JPS60201749A - Up-down tuner - Google Patents

Abstract

PURPOSE:To improve the cross modulation distortions and also to prevent the output of a local oscillator from leaking out to an input terminal, by providing a signal level setting means between an input BPF and the 1st mixer. CONSTITUTION:A wide band signal supplied to an input terminal 1 is converted into a signal having a frequency higher than a reception frequency by the 1st mixer 3 and then converted into a prescribed frequency by the 2nd mixer 8. For an up-down tuner having such constitution as mentioned above, a signal level setting means 20 is provided between an input BPF2 and the mixer 3. This means 20 consists of an amplifier circuit 21 and an attenuator 22 and controls an input signal to an appropriate level to output it in consideration of the cross modulation distortion and the noise exponent. While the amplifier 21 prevents the leakage of the output of the mixer 3 to the input side to prevent back talk.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to up-down tuners, and particularly to an up-down tuner that reduces backtalk and reduces noise figure.

[Technical background of the invention and its problems]

Generally, a so-called double-superheterodia system using two mixers is used as a tuning means for a receiver used in a CATV or the like that transmits signals of multiple channels. As this double super chill rodine method, there is a tuning method known as an up-down tuner in which a first mixer raises the frequency to a predetermined frequency and a second mixer lowers the frequency to a desired frequency. The up-down chain is a tuning method often used in CATV equal pressure because it can receive signals over a wide band, such as the VHF band and the UHF band, with one tuning circuit without switching the band. Since up-down tuners receive multi-channel signals, the first mixer converts the received signal to a higher frequency once, but at this time, the output of the local oscillator leaks to the input side of the cheese, causing so-called backtalk. .

Moreover, this also causes the problem of deterioration of the noise figure. FIG. 1 is a circuit diagram showing a conventional up-down cheese. via the first mixer 3.

The output from the first local oscillator 4 is added to the first mixer 3, which converts the input signal to a high frequency and converts the input signal into a first local oscillator.
obtain an intermediate frequency signal. This first intermediate frequency signal
A first bandpass filter 5 for the intermediate frequency, this first intermediate frequency wave amplifier 6, and a second bandpass filter 7.
is added to the second mixer 8 via. In the second mixer 8, the input signal converted to a high frequency by the first mixer is frequency-converted to a predetermined frequency by a second local oscillator 9. The converted signal is guided to an output terminal 11 via an output bandpass filter 10.

As mentioned above, the up/down tuner receives signals over a wide band without sub-switching.Usually, in consideration of cross-modulation and intermodulation, the first mixer 3 is equipped with a signal as shown in the second A mixer using a diode as a mixer element is used. A mixer constructed of diodes as described above has advantages in terms of cross-modulation and intermodulation, but it also has problems.

In addition, when up-down cheese is used for CATV,
Signals other than the reception channel are converted by the first mixer 3, and the converted unnecessary signals are reflected by the first bandpass filter, and a backtalk filter is usually provided to attenuate so-called backtalk that appears on the input terminal side. . Therefore, a filter is required to remove backtalk.

In addition, a filter is also required to prevent the output of the first local oscillator 4 from leaking to the input terminal 1.

In this way, in conventional up-down tuners,
The noise figure performance is insufficient9, and a filter with complex characteristics is required to prevent backtalk and prevent the output of the local oscillator from leaking to the input terminal, and the above manual bandpass filter with backtalk filter BP 2 had to have a complicated configuration as shown in FIG.

[Purpose of the invention]

This invention was made in view of the above points, and improves performance such as noise figure, backtalk, and leakage to the input side of the local oscillator, and also provides an up-down cheese with a simple circuit configuration. The purpose is to provide.

[Summary of the invention]

In this invention, in a so-called up-down tuner that receives a wideband signal, the first mixer converts it to a higher frequency and the second mixer converts the frequency to a predetermined receiving frequency. A signal level setting means is provided between the first mixer, and an up-down tuner with excellent characteristics for preventing the noise index, intermodulation distortion, and backtalk is provided with a simple circuit configuration.

