JPH11284537A - Tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve phase noise over the entire band and to reduce fixed deterioration of a system, especially when receiving a digital broadcasting signal. SOLUTION: This tuner divides an inputted high frequency signal into plural (three) passbands at a band changeover switch 113 to enable output, provides each passband with a variable filtering means and a frequency converting means, and outputs an IF signal that undergoes frequency conversion, into a prescribed intermediate frequency(IF). The respective circuit form of three local oscillators 118, 123 and 128 which constitute plural frequency converting means (117 and 118), (122 and 123) and (127 and 128) provided in each passband are an unbalanced oscillator circuit in a UHF band, an unbalanced or balanced oscillator circuit in a VHF high band, and a balanced oscillator circuit in a VHF low band. As result, it is possible to secure an oscillation range in the VHF band and to improve phase noise in the UHF band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner suitable for use in a digital CATV receiver or a terrestrial digital TV receiver used for receiving digital broadcast signals.

[0002]

2. Description of the Related Art With the recent digitalization and multimedia, in the field of broadcasting, not only the current broadcasting of radio systems such as TVs, but also the integration of broadcasting and communication has been carried out.
Cable broadcasting such as TV has also attracted attention.

[0003] By the way, in a single superheterodyne tuner of all band reception currently used in most TV broadcasting receivers, a VHF low band,
In the case of three bands, the HF high band and the UHF band, the block configuration has three local oscillators. Also, VHF band,
In the case of two bands in the UHF band, the block configuration has two local oscillators. Therefore, the number of bands and the number of local oscillators are the same.

Recently, as a tuner used for receiving digital broadcasting, use of a single superheterodyne tuner including one set of a mixer and one local oscillator for each band has been reconsidered. This is because the circuit configuration is simpler and more cost effective than that of a double superheterodyne tuner.

In general, as a single superheterodyne tuner currently used, a tuner employed in a TV receiver is well known.

FIG. 3 shows a configuration example of a conventional single superheterodyne type TV tuner, and FIG. 4 shows a specific circuit configuration of a local oscillator used in the tuner of FIG. However, for simplicity, the description of the configuration will focus on one of the three bands.

As shown in FIG. 3, a TV tuner includes:
An input terminal 210 for receiving an input signal is provided, and the input terminal 210 is supplied with a high-frequency signal (RF signal) received by a receiving antenna (not shown). The RF signal input to the input terminal 210 includes a low-pass filter (LPF) 211 and a high-pass filter (HP
F) After passing through only a predetermined frequency band by 212, it is supplied to the switch 213.

The switch 213 converts the input RF signal into 3
Band (UHF band, VHF high band, VHF low band)
Are switched according to the desired band, and are output to the corresponding variable trunking filters 214, 219, 224, respectively. For example, if the switch 213 switches to the UHF band based on the input terminal a, the input R
The F signal is supplied to a variable tracking filter 214 whose band is controlled by a control voltage to a local oscillator, and a predetermined band is limited by the variable tracking filter 214 and supplied to an RF amplifier 215.

The RF amplifier 215 adjusts the level so that the signal is amplified at a level based on the gain control signal, and supplies the amplified signal to a variable tracking filter 216 at the subsequent stage. The variable tracking filter 216 further limits the band of the input signal and outputs the signal. This output signal is then provided to mixer 217.

The mixer 217 converts an input signal from the variable tracking filter 216 into an intermediate frequency signal (IF signal) using the oscillation frequency from the local oscillator 218 and outputs the intermediate frequency signal. This IF signal is thereafter limited to a predetermined IF band by being applied to a band-pass filter (hereinafter referred to as BPF) 229, further amplified by an IF amplifier 230, further band-limited by a BPF 231 and then to an IF amplifier 23.
It is amplified by 2 and output from the output terminal 235.

The VHF high band and the VHF low band are also converted into IF signals by respective circuits (219 to 223) and (224 to 228), then band-limited by BPF229 and IF amplifier.
After amplification by 230 and band limitation by BPF231, IF amplifier 232
And is output from the output terminal 235.

