JP2699717B2 - Tuning device for double conversion receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a BS for receiving multi-channel video / audio amplitude information of the FM-FDM system.
The present invention relates to a channel selection device for a double conversion receiver used for a (satellite broadcast) receiver.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration of a channel selection device for a single conversion receiver used in a conventional BS broadcast receiver.

[0005] In FIG. 5, reference numeral 1 denotes a mixer for frequency-converting an RF (high frequency) signal of a BS broadcast wave into an intermediate frequency signal IF ₂ and outputting the intermediate frequency signal IF ₂ . 3 is a FM (frequency modulation) detector for outputting a demodulated signal, 9a is a local oscillator, the local oscillation signal Lo ₃ to a VCO (voltage-controlled oscillator) supplied to the mixer 1, 10 is the reference frequency oscillator, 11 Is a reference frequency divider, 13 is a fixed frequency divider, 14 is a comparative frequency divider, 15 is a phase comparator, 16 is a loop filter, 17 is a frequency division ratio controller,
Reference numeral 18 denotes an AFC circuit, and 19 denotes an arithmetic unit.

The operation in this configuration will be described.
Mixer 1 outputs the desired channel in the RF signal is converted by a local oscillation signal Lo ₃ into an intermediate frequency signal IF _2. F
The M detector 3 configures a PLL so as to synchronize the phase with the intermediate frequency signal IF _2, and sends the amplitude information signal to an input terminal of a VCO (voltage controlled oscillator), that is, an output terminal of the loop filter 16. The frequency of the local oscillation signal Lo ₃ changes according to channel selection, and the oscillation frequency corresponding to each channel is transmitted from the VCO 9a by a known control voltage. In the BS broadcasting band, the frequency variable range of the VCO 9a is 268.52 MHz.

The output signal of the reference frequency oscillator 10 is frequency-divided by the reference frequency divider 11 to obtain a phase comparison reference frequency signal. V
The output signal from the CO 9a is several tens MH by the fixed frequency divider 13.
The frequency is divided by z and input to the comparison frequency divider 14. Comparison divider 1
4 can be set arbitrarily, and this setting is made as a pre-registered dividing ratio based on the channel selection control signal.
And its output signal becomes the phase comparison frequency.
This frequency division ratio is a value such that the output frequency of the comparison frequency divider 14 becomes substantially equal to the phase comparison reference frequency. The phase comparison reference frequency signal and the phase comparison frequency signal are input to the phase comparator 15 to detect how much the phase comparison frequency is shifted in the positive or negative direction with respect to the phase comparison reference frequency. A control voltage into a DC voltage the phase shift by the loop filter 16 is supplied to VCO9a setting the local oscillation signal Lo ₃ to a predetermined frequency. The frequency variation of VCO9a are working to frequency stability of the intermediate frequency signal IF ₃ by adjusting the frequency of the local oscillation signal Lo ₃ by AFC (Automatic Frequency Control) from affecting the demodulation characteristics of the FM detector 3 . AFC circuit 18 as shown in FIG. 6, to set the reference level to the output voltage with respect to the center frequency of the intermediate frequency signal IF ₂ (402.78MHz) advance, AFC signal by detecting a deviation of the output voltage to the reference level and then, the intermediate frequency signal IF ₂ is adjusted local oscillation signal Lo ₃ so as to 402.278MHz by adjusting the frequency division ratio of a comparison frequency divider 14 by the AFC signal. Such a relatively narrow band VCO 9a is easy to realize, and the oscillation frequency with respect to the control voltage is also excellent in linearity.

In a single conversion system frequently used in BS broadcasting, for example, when a desired channel is selected from 50 channels in a multi-channel BS system, image interference appearing on the opposite side to a desired sideband generated by a mixer. Occurs, which has an adverse effect on the reception characteristics. In this case, a double-conversion receiver that converts the RF signal to a high-frequency intermediate frequency signal to eliminate image interference and further converts the RF signal to a low-frequency intermediate frequency signal to obtain desired selection characteristics is advantageous in practical use. is there.

FIG. 7 shows a configuration of a channel selection device for a double conversion receiver. In this tuning apparatus for a double conversion receiver, frequency conversion is performed twice for the configuration shown in FIG. 5, and in FIG. 7, reference numeral 2 denotes a second mixer,
Reference numeral 9 denotes a fixed frequency oscillator serving as a second local oscillator.
Other configurations are the same as those of the conventional single conversion system shown in FIG.

The operation of this configuration will be described below.
The mixer 1 is frequency-converted into an intermediate frequency signal IF ₁ and channel selection by the local oscillation signal Lo ₁ of the desired channel from among RF signals. The mixer 2 is frequency-converted into an intermediate frequency signal IF ₂ an intermediate frequency signal IF ₁ by local oscillation signal Lo _2. FM detector 3 demodulates the intermediate frequency signal IF ₂ to the original amplitude information. Other operations are the same as those of the conventional single conversion method shown in FIG.