[Embodiments of the invention]

Hereinafter, with reference to the drawings, an up-down team according to the present invention will be explained.
An example in which this embodiment is applied to CATV will be described in detail.

FIG. 4 shows an embodiment of the up-down tuner according to the present invention, which is the same as the up-down tuner shown in FIG. 1, although the circuit configuration is different in that a level setting means is added. The same reference numerals are given to the functional parts, and the explanation thereof will be omitted.

In FIG. 4, a CATv signal input to an input terminal 1 is filtered by an input bandpass filter 2 to remove unnecessary signals, and is applied to a signal level setting means 20.

This signal level adjusting means includes an amplifier circuit 21 and an attenuator n, and obtains a system-required signal level at the output of the signal level adjusting means.

Here, the buttons and take-off index will be explained for comparison with conventional up-down tuners. The noise figure of the cheese according to this invention is NFt, and the noise figure of the conventional cheese is NFt.
l. If the noise figure of a single amplifier is NF and its gain is 0, then.

In addition, in the above equation, the gain OA of the amplifier circuit 21 is
The larger the tuner noise figure NFtF
However, since the mixer uses a diode, which is a non-linear element, the tuner as a whole suffers from cross-modulation and intermodulation distortion, making it impractical. Toe 9
If the gain of the amplifier circuit 21 is increased too much, cross-modulation distortion becomes noticeable and the noise figure of the tuner as a whole deteriorates.

Therefore, in consideration of improving the noise figure and cross-modulation distortion, the signal level is set by the amplifier circuit 21 and the attenuator n.
It is necessary to do this.

FIG. 5 is a characteristic diagram showing the relationship between the gain of the amplifier circuit 21 and the noise figure in the embodiment of the up-down tuner according to the present invention.
1 and attenuator n are shown. In FIG. 5, the characteristic curve (A) has a gain of the amplifier circuit 21 of 1 OdB, an attenuation amount of the attenuator of 2 dB, and a characteristic curve (B) +d
:The gain of the amplifier circuit 21 is 8 dB, the attenuation f1N of the attenuator is 4 dB, and the characteristic curve (C) shows the characteristics when the gain of the amplifier circuit 21 is 6 dB and the attenuation amount of the attenuator is 6 dB. As can be seen from the characteristic diagram shown in FIG. 4, it can be seen that the larger the gain 14 of the amplifier circuit 21, the lower the noise figure, which is advantageous in terms of the noise figure. This means that
In the above equation, if the gain GA of the amplifier circuit 21 is increased, the noise figure is improved, but if the gain of the amplifier circuit 21 is increased, the cross-modulation characteristics and intermodulation characteristics as a cheese deteriorate.

FIG. 6 shows the gains of the amplifier circuit 21 and attenuator B corresponding to the characteristic surfaces mh, B, and c in FIG. 5 described above.

It is a characteristic diagram showing characteristics corresponding to the amount of attenuation, in which the horizontal axis shows frequency and the vertical axis shows cross-modulation degree. As can be seen from FIG. 6, the larger the gain of the amplifier circuit ρ, the worse it is with respect to cross-modulation distortion. Therefore, in this embodiment, the signal level setting means is added to the amplifier circuit 21. The amplifier circuit 21 is configured with an attenuator n and sets the level of the signal input to the first mixer 3. In this way, the amplifier circuit 21 contributes to improving the noise figure. Since the output impedance is large, the output of the first mixer 3 is prevented from being returned to the input bandpass filter 2 side. That is, the amplifier circuit 21 of the level setting means
contributes to the prevention of backtalk in addition to the prevention of noise figure characteristics.

Generally, in a double superheterodyne tuner for CATU, in order to remove pack talk signals, a high-pass filter section as shown in FIG.
Low pass filter section, variable pack talk filter section BP
However, according to the present invention, reback talk is removed by adding a signal level setting means.
The configuration of the input bandpass filter can be simple.

To address this problem, consideration must be given to noise figure, backtalk, and prevention of leakage of the output of the first mixer to the input end.

