JPH0156567B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic tuning tuner using a variable capacitance diode.

The tuner in television receivers changed from a mechanical type to an electronic type, and television receivers became more multifunctional.
Diversification is progressing rapidly. The use of electronic tuners in television receivers allows for greater freedom in design and combinations of functions, performance, and cost, making it possible to create a variety of product plans. Demand for features such as remote controls, program reservations, and direct access, as well as a wide range of functions such as dial selection and search selection, has led to a wide range of products from 1.5-inch devices to video projectors, as well as complex products such as 3-in-1 systems. It is.

As television receivers have improved in functionality, their use has expanded to include familiar video equipment for information, education, and entertainment.

There are multiplex receptions and multichannel receptions that aim to expand information, and the representative example is the two-language, stereo reception by audio multiplex broadcasting that began in Japan in 1973, and further developed into text multiplex broadcasting, and still image reception. It is thought that the use of fax machines will lead to a CATV system.

Pay TV and CATV are rapidly developing in the United States and Europe, and the trend toward multichannelization is more pronounced than the increase in the amount of information. For example, America
Canada's CATV channel is a traditional channel
In addition to 82 stations (12 VHF stations, 70 UHF stations), 23 stations (channels A to W) have been allocated, making a total of 105 stations. Of course, even more reports are being made regarding this channel plan. CATV channels are similarly allocated in Europe, and are actually being used in countries such as Belgium, Austria, and Switzerland.

The present invention relates to an electronically tuned tuner for a television receiver that can accommodate frequency (channel increase) expansion.

CATV channel reception TV receivers mainly in the United States and Canada have been available since 1978, and are not only TV receivers dedicated to pay TV networks and CATV systems.
It appeared on the market as a "TV receiver capable of all-band reception" in general consumer advertising, and is stimulating demand for future possibilities and actual systems.

For CATV channels in the US and Canada,
As shown in Figure 1, VHF Low Band, High
Band, UHF Band, Mid Band and Super
Band has been added and its frequency is 120MHz to 174MHz
is Mid Band, and 216-300MHz is Super Band. Similar to the United States, CATV bands in Europe are expanding their channels by using Mid Band and Super Band. Naturally, this trend is likely to occur in Japan in the future, but the channel plan will use Mid Band and Super Band. this
In order to receive CATV channels, conventional TV tuners cannot receive the signals, and a new broadband receiving (all-band) tuner is required. Of course, it is possible to realize an all-band tuner using a mechanical tuner, but due to structural constraints and lack of flexibility in additional functions, it is unlikely that an electronically tuned tuner will be used in the future. It is also more effective in terms of functionality than remote control use or direct access synchronized with frequency synthesizer tuning.

The following three methods are considered to be typical for realizing the above-mentioned all-band tuner using an electronically tuned tuner.

(A) A total of 4 band system in which the VHF band is switched to 3 bands and the UHF band is received in 1 band as before.

(B) Conventional 3-band system in which the VHF band is switched to 2 bands and UHF signals are received in 1 band as before.

(C) Adopts double superheterodyne method,
Receives VHF and UHF in one band, or two-band system with one VHF band and one UHF band.

In the case of an electronically tuned tuner, the desired frequency is varied using a varicap (variable capacitance diode), so the receivable range is naturally limited by the variable capacitance range of the bicap. For example, when calculating the receivable range using the conventional tuner tuning circuit (equivalent circuit) shown in Figure 2a, from the formula ( _H / _L ) ² = C _T + C _DL / C _T + C _DH [ _H : highest receiving frequency, _L : lowest receiving frequency,
C _T : External additional capacitance + stray capacitance, C _DL : Varicap capacitance at tuning voltage 1V, C _DH : Tuning voltage 25V
When the varicap capacitance at time is C _T = 7 pF, C _DL = 33 pF, and C _DH = 2 pF, the frequency ratio _H / _L = 2.1. In other words, the lowest receiving frequency channel in the VHF band of the conventional receiving channel.
ch2 = 55MHz, highest receiving channel ch13 = 210M
If it is Hz, it requires a frequency ratio _H / _L ≒ 3.8, so it is not possible to receive from ch2 to ch13. In Fig. 2a, C _D is a variable cap, and L is a tuning coil. Therefore, conventionally, as shown in FIG. 2b, a switching diode (SWD) is used between the Low Band and the High Band to switch between the High Band tuning coil L _H and the Low Band tuning coil _LD . In this case, the frequency ratio of each band is Low
Band (ch2 to ch6) _H = 82MHz / _L = 54MHz≒
1.52, High Band _H = 216MHz/ _L = 174MHz≒
1.24, and reception via variable cap is possible. In this case, the varicap used also has a tuning voltage of
There is no need for a large capacitance ratio that varies from 2 to 33 pF in the range of 1 V to 25 V, and reception is possible even with a varicap that varies from 2 to 16 pF.