The local oscillators 218, 223,
For 228, a voltage controlled oscillator (VCO) is used. P
The LL circuit 233 includes at least a phase comparator, a low-pass filter, and a reference oscillator.
The oscillation frequency of each oscillator is controlled by generating a control signal by comparing the phases of the oscillation frequency signals of 8, 223 and 228 and the reference oscillation frequency signal, and applying the control signal to the local oscillators 218, 223 and 228. Things.

In the circuit shown in FIG. 3, the frequency conversion unit indicated by reference numeral 234 is integrated into an IC to reduce the size and power consumption. The IC 234 includes circuits of mixers 217, 222, 227, local oscillators 218, 223, 228, and an IF amplifier 230.

Here, the local oscillators 218, 223, 228
The circuit format used in the above is a balanced oscillation circuit for all the bands, which is suitable for IC.

FIG. 4A shows a main part of a balanced oscillation circuit used for the local oscillator 218 in the UHF band. It has two transistors Q11 and Q12. The emitters of Q11 and Q12 are connected to reference potential points via constant current sources I11 and I12. The voltage from DC power supply E11 is applied to transistors Q11 and Q12 via resistors R11 and R12. Supply to each base of Q12
The control voltage from the PLL circuit is input to the input terminal IN connected to each base of the transistors 11 and Q12, and the oscillation output is taken out from the output terminal OUT connected to the emitters of the transistors Q11 and Q12.

FIG. 4B shows a main part of a balanced oscillation circuit used for the local oscillators 223 and 228 in the VHF high band and the VHF low band. Two transistors Q13, Q14
The emitters of the transistors Q13 and Q14 are commonly connected, and the collectors of the transistors Q13 and Q14 are connected to a resistor R
The common emitter is connected to a reference potential point via a constant current source I13, and the bases of the transistors Q13 and Q14 are connected to a DC power supply E12 via resistors R15 and R16. Then, the base of the transistor Q13 is connected to the reference potential point via the capacitor C1, a control voltage from the PLL circuit is supplied to the input terminal IN connected to the base of the transistor Q14, and the output terminal OUT connected to the collector of the transistor Q13. More oscillation output is taken out.

However, the IC 23 used in the above-mentioned single superheterodyne tuner for TV is used.
4. The local oscillator in 4 is a balanced oscillation circuit, so the use of two transistors complicates the internal circuit. Therefore, the stray capacitance in the IC increases, and the stray capacitance due to the increase in external auxiliary circuits increases. In addition, the effect of thermal noise of the transistor itself also increases due to the increase in the number of elements, and the noise flow of the oscillator increases, so that the oscillation frequency increases. In particular, the phase noise of the oscillator tends to deteriorate.

For this reason, in the case of performing reception by digital transmission, which will become mainstream in the future, especially 64QAM, 256QA
In the case of a multi-level transmission mode such as M, 16VSB, 32VSB, or a transmission mode such as OFDM in which the transmission rate per wave is low but the number of carriers is large, whether the phase noise is good or bad depends on the entire receiving system. This is particularly problematic because it has a significant effect on fixation degradation.

[0019]

As described above, in the conventional tuner, the local oscillator uses a balanced oscillator circuit composed of two transistors.
Oscillation frequency increases due to an increase in stray capacitance inside
The phase noise of the oscillator in the HF band tends to be particularly deteriorated. Therefore, in the case of receiving a digital broadcast signal that will become mainstream in the future, there is a problem that the fixed deterioration of the entire receiving system is increased due to phase noise.

The present invention has been made in view of the above problems, and has as its object to provide a tuner capable of improving phase noise and, in particular, reducing fixed deterioration of a receiving system in digital transmission. It is.

[0021]

According to a first aspect of the present invention, there is provided a tuner including a plurality of frequency conversion means including a local oscillator and a mixer, wherein the circuit format of the plurality of local oscillators is an unbalanced oscillation circuit. And a balanced type oscillation circuit.

According to the configuration of the present invention, since an unbalanced oscillation circuit and a balanced oscillation circuit are appropriately combined and used, the circuit configuration is simplified and a high-performance tuner excellent in phase noise is provided. Can be realized.

