DE3150625A1 - TUNER - Google Patents

Description

Description: 81/87116

The present invention relates to a tuner, in particular a tuner capable of receiving input signals received within a wide frequency range.

The well-known tuner commonly used in television receivers is used, corresponds to a simple overlay receiver and comprises a mixer, a local oscillator and an intermediate frequency (IF) filter. A television signal, which in the case of normal television broadcasting from the antenna, in the case of cable transmission (CATV) received over a cable, is received over a radio frequency (HF) amplifier is fed to an input of the mixer stage. To the other input of the mixer is a signal from the local oscillator, whose Frequency corresponds to the desired channel.

The mixer generates signals, the frequencies of which are the sum and the difference between the frequencies of these two input signals correspond. The IF filter is designed so that only one of the two produced by the mixer stage Signals pass through, and only that whose frequency is the difference between the frequencies of the two input signals is equivalent to. As a result, the IF signal of the television signal whose frequency corresponds to the selected channel arrives through the IF filter. The frequency supplied by the local oscillator has a range that corresponds to the frequency range of the input television signal.

Television broadcasting today includes VHF, UHF and CATV transmissions. VHF transmissions' are divided into a low band extending from channel 2 to channel 6 and a high band extending from channel 7 to

Channel 13 ". The low band covers a range of frequencies of the video carrier from 55.25 MHz to 83.25 MHz and the high band a frequency range from 75.25 MHz to 211.25 MHz. The UHF transmission covers channel 14 to channel 83 and has a frequency range from 471.25 to 885.25 MHz on. The CATV transmission is divided into a medium band from channel A to channel I, a superband from channel J to channel W and a hyperband from channel X to channel M13 and comprises the frequency ranges 121.25 to 169.25 MHz for the medium band, 217.25 to 295.25 MHz for the super band and 301.25 to 403.25 MHz for the hyperband. If now a single-stage tuner is receiving all of these television broadcasts is to enable, the frequency of the local oscillator must be changed over a wide range so that they are matched to the input signals in the wide ■ frequency range from 55.25 to 403.25 MHz can.

The oscillation frequency f of an LC oscillating circuit results from L being the inductance and CC being the equivalent capacitance and CV denote the variable capacity, from the following equation:

f = ~ - ■ (1)

2τι VL (CV + CC)

wherein the inductance is connected in parallel with the equivalent capacitance CC and the variable capacitance CV. The spare capacity CC has a fixed value and represents the stray capacitance of the circuit. Provided that that the maximum and minimum values of the variable capacitance of the resonant circuit are denoted by CVmax and CVmin, respectively the maximum and minimum values fmax result and fmin is the oscillation frequency according to the equation (1) as follows:

315Ö625

fmax = (2)

2tW L (CVmin + CC)

fmin =

2π4 L (CVmax + · CC) It follows from equations (2) and (3)

fmax / fmin = / CVmax + CC _{4)

ν cvmin + CC

From this it follows that the change behavior (fmax / fmin) of the oscillation frequency of the oscillating circuit increases,

^ if - increases. The smaller the fixed frequency

CC becomes, the larger the change ratio becomes.

The ratio of changes in the capacitance of a component with variable capacity, e.g. one practical today used capacitance diode, but is not particularly large. The change ratio (CVmax / CVmin) is im In the case of common products, it reaches around 5.0 and for products that have a large change ratio, only about 9.7. Assuming that CC has a value of 3pF, the equation gives. (4) a change ratio the vibration frequency: from T, 65 for average Components "and one of only about 2.31 when using components with a large Change ratio. When the IF signal is 45.75MHz, as is the case in the USA (58.75 MHz in Japan and 38.75 MHz in West Germany), the frequency of the local oscillator must be in the range from 101 to 931 MHz can be changed so that an IF signal is produced, which is the difference in frequency between the. Input signal

in the range from 55.25 to 885.25 MHz and corresponds to the beat frequency. In this case the frequency ratio is about 9 and a corresponding local signal can be generated with a simple local oscillator cannot be generated. Therefore separate tuners are provided for VHF, UHF and CATV. The inductance of the The resonant circuit is used for each of the VHF, UHF and CATV bands (low and high bands of VHF and UHF, medium, CATV super and hyperbands) changed. However, when using 'JO such a construction, the arrangement becomes voluminous and the circuit complicated in structure because of the required switching device.