However, in the case of all-band reception, _H = 300MHz
_L = 120MHz, requiring _H / _L = 2.5, using switching diodes, and low band
Even if it is divided into High Band, High Band
It becomes impossible to receive from chA to chW, and new circuit development is required.

Among the above three methods, method A is High Band
is further divided between 120MHz and 300MHz in the same way as before, and the reception frequency ratio by the varicap is set to _H /300MHz.
This is what we are trying to achieve as _L 2.1. Therefore, Low Band, High Band1 and High Band2
and UHF Band, making it a total of 4 band systems.

The above method B has _H / _L = 2.5 by circuit development,
In this implementation, band switching is performed in 3 bands as in the past.

Method C is considered for the future, and involves up-converting the desired frequency to, for example, the UHF band and down-converting it again to obtain an intermediate frequency. For example, if a frequency of 54MHz to 300MHz is up-converted to an intermediate frequency of 350MHz, the local oscillation frequency is 404MHz to 650MHz.
It is possible to receive the entire VHF range with a variable Hz range.
Although this method still faces various problems, it is a method that is seen as promising for the future.

The present invention relates to the method B,
High Band _H / _L = 2.1 (120MHz to 300MHz continuous reception) is achieved by developing a tuning circuit.

As mentioned above, in order to achieve a ratio of 2.5, even a currently developed variable cap with the highest capacity ratio can only receive up to a ratio of 2.1. If we consider a method of expanding the reception range by inserting two varicaps in parallel to the tuned circuit, the varicap capacitance will change within a range of 4 to 66 pF, giving _H / _L = 2.58, which means that the reception range can be covered, although there is not much margin. Become. However, the tuning capacitance is especially low around the tuning voltage of 1V.
It is close to 70pF, and the loss in the tuning circuit is large, resulting in gain differences in the band and deterioration of the noise figure, making it unusable. Therefore, the present invention is realized by inserting first and second variable caps C _D1 and C _D2 in parallel and in series with the tuning coil L, as shown in the equivalent circuit shown in FIG. 3a. In other words, the tuning coil L has a second
Varicaps CD ₂ are connected in series, and a first varicap CD ₁ is connected in parallel to this series connection. According to the tuning circuit in Figure 3a, ( _H / _L ) ² = C _D2L (C _D1L + C _T )/
According to the formula CD1L + C _D2L +C _T /C _D2H (C _D2H +C _T ) /C _D1H +C _D2H +C _T , C _T =7pF, C _D1L =C _D2L =33pFC _D1H =
If C _D2H = 2p ^F , _H / _L = 3.32, which satisfies the frequency change range and enables reception from 120MHz to 300MHz. Furthermore, the insertion loss of the tuned circuit is the same as that of conventional circuits, and the same performance can be obtained. The frequency characteristics of the circuit of the invention are shown in FIG. 3b. This circuit has a desired tuning frequency _{of 2} (ω ₂ points in the diagram)
On the other hand, a series resonance trap ₁ (ω ₁ point) is formed in the lower channel. _The frequency characteristics are expressed as ω ₁ ² = 1/LC _D2 ω ₂ ² = 1/L (C _T + C _D1 ) + 1/LC _D2 , and the relationship between the trap frequency and the desired tuning frequency is ( _2/1 ) ² = 1 + C _D2 /C _T +C _D1 In the reception area where C _T <C _D1 , C _D2 , a large amount of attenuation is obtained for frequencies that are 1/2 relative to the desired frequency ₂ . When complex signals are applied to the input of electronically tuned tuners, etc., second-order and third-order distortions caused by devices in the RF amplification stage become a problem. In this case, the secondary distortion is significantly improved, and the ability to eliminate disturbances such as beat disturbances can be significantly improved. Especially in the case of all-band reception, there are many 1/2 frequency relationships within the same band.
For example, 120MHz (chA) and 240MHz (chN), etc., and problems that did not occur with conventional band allocation will occur in all-band reception, and the present invention is an effective circuit for these problems as well. . FIG. 4 shows a circuit of an electronically tuned tuner for all-band reception according to an embodiment of the present invention.

