking correction.

In this example, in a common-base oscillation circuit, the base
Although an example has been shown in which variations in the capacitance between the collectors are compensated for, variations in the capacitance between the emitter and the collector can be compensated for by using a grounded emitter or collector type as in the case of the above-mentioned amplifier.

The tuner device of this invention compensates for fluctuations in the collector-base capacitance or collector-emitter capacitance of the transistor with such a simple configuration. If adopted, it will have even new functions.

FIG. 5 shows an embodiment in which the present invention is applied to a high-frequency amplification stage, and the portions surrounded by dotted lines differ from FIG. 3.

Now, if you turn the changeover switch SW1 to the Y side, the same operation as in Figure 3 will occur, but if you turn the changeover switch SW1 to the Z side and apply a positive voltage that is sufficiently larger than the emitter potential of the transistor TR5, the variable capacitance diode Dll becomes conductive, an additional current flows through the emitter resistor R28, and the emitter voltage of the transistor TR5 rises, causing the transistor TR5 to be cut off and inactive.

At the same time, the collector of transistor TR5 is connected to capacitor C2.
8, and will be grounded via C29.

By doing so, it is possible to switch between the VHF tuner and the UHF tuner.

That is, when receiving UHF, it is necessary to disable the high frequency amplification stage and local oscillation stage of the VHF tuner, but this operation can be performed reliably.

In other words, when applied to the high frequency amplification stage mentioned above, the UH
Since the IF amplification of the F tuner is performed in the mixer stage of the VHF tuner, there was a risk that this IF frequency component would leak through the high frequency amplification stage, but capacitors C28 and C in Figure 5
29. In Fig. 3, a transistor TR3 whose collector side is grounded in an alternating current manner by capacitors C21 and C23,
Since TR5 is cut-off, the amount of leakage can be reduced.

Also, if we consider the case where this idea is applied to a local oscillation stage, for example, when a sufficient positive voltage is applied through the resistor R25 in Fig. 4, the variable capacitance diode D10 becomes conductive, and the emitter potential of the transistor TR4 rises. However, the transistor TR4 is cut off and oscillation stops.

At the same time, the resonant circuit is short-circuited via capacitors C24 and C25, so oscillation is reliably stopped.

Normally, such UHF/VHF switching is performed by turning off the power to each circuit and leaving it inactive, but when a strong input signal is present, it is rectified by the pace emitter junction of the transistor, and the bias voltage is maintained even when the power is off. However, in this invention, the transistor is cut off, so a complete non-operation state can be achieved.

In the above explanation, only the VHF tuner was described, but the UHF tuner can also perform the compensation action and the UHF/VHF switching action, and especially when switching between UHF/VHF, each tuner Reliable switching is possible by differentially operating the changeover switch SW1 provided in the switch SW1.

In addition, in the above explanation, a junction type transistor is used as an active wife and a variable capacitance element, and a variable capacitance diode is used as a variable capacitance element. Needless to say, similar effects can be expected.

As described above, according to the tuner device of this invention, although the circuit configuration is simple, the following effects can be expected.

(1) Fluctuations in capacitance between transistor electrodes can be compensated for, so tuning deviations and tracking deviations do not occur, and receiver characteristics do not change.

(2) In television receivers, it can be used as a switching circuit when multiple tuners are built in, such as UHF/VHF band switching, and compared to the conventional method of switching by turning the power ON or OFF, it is especially useful when a strong input signal is present. This enables more reliable switching.

In addition, the DC voltage obtained at the output end of the capacitance element is applied to one end of the variable capacitance element, and the other end is connected to two voltage sources of different polarity so that the variable capacitance element is in a forward bias or reverse bias state. Because it is configured so that two voltage sources of different polarity are switched and selected by a switch circuit, it is possible to easily put the main active element into a non-operating state, and the variable voltage source for tuning This has the effect of increasing the degree of freedom in design compared to applying a correction voltage directly to the capacitive element.

In other words, the output capacitance is constant regardless of frequency, but
Since the controlled sensitivity of the channel selection variable capacitance element changes depending on the frequency, the practical value can be increased by a configuration in which output capacitance correction is performed using a separately provided compensation element.

[Brief explanation of drawings]

Figures 1 and 2 are a high frequency amplification stage and a local oscillation stage of a conventional tuner device, respectively, Figure 3 is a circuit diagram of the high frequency amplification stage for explaining the operation of the present invention, and Figure 4 is an explanation of the operation of the present invention. FIG. 5 is a circuit diagram of a high frequency amplification stage according to an embodiment of the present invention. TR3, TR4, TR5...Transistor, D
5゜DIO, Dll... Variable capacitance diode,
R18, R27...Variable resistor, SWl...
...Selector switch.

Claims (1)

[Scope of utility model registration request] When a tuned circuit is loaded, a transistor, a voltage variable capacitance element connected in parallel to the tuned circuit at high frequency and one end connected to the emitter of the transistor in a direct current manner, and a voltage variable capacitance element connected to the other end of the voltage variable capacitance element in a direct current manner. a switch circuit that is connected to selectively apply two sets of DC bias voltages of different polarities to the voltage variable capacitor, one of the two sets of DC bias voltages forward biasing the voltage variable capacitor. A tuner device set to a voltage that makes it conductive.