To avoid these disadvantages, the use of a

-j5 two-stage overlay tuners considered which one two simple overlay tuners are connected in series. One of these local oscillators is variable in frequency, the other is fixed, usually the frequency of the first one connected to the input Local oscillator variable. The television signal and the output signal of the first local oscillator are mixed in a first mixer stage and this first mixer stage generates together with one at its output connected first IF filter a first IF signal whose fixed frequency is higher than that of the usual IF signals. The first IF signal and the output signal of the second local oscillator, which has a fixed frequency, are mixed in the second mixer, and the second mixing stage produces along with one of theirs

3Q output connected second IF filter a second IF signal, which corresponds to the usual IF signal. Because the frequency of the first IF signal is higher than that of the usual IF signal, the oscillation frequency of the first local oscillator is in a range higher Frequency. When the frequency range is high, the

Range in which the frequency is changed widely even if the change ratio of the oscillation frequency remains the same. For example, if the first IF signal is 3 GHz, the oscillation frequency is the first local oscillator in the range of 3055.25 to 3885.25 MHz. The change ratio of the Oscillation frequency in this case is about 1.3 and even a simple tuner can do all television broadcasts paint over sufficiently.

However, if the first intermediate frequency is set high, it means that the center frequency of the first IF filter is set high. If the center frequency is high, Q must be made large so that the filter characteristic becomes steep, however, the extent to which Q can be made large is limited. Therefore, if the center frequency is around 3 GHz, only a filter with a poor filter characteristic can be implemented, with the result that unwanted transmission signals from neighboring channels are received. In practice it will the output of the first IF filter of the second Mixer fed via an IF amplifier. The gain of this IF amplifier, however, is when the first Intermediate frequency is high, small, with the result that the S / N ratio of the whole tuner deteriorates will. On the other hand, if the first intermediate frequency is chosen low, the first beat frequency low, making it impossible for a simple tuner to sweep all television broadcast bands.

In contrast to the design described, a two-stage superposition tuner is also considered, in which the first local oscillator is a fixed one Frequency and the second local oscillator have a variable frequency. The center frequency of the first

In this case, however, the IF filter must be set to a value which corresponds to the desired channel, and the implementation of such a filter is also possible difficult.

The aim of the present invention is a tuner which, when using an oscillator with a variable Frequency is able to receive signals in a wide frequency range.

This object of the present invention can be achieved with a tuner consisting of a first oscillator, whose frequency is variable, a second oscillator with a first fixed frequency which is lower than the lowest frequency of the first oscillator, a mixer for mixing the output signals of the first and a second oscillator, a first frequency converter for converting a high-frequency input signal into a signal with a second fixed frequency using the output signal of the mixer and a second frequency converter for converting the output signal of the first frequency converter into an intermediate frequency signal at a fixed frequency lower than the second fixed frequency using the output signal of the second oscillator.

Fig. 1 shows a block diagram for an embodiment a tuner according to the present invention and

FIG. 2 is a circuit diagram showing the main part of the tuner shown in FIG. 1 in detail.

An exemplary embodiment of a tuner according to the invention is described with reference to the figures. In Fig. 1, an input 10 is connected to a not shown

• j antenna or a cable (not shown) of a CATV connected is connected to the input of an RF amplifier. 12, the output of which is connected to the first input of a mixer 14. The output of a local oscillator 16, the frequency of which is variable, is connected to the first input of a mixer 18, whose Output is connected to the second input of the mixer 14. The frequency of the local oscillator 16 is set higher than that of the usual tuner in

-jO the design of a simple heterodyne receiver with the aim that the range of the frequency change becomes large even when the ratio of the frequency change is small is. An output of an oscillator 20 with a fixed frequency is connected to the second input of the mixer 18.

Ί5 The mixers 14 and 18 superimpose first and second input signals and generate "two signals whose Frequencies correspond to the sum and the difference of the frequencies of the first and second input signals. Under the Prerequisite that the difference signal is generated by the mixer 18, the oscillation frequency of the Local oscillator 16 can be selected to be the frequency of the oscillator 20 higher than in a conventional tuner the design of the double heterodyne receiver without the first intermediate frequency is set high. The output ■ signal of the mixer 14 is through an IF filter 22 and the IF amplifier 24 connected in series is fed to the first input of a mixer 26. The IF filter 22 is a band pass that only lets through a first IF signal whose frequency is greater than that of the usual one IF signal. The mixer 14 and the IF filter 22 act as the first frequency converter that converts the input RF signal into the first IF signal. Since the center frequency of the IF filter 22 is large, it is called an IF filter 22 a surface acoustic wave filter is used.