FIG. 8 shows the relation between the frequency band and the local oscillation signal of each channel selection in the channel selection device for a double conversion receiver.

[0010] In FIG. 8, fRF is the input frequency of the RF signal, Flo1 the frequency of the local oscillation signal Lo _1, fLO2 are respectively the frequency of the local oscillation signal Lo _2. VCO4
Is a wide band of 1879.64 MHz to correspond to channel 1 to channel 50.

[0011]

When the local oscillation signal of the VCO 4 has a wide band, it is difficult to obtain an oscillation frequency characteristic linearly proportional to the control voltage as shown in FIG. In order to use such a non-linear VCO 4 for a channel selection device for a double-conversion receiver, the oscillation frequency of the VCO 4 required for channel selection of a desired channel must be finely adjusted with a control voltage. Further, since the loop gain characteristic of the loop filter 16a is designed by setting certain conditions, the loop gain is not constant in the PLL using the non-linear VCO4. Here, a method of switching the loop gain characteristic for each channel in accordance with the oscillation characteristic of the VCO 4 can be considered, but this is technically impossible.

A common problem of the single conversion system used frequently for BS broadcasting and the double conversion system in the multi-channel BS system is that a local oscillation unit used for channel selection is controlled by a PLL loop. In this case, the intermediate frequency signal IF ₂ And a double loop controlled by the center frequency stabilized AFC. If the double loop is controlled in real time, the loops are controlled in mutually opposite directions, so that the loop cannot be stabilized. The PLL loop is controlled in real time, and the AFC loop is stabilized by intermittent control.

Therefore, in such a channel selecting device for a double conversion receiver, a wideband VCO cannot be easily realized, and a local oscillation signal is set in a double loop.
There is a disadvantage that the signal processing scale increases.

The present invention solves this problem, and can easily realize a wide-band VCO constituting a local oscillation section, can further realize the setting of a local oscillation signal by a single loop, and can reduce the signal processing scale. An object of the present invention is to provide an excellent channel selection device for a double conversion receiver.

[0015]

In order to achieve this object, a tuning apparatus for a double-conversion receiver according to the present invention provides a local oscillation signal for converting a high-frequency signal into a first intermediate frequency signal. And a second local oscillator for converting the first intermediate frequency signal into a second intermediate frequency signal.
And an FM detection circuit for obtaining an FM detection signal from the second intermediate frequency signal.
In the local oscillation section, the control voltage for the local oscillation signal is read from the oscillation frequency characteristic of the AFC and stored as a parallel input code of a D / A (digital / analog) converter. An input code is output to be used as a parallel input of the D / A converter, and the oscillation frequency of the AFC is set by the output voltage of the D / A converter.

Further, in addition to this configuration, a reference level is set for the output voltage with respect to the center frequency of the second intermediate frequency signal based on the FM detection characteristic, and the AFC is determined by the difference between this reference level and the FM detection output value. Generate AF signal
By changing the parallel input code of the D / A converter with the C signal, the oscillation frequency of the AFC is changed, and the second intermediate frequency signal is automatically adjusted.

In addition to the above configuration, the second local oscillation section generates a phase comparison reference frequency,
The output of the AFC in the extremely narrow band is divided by the comparison divider to obtain a phase comparison frequency, the phase comparison frequency is compared with the phase comparison frequency, and the control voltage of the AFC is passed through a loop filter. Oscillator is generated and F
A reference level is set to the output voltage with respect to the center frequency of the second intermediate frequency signal based on the M detection characteristic, and an AFC signal is generated based on a difference between the reference level and the FM detection output value. The intermediate frequency is automatically adjusted by changing the frequency division ratio of the filter to change the oscillation frequency of the AFC.

[0018]

Therefore, the tuning apparatus for a double conversion receiver according to the present invention reads the control voltage of the VCO for the local oscillation signal in the first local oscillation section from the oscillation frequency characteristic of the VCO, and executes the parallel operation of the D / A converter. It is stored as an input code, and the corresponding parallel input code is read out based on the channel selection information signal, and is input in parallel to the D / A converter.
Since the oscillation frequency of the VCO changes according to the output voltage of the / A converter, a wideband VCO constituting a local oscillation circuit can be easily realized.

Further, since the AFC loop for stabilizing the center frequency of the second intermediate frequency signal is fed back to the control system of the output code of the D / A converter, the setting of the local oscillation signal is realized by a single loop. And the signal processing scale is reduced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a tuning apparatus for a double conversion receiver according to the present invention will be described with reference to the drawings.

