JPS63276314A - Synthesizer tuner - Google Patents

Abstract

PURPOSE:To make the quantity of a change in an oscillated frequency of a local oscillator constant by providing a means supplying a control voltage in response to the phase difference between an output of a reference frequency generating means and an output of a variable frequency division means to the local oscillator. CONSTITUTION:With a keyboard 14 is operated, a CPU 16A varies the frequency division ratio P of a programmable divider 10 in response to an operation signal. Then the oscillating frequency fl of the local oscillator 4 changes and the intermediate frequency f2 and the detected output voltage V are changed attended therewith. The CPU 16A fixes once a frequency division ratio P of the programmable divider 10 so as to monitor whether the output of voltage comparators 7h, 7l is of the same sign or the different sign. When the outputs of the voltage comparators 7h, 7l are of the different sign, the fixed frequency division ratio P is released. On the other hand, when the outputs of the comparators 7h, 7l are of the same sign, the voltage setting data fed to a D/A converter 25 is changed and the fixed frequency division ratio is released when the output of the comparator 7h reaches an 'L' level and the output of the comparator 7l reaches an 'H' level.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention is applicable to, for example, a television receiver or an OTV receiver that receives satellite broadcasting or 0ATV (cable television) broadcasting.
Applied to various broadcast receiving devices such as ATV terminal devices,
The present invention relates to a synthesizer tuner having an AFC (automatic frequency control) function.

``Prior Art'' Conventionally, in a synthesizer tuner that has a PLL (phase lost loop) tuning circuit and a microcomputer that controls this PLL tuning circuit, in order to realize the AFC function, the base frequency oscillator of the PLL is One known method uses a variable frequency oscillator.

FIG. 3 is a diagram showing the configuration of this type of synthesizer tuner with an AFC function.

In Fig. 3, ■ is a frequency mixer, which mixes the received signal (frequency f,) amplified by the high-frequency amplifier circuit in the previous stage, and V
The oscillation output (frequency fρ) of the local oscillator 4 constituted by a CO (voltage controlled oscillator) is multiplied by f, and an intermediate frequency signal (frequency @rz=r+−i″Q) is output. This intermediate frequency signal is , only the necessary band is selected by the bandpass filter 2 and input to the next stage FM detector 3,
FM detection is performed. The detected output of the FIVI detector 3 is supplied to a subsequent signal processing circuit 5, smoothed through a low-pass filter 6, and supplied to a voltage comparator 7 as a detected output voltage ■.

These low-pass filter 6 and voltage comparator 7, AF
C reference reference voltage 8L, L reference oscillator 9.1/N fixed frequency divider [1,1/P programmable divider (variable frequency divider) 10, phase comparator 12, and low-pass filter 13, the local oscillator 4 is A P c loop 20 that corrects oscillation frequency fluctuations and keeps the intermediate frequency f constant at all times.
is configured. That is, the detection output of the F'M detector 3 is smoothed by a low-pass filter, etc., and is supplied to the voltage comparator 7 as the detection output voltage . The oscillation frequency "r" of the PLL reference oscillator 9 is controlled so that it is equal to the PLL reference voltage 8.
The output signal of is divided into 1/N by the frequency divider 11,
The signal is supplied to the phase comparator 12.

On the other hand, the programmable divider lO divides the local oscillation frequency fρ into I/P according to the set frequency division ratio P,
A signal with the frequency fp is supplied to the phase comparator 12. The phase comparator 12 compares the phases of the output signal of the programmable divider IO and the output signal of the frequency divider 11, and outputs a signal according to the phase difference. The detection output according to this phase difference is converted into DC by the low-pass filter 13, and this DC voltage is applied as the AF'C voltage to the varicap 4a functioning as part of the tuning capacitance in the local oscillator 4,
The oscillation frequency rρ of the local oscillator 4 is controlled.

In some cases, a tuning voltage corresponding to the APC voltage is applied to a varicap in a tuning circuit (not shown) to control the tuning frequency (receiving frequency f) of the tuning circuit.

Further, reference numeral 14 in the figure is a keyboard operated when selecting a reception channel, and 15 is a CPU (central processing unit) 16 and a ROM (read only memory) 17.
, RAM (random access memory) 18, l10
(input/output circuit) 19. Then, when a receiving channel is selected by the keyboard 14, the CPU 16 reads out the frequency division ratio P necessary to obtain the local oscillation frequency re corresponding to this channel from the ROM lT, and sets the frequency division ratio P. Set programmable divider ① to 0 via l1019. As a result, the local oscillation frequency f& and the tuning frequency of the tuning circuit are set to predetermined values.

Here, a PLL tuning circuit 21 is configured by the frequency divider 11, the programmable divider IO, the phase comparator 12, and the low-pass filter 13. 13-The loop 22 that goes around the local oscillator 4 is a PLL
It functions so that the phase difference between the output signal of the programmable divider 10 and the output signal of the frequency divider 10 (J) is always constant. Therefore, fp=fr/N (1) holds true, and the programmable divider 10 divides the local oscillation frequency fg by 1/P and outputs it, so the frequency fp is fp =f12/P... (2).

From the above equations (1) and (2), the local oscillation frequency @fC is rQ=rr-P/N (3).