Here, in order to compare the characteristics of the conventional up-down tuner and the up-down tuner according to the present invention, the conventional up-down tuner having no signal level setting means is compared with the up-down tuner according to the present invention.
Amplifying circuit 21 and attenuator 21 with level setting means
The results of an experiment on the characteristics of tuner C, in which the backtalk filter circuit is removed and an amplifier circuit 21 is provided in that part, are shown below.As can be seen from the results of this experiment, a signal level setting means was provided The examples of up-down tuners B and C according to this invention are superior to conventional ones in all aspects of noise figure, backtalk, and leakage of local oscillator output to the input end. 7 shows the circuit configuration for the C cheese of the above tuner, and the input bandpass filter 2 of the conventional up-down tuner shown in FIG. 3 above.
Signal level setting means 2 with a simple filter configuration compared to the configuration of
By simply providing 1, it is possible to improve the noise figure, backtalk, and leakage of the local oscillator output to the input end.

Further, as a characteristic of the cheese, so-called isolation is required, which indicates the level of the signal leaked to the input side when a signal is applied to the output side of the first mixer 3. This isolation depends on the operation of the signal level setting means 21, and FIG. 8 shows the isolation characteristics of the amplifier circuit 21 constituting the signal level setting means side. As shown in Figure 8, at practical frequencies, the value is approximately constant -20 dB.
It should show the isolation of , and satisfy the isolation and broadband characteristics.

FIG. 9 is a circuit diagram showing an example of the amplifier circuit 21 that satisfies the isolation characteristics and broadband characteristics as described above, in which the output of the input bandpass filter 2 is applied from the input terminal IN to the emitter-grounded transistor Q1. , further via the base-grounded transistor Q2, and then the attenuator A
It is output to the output terminal OUT via TT. In addition, the resistance R
1. The capacitor C1 is a feedback element, and by making it an isolation and feedback type with this configuration, it is possible to set a gain that improves broadband characteristics and a good noise figure, and to set an appropriate gain for cross modulation. will be done.

Further, the attenuator n constituting the signal level setting means may be of a variable type as shown in FIG. 10, and the pins Pi and P2 may be of the form as shown in FIG. The amount of attenuation may be controlled by . As a result, even if CAT with a wide reception band
The present invention provides an up-down tuner suitable for double super-heterodyne systems such as V.

[Effects of the Invention] As described above, the present invention has excellent performance against noise figure backtalk, cross-modulation distortion, leakage of local oscillator output to the input terminal, etc. The chips can be provided with a simple circuit configuration.

Note that the up/down tuner according to the present invention is applicable to CATV.
However, it is generally widely applied when wideband reception is required.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional up-down tuner, Fig. 2 is a circuit diagram showing a general mixer, and Fig. 3 is a circuit diagram showing an input bandpass filter of a conventional up-down tuner. , Fig. 4 is a circuit diagram showing an embodiment of the up-down tuner according to the present invention, and Figs. 7, 9, and 10 are circuit diagrams showing the circuit portions 4' and 11 of the present invention. 1...Input terminal, 2...Input bandpass filter,
3... first mixer, 4... first local oscillator, 5
...first band pass filter, 7...second band pass filter. 8...Second mixer, 9...Second local oscillator, addition...Signal level setting means. Figure 1 Figure 2 Figure 3 R @ Figure 4 Figure 5 Frequency Figure 8 Frequency Figure 7 Figure 9 Figure 1 Formula % 2, Name of the invention ν Tsubugunchi 1-3, Supplementary information 1 1 ``J matter which relationship Special; 21 Applicant (307) Toshiba Corporation 4, Agent 〒105 1978 (r (3 Month 26EI (Shipping [1) 6, subject of amendment 111J, simple drawing of 111 store'cK iJJ light column 7, capture O) Contents and more

Claims (1)

[Claims] An input bandpass filter has an output terminal that extracts a predetermined frequency band signal from the received signal applied to the input terminal and outputs it; a signal level setting means for setting the optimum level of the determined signal; a first mixer for converting the output signal of the signal level setting means into a high frequency by a mixing action with a first local oscillator; A first Nohant Hass filter performs a band-pass action on the output of the first mixer; An up-down tuner comprising at least a second mixer that converts the converted signal into a predetermined reception frequency.