In the present embodiment, however, is the first

Intermediate frequency lower than that of the conventional tuner of the type of double heterodyne receiver, so that the Q of the intermediate frequency filter 22 can be realized. The output signal of the oscillator 20 is fed to the second input of the mixer stage 26. Similar to the mixing stages 14 and 18, the mixing stage also generates two signals whose frequencies correspond to the sum and the difference of the frequencies of the two input signals. The output signal of the mixer 26 is fed to the output 30 via an IF filter 28. The IF filter 28 is also a band pass which only _{lets through a second IF signal f,} ie the usual IF signal. Mixing stage 26 and IF filter 28 serve as a second frequency converter for converting the first IF signal into the second IF signal.

The operation of the present embodiment will now be described. The oscillation frequency of the local oscillator 16 is set to a frequency corresponding to the desired channel. If the frequency of the local oscillator is changed between the values F1min and F1max and the frequency of the oscillator 20 is F2 (F2 <F1min), the frequency of the mixer 18 changes as follows, the suffixes "max" and "min "identify the maximum and minimum values: the difference signal F3 changes from F3min (= F1min - F2) to F3max (= F1max - F2), the sum signal F3 ¹ from F3'min (= Fimin + F2) to F3'max (= F1max + F2). Since the output signal of the mixer 18 continues to be mixed with the input RF signal in the mixer 14, if the frequency of the input RF signal is denoted by Fin, the following output signals from the mixer 14 result: The Difference signal F4 is F3 - Fin or F3 '- Fin and the sum signal F4' results in F3 + Fin or F3 '+ Fin.

Since the frequency F3 or F3 'of the output signal of the

Mixer 18 has changed according to the selected channel, - the output frequency F 4 or F4 'of the mixer 14 can always be kept constant regardless of the selected channel. The IF filter 22, which is easy to manufacture, lets through only the difference signal (F4 = F3 - Fin) of the output signals of the mixer 14 and blocks the sum signal (F4 ¹ = F3 + Fin) as well as unwanted signals, e.g. signals from neighboring channels that reach the IF filter 22. The output signal of the IF filter 22 thus becomes the first IF signal with the frequency F4. Even if the beat frequency FT is large, the frequency F4 can be set to be low because the frequency F3 involved in the formation of the first IF signal is F2 lower than FI. The IF filter 22 can therefore, without

Ί5- that Q is very large, have a digit characteristic and the unwanted signals can be prevented from passing through the IF filter 22. The output signal of the IF filter 22 reaches the mixer 26 via the IF amplifier 24 and is there with the output signal of the oscil- lators 20 superimposed. The output signal of this mixer stage arises as a difference signal · F5 = F4 - F2 or as s sum signal F5 '= F 4 + F2. For a reason that will be described later, the IF filter 28 only allows the difference signal · F5 = F4-F2 to pass. That of that ZF-Fiiter 28 signal with frequency F 5 is muted the second IF signal, i.e. the usual IF signal, which is sent via output 30 to a video detector (not shown) is fed.

In the following description, for each circuit section a practical frequency value is given. The frequencies of the input RF signal · s and the second IF signal result from themselves. Furthermore, it is assumed in this example that a ^ e TV transmission types, how VHF, ÜHF and CATV are received. Accordingly