According to a second aspect of the present invention, there is provided a tuner comprising: an input terminal to which a high-frequency signal is input; band switching means for dividing the high-frequency signal input to the input terminal into a plurality of pass bands and outputting the divided pass band; Frequency conversion means comprising a plurality of frequency conversion means comprising a voltage-controlled local oscillator and a mixer, corresponding to the plurality of pass bands, wherein each of the frequency conversion means is a high frequency switched by the band switching means. A plurality of frequency conversion means for mixing a signal and a local oscillation signal from the local oscillator corresponding thereto to generate an intermediate frequency signal, and disposed between the band switching means and the plurality of frequency conversion means, A plurality of variable filter means for limiting each of the plurality of passbands by a control voltage for controlling a local oscillator of the plurality of local oscillators. Circuit type of oscillator, wherein the oscillator circuit unbalanced, by comprising an oscillation circuit of the two forms of the balanced oscillator circuit.

According to the configuration of the present invention, since an unbalanced oscillation circuit and a balanced oscillation circuit are appropriately combined and used, a comparison is made between using a balanced oscillation circuit in all bands as in the conventional circuit. As a result, it is possible to provide a single superheterodyne tuner excellent in phase noise over all bands.

According to a third aspect of the present invention, in the tuner according to the second aspect, the plurality of pass bands include a VHF low band, a VHF
If there are three bands, HF high band and UHF band, VH
The local oscillator corresponding to the F low band is a balanced type, and the local oscillator corresponding to the VHF high band is a balanced type or an unbalanced type.
It is characterized in that the local oscillator corresponding to the UHF band is of an unbalanced type.

According to the present invention, in the case of a three-band configuration, the phase noise is deteriorated in the UHF band having a high oscillation frequency.
The problem can be solved by making the local oscillator in the UHF band an unbalanced oscillator. In the VHF low band, since the oscillation frequency is low, the adverse effect of the balanced local oscillator is small, and the deterioration of the phase noise is small. Therefore, the balanced local oscillator having a relatively easy oscillation range is provided. For the VHF high band, an unbalanced local oscillator is used if importance is placed on phase noise, and a balanced local oscillator is used if importance is placed on the oscillation range.

According to a fourth aspect of the present invention, in the tuner of the single superheterodyne system according to the second aspect, when the plurality of pass bands are two bands of a VHF band and a UHF band, a local area corresponding to the VHF band. It is characterized in that the oscillator is a balanced type and the local oscillator corresponding to the UHF band is an unbalanced type.

In the present invention, the UHF
By using a local oscillator in the band as an unbalanced oscillator and a local oscillator in the VHF band as a balanced oscillator, the same effect as in the case of a three-band configuration can be obtained.

[0029]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a single superheterodyne tuner according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a specific configuration of a local oscillator used in the tuner of FIG. ing. In the description of the configuration, one of the three bands is mainly described for simplification.

As shown in FIG. 1, an input terminal 110 for receiving an input signal is provided. The input terminal 110 has a high frequency signal (R) received by a receiving antenna (not shown).
F signal). Input terminal 210
The RF signal input to is passed through only a predetermined frequency band by the LPF 111 and the HPF 112, and then supplied to a band switch 113 serving as band switching means.

The band changeover switch 113 is switchable in accordance with a desired band among three bands (UHF band, VHF high band, VHF low band), and switches an input RF signal to three switching output points. By connecting to any of a, b, and c, the signal is output to any of the variable trunking filters 114, 119, and 124 as the variable filter means connected to each output point a, b, and c. For example, UHF corresponding to the input terminal a by the switch 113
If you switch to the band, the input RF signal is
The signal is supplied to a variable tracking filter 114, which is a variable filter means whose band is controlled by a control voltage applied to the local oscillator, and is limited to a predetermined band by the variable tracking filter 114 and supplied to an RF amplifier 115.

The RF amplifier 115 adjusts the level so as to amplify the signal at a level based on the control voltage of the local oscillator, and supplies the amplified signal to the variable tracking filter 116 at the subsequent stage. The variable tracking filter 116 is a variable tracking filter 114
Similarly to the above, the band is controlled by the control voltage of the local oscillator.
The variable tracking filter 116 further limits the band of the input RF signal and outputs the signal. This output signal is then
It is provided to a mixer 117.