In Figure 4, A is the VHF input terminal and B is the VHF input terminal.
VHFIF output terminal, C is IF trap circuit, _Q1 is
MOSFET for RF amplification, Q ₂ and Q ₃ are cascode-connected mixer transistors, Q ₄ is an oscillation transistor, B _S is a switching power supply terminal,
B _T is a power supply terminal for tuning, B ₁ is a power supply terminal for the RF stage and oscillation stage, B ₂ is a power supply terminal for the mixer, AGC is a terminal for automatic gain control for RF amplification, C _D1 and C _D2 are varicaps for tuning, SWD is a switching diode, L ₁ ,
L ₄ , L ₅ , L ₇ , L ₁₁ are High Band tuning coils,
L ₂ , L ₃ , L ₆ , L ₈ , L ₁₂ are Low Band tuning coils, L ₉ is a coupling coil in the Low Band of the interstage tuning circuit, L ₁₀ is an IF output tuning transistor,
_L13 is the load inductance of the RF amplification stage, _L14 is the collector inductance of the oscillation stage, _R1 , _R10 , _R11 ,
R ₂₃ is a switching resistor, R ₂ , R ₉ , R ₁₂ , and R ₁₈ are tuning voltage supply resistors, R ₃ , R ₄ , R ₆ , and R ₈ are bias resistors for the RF amplification stage, and R ₅ is an AGC resistor. , R ₁₃ , R ₁₄ ,
R ₁₅ , R ₁₆ , R ₁₇ are bias resistors for mixer, R ₂₁ ,
R ₁₉ , R ₂₀ , R ₂₂ are bias resistors for the oscillation circuit, C ₁ ,
C ₆ , C ₇ , C ₁₈ are DC blocking capacitors for switching circuits, C ₂ , C ₅ , C ₈ , C ₁₇ are coupling capacitors,
C ₃ , C ₄ , C ₂₆ , C ₂₇ , C ₁₃ , C ₁₆ are high frequency bypass capacitors, C ₁₉ , C ₂₀ , C ₂₁ , C ₂₂ , C ₂₃ are feed-through capacitors for bypass, C ₉ is for oscillation injection The capacitor _C12 is the mixer output capacitance, and _C15 and _C14 are the feedback capacitors for oscillation.

The electronic tuning tuner shown in FIG. 4 has the following features.

(1) In order to insert the variable caps C _D1 and C _D2 in parallel and series with the tuning coil L as shown in Figure 3a,
All-band reception is possible with plenty of time.

(2) Varicaps C _D1 and C _D2 use matched varicaps with the same characteristics to track the RF response in each stage circuit of the electronically tuned tuner, but depending on the receiving range, the varicaps of the C _D1 series and C _D2 can be used. Varicaps from the series can also be used separately.

(3) Changes in the bandwidth and noise figure at the receiving frequency in a conventional circuit and a circuit in which all-band reception was attempted using two varicaps in parallel, and changes in the bandwidth and noise figure in the circuit of the present invention. It is shown in FIG. The circuit C of the present invention has a small change in Q, and can prevent large insertion loss and large gain difference due to changes in Q as seen in the conventional circuit. It also has the great advantage that the frequency band characteristics in all channels of all-band reception can be kept uniform. In conventional circuits, the frequency band inevitably widens in the high frequency channel and narrows in the low frequency channel, making it impossible to obtain sufficient band characteristics and frequency selectivity characteristics.

(4) The lower selectivity near 1/2 of the desired signal is greatly improved by the series trap, and second-order distortion interference can be greatly improved.

(5) For all-band reception, the highest reception frequency is
300MHz, and it is impossible to wind the tuning coil L because it is performed using a lumped constant circuit. When realized with the circuit shown in Figure 5 B, L is the wire diameter that cannot be wound.
0.6φ and the winding diameter is 2.0φ, it is about 0.8 ^T , and the RF response cannot be adjusted by changing the coil. In contrast, the circuit of the present invention uses a varicap.
Due to the effect of C _D2 , winding is possible and the wire diameter
With a winding diameter of 0.6φ and a winding diameter of 3.0φ, a large winding coil of about 5T is possible, and conventional RF adjustment methods can be fully applied. Not being able to wind L in an actual circuit is a fatal problem.