In FIGS. 1, 2 and 3, and in the text, the same components as those in FIGS. 5, 6, 7, 8, and 9 are denoted by the same reference numerals, and The detailed description in the text is omitted.

FIG. 1 shows the configuration of the first embodiment.
1, mixer and outputs the frequency-converted into an intermediate frequency signal IF ₁ of high frequency, 2 is a mixer for outputting the frequency-converted into an intermediate frequency signal IF ₂ of lower frequency. 3 is F
Reference numeral 4 denotes a MCO detector, 4 denotes a first local oscillator, a VCO for supplying the local oscillation signal Lo ₁ to the mixer 1, 5 a filter, 6 a D / A converter, 7 a D / A level. It is a controller. Reference numeral 9 denotes a second local oscillator, which is a fixed frequency oscillator that supplies a local oscillation signal Lo ₂ to the mixer 2.

Next, the operation of the configuration of the first embodiment will be described. The mixer 1 selects a desired channel from the RF signal,
And it outputs an intermediate frequency signal IF ₁ converted by supplying a local oscillation signal Lo _1. Also, the mixer 2 has an intermediate frequency signal IF
₁ is converted to the intermediate frequency signal IF ₂ by the local oscillation signal Lo ₂ .
Frequency conversion. The FM detector 3 outputs the intermediate frequency signal IF
₂ is demodulated to the original amplitude information.

Here, the VCO 4 has the same characteristics as in FIG. 9 and generates a control voltage of the VCO 4 by the D / A converter 6 and sends it out. The step voltage of the VCO 4 is determined by the relationship between the maximum value of the control voltage and the quantization number of the D / A converter 6, and a point where the output frequency changes greatly with respect to the control voltage change, for example, in FIG. It is determined in the range of the channel selection channels 30 to 50. The oscillation frequency of the VCO 4 changes according to the control voltage which is the output voltage of the D / A converter 6.

FIG. 2 shows an oscillation frequency characteristic of the VCO 4 with respect to a control voltage which is an output voltage of the D / A converter 6.

The filter 5 to which the control voltage which is the output voltage of the D / A converter 6 is supplied is for removing a ripple and noise of the output voltage of the D / A converter 6. D / A
The level controller 7 converts a control voltage corresponding to the frequency of the local oscillation signal Lo ₁ of each channel into a parallel input code according to the oscillation characteristics of the VCO 4 and stores the code, and stores a tuning control signal (selection) input at the time of tuning. (Corresponds to station information signal)
It operates so as to read in accordance with the level of.

The local oscillation signal Lo ₂ is supplied from a fixed frequency oscillator 9. The local oscillation signal Lo ₂ is supplied to the mixer ₂ and frequency-converts the intermediate frequency signal IF ₁ into an intermediate frequency signal IF ₂ .

FIG. 3 shows the configuration of the second embodiment.
In the second embodiment, mixers 1, 2, FM detector 3, VCO
4. In addition to the first embodiment of the configuration of the filter 5, the D / A converter 6, the D / A level controller 7, and the fixed frequency oscillator 9, a single loop AFC (automatic frequency control) is performed. I have. In the second embodiment, 8 is an arithmetic unit, 1
8 is an AFC circuit.

Next, the operation of the configuration of the second embodiment will be described. In the second embodiment, together with the operation of the first embodiment, further previously set a reference level to the output voltage with respect to the center frequency of the intermediate frequency signal IF ₂ based on the FM detection characteristic, the reference level and the FM detection output An AFC signal is generated by the AFC circuit 18 based on the difference between the values. This AFC signal by changing the parallel input code of the D / A converter 6 the oscillation frequency of the VCO4 changes, operates to automatically adjust the frequency of the intermediate frequency signal IF _2.

FIG. 4 shows the configuration of the third embodiment. In the third embodiment, mixers 1 and 2, FM detector 3,
VCO 4, in addition to the first embodiment of the configuration of the filter 5, D / A converter 6, D / A level controller 7 and a fixed frequency oscillator 9, the frequency of the intermediate frequency signal IF ₂ automatically adjusts In the second embodiment, 10 is a reference frequency oscillator, 11 is a reference frequency divider, and 12 is a VCO. Reference numeral 13 denotes a fixed frequency divider, 14 denotes a comparison frequency divider, 15 denotes a phase comparator, and 16 denotes a loop filter.