The mixer 117 converts the input signal from the variable tracking filter 116 into an intermediate frequency signal (IF signal) using the oscillation frequency from the local oscillator 118 and outputs the intermediate frequency signal (IF signal). The mixer 117 and the local oscillator 118 constitute frequency conversion means in the UHF band. The IF signal from the frequency conversion means is then limited to a predetermined IF band by being applied to a BPF 129, further amplified by an IF amplifier 130, band-limited by a BPF 131, amplified by an IF amplifier 132, and output to an output terminal 135. Output from

The VHF high band and VHF low band are also converted into IF signals by respective circuits (119 to 123) and (124 to 128). The mixer 122 and the local oscillator 123 have VH
The frequency converting means in the F high band is constituted, and the mixer 127
And the local oscillator 128 constitute frequency conversion means in the VHF low band. The frequency-converted IF signal is represented by B
Band limit by PF129, amplification by IF amplifier 130, BPF13
After the band is limited by 1, the signal is amplified by IF amplifier 132 and output terminal 13
Output from 5.

The local oscillators 118, 123,
A voltage-controlled local oscillator (VCO) is used as 128. The PLL circuit 133 includes at least a phase comparator, a low-pass filter, and a reference oscillator, and generates a control signal by comparing the phases of the oscillation frequency signals of the local oscillators 118, 123, and 128 with the reference oscillation frequency signal. By giving the control signal to the local oscillators 118, 123, and 128, the oscillation frequency of each oscillator is controlled.

In the circuit shown in FIG. 1, the frequency conversion unit indicated by reference numeral 134 is integrated into an IC to reduce the size and power consumption.
The IC 134 includes circuits of mixers 117, 122, and 127, local oscillators 118, 123, and 128, and an IF amplifier 130.

Here, the local oscillators 118, 123, 128
The UHF band local oscillator 118 employs an unbalanced oscillation circuit, the VHF high band employs an unbalanced or balanced oscillation circuit, and the VHF low band employs a balanced oscillation circuit. ing.

In the case of the above three-band configuration, in the UHF band having a high oscillation frequency, the local oscillator 118 is replaced with an unbalanced oscillation circuit to improve the phase noise. VHF with low oscillation frequency
The low-band local oscillator 128 is a balanced oscillation circuit that can secure an oscillation range. In the VHF high band, a balanced or unbalanced oscillation circuit is selected, such as an unbalanced oscillation circuit if the phase noise is important and a balanced oscillation circuit if the oscillation range is important.

FIG. 2A shows a UHF band (or a VHF high band).
2 shows a main part of an unbalanced oscillation circuit used for the local oscillator 118 (or 123). It has one transistor Q1 and has resistors R1 and R2 between a power supply line VCC and a reference potential point.
, Diodes D1 and D2 are connected in series, and resistors R1 and D2 are connected in series.
The voltage at the connection point of R2 is supplied to the base of the transistor Q1, the constant current source I1 is connected between the emitter of Q1 and the reference potential point, and the input terminal IN is connected to the base of the transistor Q1 to control the voltage from the PLL circuit. And an oscillation output is taken out from an output terminal OUT connected to the emitter of the transistor Q1.

FIG. 2B shows a main part of a balanced oscillation circuit used for the local oscillator 128 (or 123) in the VHF low band (or VHF low band). Two transistors Q2
, Q3, the emitters of the transistors Q2 and Q3 are connected in common, the collectors of the transistors Q2 and Q3 are connected to the power supply line VCC through the resistors R3 and R4, and the common emitter is connected through the constant current source I2. To the reference potential point, and connect the bases of the transistors Q2 and Q3 to the resistors R5 and R5.
6, the base of the transistor Q2 is connected to the reference potential point via the capacitor C1, and the PLL is connected to the input terminal IN connected to the base of the transistor Q3.
A control voltage is supplied from the circuit, and an oscillation output is taken out from an output terminal OUT connected to the collector of the transistor Q2.

According to the above-described embodiment, the local oscillator 118 for UHF used for the IC 134 of the single superheterodyne tuner is an unbalanced oscillation circuit. It becomes simpler, the stray capacitance in the IC is reduced, the stray capacitance is reduced due to the reduction of external auxiliary circuits, the oscillation intensity is maintained by reducing the pattern inductance, and the number of elements is also reduced due to the thermal noise of the transistor itself. As a result, the phase noise of the oscillator in the UHF band where the oscillation frequency is high can be satisfactorily improved.