(6) Since the circuit of the present invention enables extremely wide reception with _H / _L = 3.32, there is plenty of room for external additional circuits (C _T : about 7 pF), and it is suitable for devices with large input and output capacitances and circuit selectivity. As a result, it becomes possible to create large-capacity circuits, allowing greater freedom in design and approaches to higher performance.

(7) The reception range is extremely wide, and the tuning coil for the highest frequency can be sufficiently wound, so it can cope with the trend of higher frequency expansion. _H / _L
= 3.32, the maximum receivable frequency reaches 396 MHz, which results in an additional channel expansion of 16 channels.

As described above, the present invention enables multi-channel reception, which could not be achieved with conventional circuits, and has the advantage that it can be achieved while maintaining the conventional varicap, conventional circuit system, and conventional production system. Further, according to the present invention, the performance can be increased and there is no increase in cost, and rather the production cost can be reduced. Furthermore, in the present invention, a plurality of first variable capacitance diodes or a plurality of second variable capacitance diodes connected to respective tuning coils provided in the input circuit, the interstage tuning circuit, and the local oscillation circuit have the same characteristics. This simplifies the work of adjusting the frequency characteristics at each stage.
This results in high productivity.

In other words, the capacitance value of both the first and second variable capacitance diodes is made variable depending on the applied voltage value, but in the present invention, each of the first variable capacitors used in the above three circuits Diodes or second variable capacitance diodes having the same "voltage-capacitance characteristics" are used. To explain in more detail, in each stage, for each desired channel, the first,
By varying the voltage applied to the second variable capacitance diode, the respective capacitance values of the first and second variable capacitance diodes are determined.
In this case, the frequency characteristics between each stage must of course be well-adjusted, so the first stage input circuit usually uses, for example, an "X channel".
When deciding how many volts to apply in each case, it is also necessary to decide how many volts to apply to the interstage tuning circuit and the local oscillation circuit in the same way to achieve a tuned result.

However, at this time, if the "voltage-capacitance characteristics" of the first variable capacitance diodes or the second variable capacitance diodes in these three stages are different, the first and second variable capacitance diodes of the input circuit in the "X channel"
After determining the voltage value to be applied to each of the variable capacitance diodes, it is necessary to determine the voltage value to be applied to each of the first and second variable capacitance diodes in the interstage tuning circuit and local oscillation circuit, respectively, which requires adjustment work. becomes very troublesome.

Moreover, this adjustment work requires deciding one by one how many volts to apply to the first variable capacitance diode in each stage, and how many volts to apply to the second variable capacitance diode at each stage. This was a time-consuming task.

This is necessary for the desired number of channels, so in reality, even adjusting just one unit is a huge amount of work. This had to be done from scratch for each set, making it a really difficult task.

On the other hand, as in the present invention, the first of these three stages
If the "voltage-capacitance characteristics" of the two variable capacitance diodes or the second variable capacitance diodes are the same, the voltage applied to the first and second variable capacitance diodes of the input circuit during "X channel" Once this is determined, the voltage applied to the first and second variable capacitance diodes in the other two stages can be applied as is, and of course, if the set is "X channel", this voltage can be applied. Since there are a large number of channels, this can significantly reduce the working time. This has an extremely large effect during mass production.

[Brief explanation of drawings]

Figure 1 is a diagram showing the frequency of American TV reception channels, Figure 2 a and b are equivalent circuit diagrams of the tuning circuit of a conventional electronically tuned tuner, and Figure 3 a
is an equivalent circuit diagram of the tuning circuit of the electronically tuned tuner of the present invention, FIG. FIG. 3 is a diagram showing the bandwidth and noise figure of the conventional example and the present invention. C _D1 , C _D2 ...variable capacitance diode, L...tuning coil.

Claims (1)

[Claims] 1 Input circuit, in order, amplifier circuit, interstage tuning circuit,
An output circuit is connected through a mixer, a local oscillation circuit is connected to the mixer, a tuning coil is provided for each of the input circuit, the interstage tuning circuit, and the local oscillation circuit, and a second tuning coil is provided for each tuning coil. In addition to connecting variable capacitance diodes in series,
A first variable capacitance diode is connected in parallel to each of the series connections of each of these tuning coils and a second variable capacitance diode, and a plurality of first or a plurality of second variable capacitance diodes are matched to have the same characteristics.