measure moves the frequency pin of the input RF signal in the range from 55.25 MHz to 885.25 MHz and the frequency F5 of the second IF signal is 45.75 MHz. The through the The frequency of the first IF signal passing through the IF filter 22, i.e., the frequency F4, is set to 450 MHz and thus allows a sufficiently steep characteristic curve of the SAW filter. Since F2 = F4 - F5 results for the Frequency F2 of oscillator 20 is the value of 404.25 MHz. The mixer 14 superimposes the input RF signal the output signal of the mixer 18 and the difference signal of 450 MHz is from the IF filter 22 from the sum and difference signals at the output of the mixer 14 filtered out. Accordingly, the output frequency moves F3 of mixer 18 in the range between 505.25 MHz to 1335.25 MHz. Since the output frequency F3 of the mixer 18 moves in the range 505.25 MHz to 1335.25 MHz, the frequency F1 of the output signal of the local oscillator can change 16, which is mixed in the mixer 18 with the signal from the oscillator 20, in the area between 909.5 MHz to 1739.5 MHz (the mixer stage 18 forms the difference and generates a signal in the range 505.25 to 1335.25 MHz {= F3)) or in the range from 101 MHz to 931 MHz (the mixer 18 forms the sum and generates move the signal between 505.25 and 1335.25 MHz (= F3 ')). In the latter case, the frequency change ratio reaches almost the value 9 and the signal of the local oscillator can not with the help of a single element variable capacity can be generated. In the former case, however, the frequency change ratio is as the frequency is high, about 1.9 and the local oscillator 16 can therefore be realized using a single commercially available variable capacitance element.

That. The output signal of the local oscillator 16 is so with the aid of the mixer 18 using the

Output signal of the fixed frequency oscillator 20 in a signal with a lower frequency converted. and the input RF signal is converted with the help of mixer 14 and IF filter 22 converted into the first IF signal using the output signal of mixer 18. this makes possible it that the frequency of the local oscillator 16 is set to a high value and that a Local oscillator signal sufficient to process an input RF signal in a wide frequency range can be realized even if the capacity ratio, i. H. Frequency change ratio, of the local oscillator is small. In addition, the first intermediate frequency need not be very high. As a result, the IF filter 22 can be realized with a steep characteristic curve, thus preventing signals other than those of the desired channel, e.g. signals from adjacent channels or those with other channels Vibrational frequencies, get through. This enables a simple tuner (or oscillator with a variable frequency signal) to receive all TV transmission channels.

The circuit diagram in Fig. 2 shows the somewhat more detailed Local oscillator 16, the mixer 18 and the Oscillator 20.

In the local oscillator 16, the base is one NPN transistor 32 connected to ground via the parallel connection of a resistor 34 and a capacitor 36, its emitter is also connected to ground via the resistor 38, while its collector is connected via an inductance 40 is at the power supply input VCC. A capacitor 42 is connected between the emitter and collector of the transistor 32, the collector of which via the capacitor 44 is connected to one end of the inductance 46, which acts as a resonance element. Same ending

the inductance 46 is connected to ground via the capacitor 48 and to the input VT via the resistor 50 connected for the tuning power supply. The other end of the inductor 46 is across the capacitor 54 to ground and at the same time to the cathode of the capacitance diode 52 / which is used to change the frequency. The anode the capacitance diode 52 is connected to ground. An inductance 56, both ends of which are connected to ground and those of fine adjustment is arranged in close proximity to the inductance 46, the distance between the inductances 56 and 46 is changeable. The base of the transistor 32 is connected via a resistor 58 to the terminal VCC connected to the power supply, which in turn is connected to ground via capacitor 60.

In the mixer 18, a coupling inductance 62, one end of which is grounded, is in spatial proximity to the Inductance 46 of the local oscillator 16 is arranged. The other end of the inductor 62 is connected to the Anode of a mixing diode 64 connected, the cathode of which has

a coupling inductance 66 and a capacitor 68 : is connected to mixer 14.

In the oscillator 20 is the base of an NPN transistor 70 via the parallel connection of a resistor 72 and one Capacitor 74 is connected to ground and connected to the power supply input VCC via resistor 76. Of the The emitter of transistor 70 is connected to ground via resistor 78 and its collector is at the same time via inductance 80 to the input of the power supply VCC and via the capacitor 82 to one end of the inductor 84 connected, which serves as a resonance element. A capacitor 86 is connected between the emitter and collector of transistor 70. The inductance 84, whose one end through capacitor 88 and the other end thereof

are connected to ground via the resonance capacitor 90, is in spatial proximity to the inductance 6 * 6 in the mixer stage 18 arranged. In close proximity to inductance 84 and with a variable distance to this is an inductance 92 arranged, which is used for Peineeinstellung and both ends of which are connected to ground. Also in spatial An inductance 94 is arranged close to the inductance 84, one end of which is connected to ground and the end of which is connected to ground the other end is connected to the mixer 26 via the coupling capacitor 96.