Next, the operation of the configuration of the third embodiment will be described. In the third embodiment, together with the operation of the first embodiment, the reference frequency oscillator 10 is further frequency-divided by the reference frequency divider 11 to generate a phase comparison reference frequency, and the output frequency of the VCO 12 is fixedly divided. After the frequency division by the frequency divider 13, the phase comparison frequency divided by the comparison frequency divider 14 is compared with the phase comparison reference frequency by the phase comparator 15, and the value of the difference is compared with the control voltage of the VCO 12 through the loop filter 16. The local oscillation signal Lo ₂ is generated by the PLL. The previously set the reference level to the output voltage with respect to the center frequency of the intermediate frequency signal IF ₂ based on the FM detection characteristic, and outputs the AFC signal the difference between the reference level and the FM detection output value from the AFC circuit 18. This A
By changing the frequency division ratio of a comparison frequency divider 17 in FC signal, it operates to alter the oscillation frequency of the VCO4 automatically adjusting the frequency of the intermediate frequency signal IF ₂ in.

[0032]

As is apparent from the above description, the tuning apparatus for a double conversion receiver according to the present invention uses the control voltage of the VCO for the local oscillation signal in the first local oscillation section based on the oscillation frequency characteristics of the VCO. Read, stored as a parallel input code of the D / A converter, and based on the channel selection information signal, read out the corresponding parallel input code and
Since the oscillating frequency of the VCO changes according to the parallel input of the / A converter and the output voltage of the D / A converter, there is an effect that a wideband VCO constituting a local oscillation circuit can be easily realized.

Further, since the AFC loop for stabilizing the center frequency of the second intermediate frequency signal is fed back to the control system of the output code of the D / A converter, the setting of the local oscillation signal is realized by a single loop. This has the effect of reducing the signal processing scale. In addition, since the PLL circuit is not used, even if the characteristics of the VCO of the local oscillation unit are non-linear, it is not necessary to consider the loop gain, and the configuration is simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of a tuning apparatus for a double conversion receiver according to the present invention.

FIG. 2 is a characteristic diagram showing an oscillation frequency characteristic of a VCO with respect to a control voltage from a D / A converter shown in FIG.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the tuning apparatus for a double conversion receiver according to the present invention.

FIG. 4 is a block diagram showing the configuration of a third embodiment of the tuning apparatus for a double conversion receiver according to the present invention.

FIG. 5 is a block diagram showing a configuration of a channel selection device for a single conversion receiver used in a conventional BS broadcast receiver.

6 is an explanatory diagram for explaining AFC in the configuration shown in FIG. 5;

FIG. 7 is a block diagram showing a configuration of a conventional tuning device for a double conversion receiver.

FIG. 8 is an explanatory diagram showing a relationship between a frequency band and a local oscillation signal of each channel selection in the configuration shown in FIG. 7;

FIG. 9 is a control voltage-oscillation frequency characteristic diagram used for explaining the non-linear VCO shown in FIG. 7;

[Explanation of symbols]

1,2 mixer 3 FM detector 4 VCO 5 filter 6 D / A converter 7 D / A level controller 9 fixed frequency oscillator Lo _1, Lo ₂ local oscillation signal IF _1, IF ₂ intermediate frequency signal

Claims (1)

(57) [Claims] A first local oscillator for transmitting a first local oscillation signal for converting a high-frequency signal into a first intermediate frequency signal; and a second intermediate frequency signal for converting the first intermediate frequency signal into a second intermediate frequency signal. A second local oscillator for transmitting a second local oscillation signal for converting the signal into an FM signal, and an FM for obtaining an FM detection signal from the second intermediate frequency signal
A first voltage-controlled oscillator, a D / A converter that generates a DC voltage serving as a control voltage of the first voltage-controlled oscillator, and a DC / DC converter. a filter for transmitting said control voltage obtained by smoothing, and a D / a level control to select the DC voltage have based Dzu <br/> the tuning information signal, the second local oscillation unit A reference oscillator, a reference divider for dividing an output signal of the reference oscillator to generate a phase comparison reference frequency signal, a second voltage-controlled oscillator,
A fixed frequency divider for dividing the output signal from the voltage-controlled oscillator, and the output signal from the fixed frequency divider as a channel selection information signal.
A phase comparison frequency divider for delivering a phase-frequency signals variable frequency division in Zui the conversion a phase comparator for detecting a phase error between the phase comparator reference frequency signal and the phase comparison frequency, the phase error into a DC voltage A loop filter for transmitting a control voltage for the second voltage controlled oscillator, a frequency division ratio generator for setting a frequency division ratio of the comparison frequency divider based on a channel selection information signal , A frequency error of the second intermediate frequency signal is detected based on a difference between a reference level and an output signal value from the FM detection circuit.
An AFC circuit that generates an FC signal; and an arithmetic unit that adds or subtracts the AFC signal to or from the output signal of the frequency division ratio generator and inputs the result to a comparison frequency divider to change the comparison frequency division ratio. Characteristic tuning device for double conversion receiver.