Therefore, in the case of receiving digital broadcast signals which will become mainstream in the future, especially 64QAM, 256QA
In the case of multi-level transmission modes such as M, 16VSB, and 32VSB, and transmission modes such as OFDM, in which the transmission rate per wave is low but the number of carriers is large, the overall reception system caused by the quality of the phase noise is increased. It is possible to obtain the effect of reducing the fixing deterioration.

In the embodiment described above,
In the tuner configuration shown in FIG. 1, a three-band system capable of switching three pass bands has been described.
The present invention is not limited to this, and may be configured as a two-band system. In the case of a two-band configuration, the local oscillator in the UHF band is connected to an unbalanced oscillation circuit by VHF.
The local oscillator of the band is a balanced oscillation circuit. Again,
The same effects as in the above embodiment can be obtained.

In the above embodiment, a single superheterodyne tuner has been described.
The present invention can also be applied to a tunable superheterodyne tuner.

[0045]

As described above, according to the present invention, in a tuner having a plurality of frequency conversion means, by appropriately using an unbalanced local oscillator, the circuit configuration is simplified and the phase noise is improved. can do. In particular, by appropriately combining a balanced oscillation circuit and an unbalanced oscillation circuit with a local oscillator of a frequency conversion means in a tuner capable of switching a plurality of bands, for example, a UHF band, a VH
Good phase noise performance can be provided in all bands of the F band. The required oscillation range in the VHF band can be obtained.
The phase noise in the HF band can also be improved, and it is possible to reduce the fixed deterioration of the system, especially when receiving a digital broadcast signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a tuner according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration example of a local oscillator in FIG.

FIG. 3 is a block diagram showing a configuration of a tuner of a conventional example.

FIG. 4 is a block diagram showing a configuration example of a local oscillator in FIG. 3;

[Explanation of symbols]

110: RF signal input terminal 113: Band change switch (band change means) 114, 116, 119, 121, 124, 126 ... Variable tracking filter (variable filter means) 117, 122, 127 ... Mixer 118, 123, 128 ... local oscillators 129, 131 ... BPF 133 ... PLL circuits 135 ... output terminals

Claims (4)

[Claims] 1. A tuner provided with a plurality of frequency conversion means including a local oscillator and a mixer, wherein the plurality of local oscillators have two types of circuit types: an unbalanced oscillation circuit and a balanced oscillation circuit. A tuner comprising an oscillation circuit. 2. An input terminal to which a high-frequency signal is input, band switching means for dividing the high-frequency signal input to the input terminal into a plurality of passbands and outputting the divided passband, a voltage-controlled local oscillator, and a mixer. Frequency conversion means comprising a plurality of frequency converters corresponding to the plurality of passbands, wherein each of the frequency conversion means is a high-frequency signal switched by the band switching means and A plurality of frequency conversion means for mixing a local oscillation signal from a local oscillator to generate an intermediate frequency signal; and a control arranged between the band switching means and the plurality of frequency conversion means for controlling the local oscillator. A plurality of variable filter means for limiting each of the plurality of passbands by a voltage, and a tuner of a single superheterodyne system comprising: The tuner is characterized in that the plurality of local oscillators include two types of oscillation circuits: an unbalanced oscillation circuit and a balanced oscillation circuit. 3. The method according to claim 2, wherein the plurality of pass bands are a VHF low band,
If there are three bands, VHF high band and UHF band, V
The local oscillator corresponding to the HF low band is balanced and VHF
3. The tuner according to claim 2, wherein the local oscillator corresponding to the high band is a balanced type or an unbalanced type, and the local oscillator corresponding to the UHF band is an unbalanced type. 4. The method according to claim 1, wherein the plurality of pass bands are VHF band, UH band.
3. The tuner according to claim 2, wherein when the two bands are the F band, the local oscillator corresponding to the VHF band is of a balanced type, and the local oscillator corresponding to the UHF band is of an unbalanced type.