If the tuner is constructed as described above, the varactor diode 52 is biased in the reverse direction. As a result, the capacitance of the capacitance diode changes 52 depending on the voltage applied to the power supply input VT and the resonance frequency of the oscillating circuit consisting of the inductance 46, the capacitance diode 52 and the capacitor 54 changes accordingly. In addition, this resonance

20 · frequency by changing the distance between the inductances 46 and 56 finely adjusted. The oscillation signal flowing through the inductance 46 is over transmit the coupling inductance 62 to the diode 64.

The oscillator 20 contains the fixed capacitance 90 and therefore vibrates at a fixed frequency. The fine adjustment of the oscillation frequency is also carried out through Change in the distance between inductances 84 and 92 »The oscillation signal flowing through inductance 84 is transmitted via the coupling inductance 66 to the mixer 18 and at the same time via Coupling inductance 94 and capacitor 96 on mixer 26.

The present invention is not limited to the above

described embodiment limited and without deviation Numerous changes and modifications can be made to the spirit of the invention. Short said the essence of the invention is that by using a signal which is produced by mixing the output of the local oscillator with variable oscillation frequency with the output signal of the oscillator fixed frequency arises, an input RF signal is converted into a first IF signal, which is a has a fixed frequency that is higher than that of the usual IF signal.

Claims (1)

BLUMBACH · WESER · BERGEN · KRAMER ZWIRNER HOFFMANN 31 506! PATENT LAWYERS IN MUNICH AND WIESBADEN Patentconsult Radeckestraüe 43 8000 Munich 60 Teleton (089) 883603/883604 Telex 05-212313 Telegrams Patentconsult
Patentconsult Sonnenberger Straße 43 6200 Wiesbaden Telephone (06121) 562943/561998 Telex 04-186237 Telegrams Patentconsult TOKYO SHIBÄÜRA DENKI 81/87116 KABUSHIKI KAISHA Pf / sa Horikawa-cho, Saiwai-ku
Kawasaki-shi, Japan tuner Claims Tuner with ^v a signal input to which a high-frequency signal is applied,
a first oscillator with variable oscillation frequency, a second oscillator with a fixed oscillation frequency, a first frequency converter for converting the input high frequency signal into a first intermediate frequency signal as a function of the output signal of the first oscillator, this first intermediate frequency signal being a fixed one
Frequency has a second frequency converter for converting the output signal of the first frequency converter into a second intermediate frequency signal using the output signal of the second oscillator, this second intermediate frequency signal having a fixed frequency which is lower than
the frequency of the first intermediate frequency signal, '' Munich: R. Kramer Dipl.-Ing. · W. Weser Dlpl.-Phys. Dr. rer. nat. . E. Hoffmann Dlpl.-Ing.
Wiesbaden: PG Blumbach Dlpl.-Ing. . P. Bergen Prof. Dr. Jur.Dlpl.-Ing., Pat.-Ass., Pat.-Anw. until 1979. G. Zwirner Dlpl.-Ins. Dlpl.-W.-Ing. characterized in that the oscillation frequency of the second oscillator (20) is lower than the lowest oscillation frequency of the first oscillator (16), the output signals of the first and second oscillators (16 and 20) are superimposed in a mixer (18) will and the output signal of the mixer (18) is fed to the first frequency converter (14, 22). 2. Tuner according to claim 1, characterized in that the first frequency converter has a mixer (14) contains whose first or second input to the signal input (10) or the output of the mixer (18) is connected and which generates signals, the frequencies of which are the sum and the difference of the frequencies of the first and second input signals, as well as contains a filter (22) which is connected to the output of the mixer (14) and serves to filter out only the first intermediate frequency signal, and in that
the second frequency converter contains a mixer (26) whose first or second input is connected to the filter (22) or the second oscillator (20) and which generates signals, the frequencies of which are the sum and the difference of the frequencies of the first and second input signals, and contains a filter (28) which is connected to the output of the mixer (26) and serves to filter out only the second intermediate frequency signal. 3. Tuner according to claim 2, characterized in that the filter in the first frequency converter is an acoustic Surface wave filter is. 4. Tuner according to claim 1 or 2, characterized in that that the signal input (10) via a high-frequency amplifier (12) to the first frequency converter (14, 22) and the first frequency converter (14, 22) via an intermediate frequency amplifier (24) is connected to the second frequency converter (26, 28).