Therefore, as can be seen from the above equation (3), the local oscillation frequency fQ changes according to the division ratio P set to the programmable divider IO, and also changes according to the oscillation frequency fr of the PLL reference oscillator 9. do. That is, the local oscillation frequency fQ is determined by the function of the loop 22 described above.
The frequency division ratio P is accurately fixed to a value corresponding to the frequency division ratio P. On the other hand, if an oscillation frequency fluctuation occurs in the local oscillator 4 and the intermediate frequency [,] changes, the above-mentioned function of the APC loop 20 will cause
The oscillation frequency fr of the PLL reference oscillator 9 changes, and the local oscillation frequency fQ changes accordingly.

This change in the local oscillation frequency f& causes a change in the intermediate frequency f2, and this intermediate frequency r2 is
0 passband and changes the output voltage of the FM detector 3 and the detection output voltage supplied to the voltage comparator 7, thereby increasing the oscillation frequency fr of the PLL reference oscillator 9.
changes, and the output voltage of the phase comparator 12 is returned to its original value.

"To the problem that the invention aims to solve" This synthesizer tuner allows for manual fine adjustment by operating the keyboard 14, and this manual fine adjustment can lead to intentionally shifting the tuning.
In V, offset reception is used to reduce interference from adjacent channels, and in satellite broadcasting, offset reception is used to reduce sparkle noise.

That is, by operating the keyboard 14, the CPU 16 is instructed to change the least significant bit of the frequency division ratio P supplied to the programmable divider IO. As a result, the output frequency rp of the programmable divider 10 changes slightly, and the local oscillation frequency fQ and the opening frequency also change slightly.

In this case, the AFC loop 20 must of course be stopped. However, AFC loop 20
If the oscillation frequency fQ is stopped, the oscillation frequency fQ will drift during viewing, resulting in interference and sparkle noise.

Therefore, in the conventional synthesizer tuner described above, offset reception does not stop the AFC loop 20 and is only possible within a narrow range within the uncontrollable range of the AFC loop 20. In order to widen the range, the sensitivity of the AFC loop 20 must be lowered, which poses a problem in that the AFC function deteriorates.

Therefore, conventionally, as shown in FIG. 4, a D/A converter 25 is provided which converts the voltage setting data VD supplied from the microcomputer 15 into an analog signal, and the output voltage of this D/A converter 25 is converted into an AFC signal. It is known to supply a reference voltage to the voltage comparator 7. According to this, even when manual fine adjustment is performed by operating the keyboard 14, the CPU 16 changes the least significant bit of the voltage setting data VD to make it the AFC reference voltage corresponding to the center frequency of the AFC. , the local oscillation frequency fQ corresponding to manual fine adjustment is maintained by the AFC loop 20. Also, there is no need to intentionally lower the sensitivity of the APC loop 20.

However, even in the case shown in FIG. 4, there is a problem that the amount of frequency change due to manual fine adjustment varies depending on the height of the received frequency and is not uniform.

This is because, as is clear from equation (3) above, the amount of change in the local oscillation frequency fQ caused by manual fine adjustment is determined by the division ratio P set in the programmable divider lO. As shown, the division ratio j
Assuming that it is possible to set up to #< I Q 00, when the division ratio P is changed by 1 in manual fine adjustment, a high frequency channel is received and the local oscillation frequency r (l is 10
When the lever is 0 M, the local oscillation frequency fQ is 10
0/1000=0, 1 MHz change. On the other hand, if a low frequency channel is received and the local oscillation frequency rQ is 50MHz, the local oscillation frequency f
& changes by 50/1000=005MHz. However, if you are receiving a channel with a high frequency,
The width of the frequency change due to manual fine adjustment of l stairup will differ greatly depending on the case where a low channel is being received.

This invention was made in view of the above-mentioned circumstances; manual fine adjustment for offset reception will not be invalidated by the A20 function, and there is no need to deliberately lower the sensitivity of AFC. Needless to say, the object of the present invention is to provide an amplifier tuner that can make the amount of change in the oscillation frequency of a local oscillator constant by manual fine adjustment, regardless of the level of the reception frequency.

``Means for Solving the Problems J'' This invention provides an automatic frequency control function for controlling the oscillation frequency of a local oscillator according to the detected voltage obtained by FM detecting and smoothing an intermediate frequency signal. The synthesizer tuner includes a reference frequency generating means for outputting a constant frequency as a reference, a variable frequency dividing means for dividing the oscillation frequency of the local oscillator by a set frequency division ratio and outputting the result, and a frequency dividing means for outputting the oscillation frequency of the local oscillator by a set frequency division ratio, a phase comparison means for supplying a control voltage to the local oscillator according to a phase difference between the output of the generation means and the output of the variable frequency division means; and a control means for controlling the frequency division ratio of the variable frequency division means; an operation means for supplying an operation signal to the control means according to the channel selection and fine tuning operations; a reference voltage generation means for generating a first reference voltage instructed by the control means; a first voltage comparison means for comparing the detected voltage and supplying a first comparison result to the control means; and a second reference obtained by dividing the first reference voltage at a preset ratio. a second voltage comparison means that compares the voltage with the detected voltage and supplies a second comparison result to the control means, and when the operation means is operated for fine tuning, the control means The frequency dividing ratio of the variable frequency dividing means is changed in accordance with the operation signal supplied from the operation means, and the first reference voltage is changed so that the first and second comparison results are in different states. After the point in time, the first reference voltage is held constant, and if the first and second comparison results become the same during the period in which the first reference voltage is held constant, , again, the frequency division ratio of the variable frequency division means is changed so that the first and second comparison results are different from each other.

"Operation" When the operating means is operated for fine tuning, the control means changes the frequency division ratio of the variable frequency dividing means in accordance with the operation signal, and
The first reference voltage is changed so that the first and second comparison results are in different states. Next, if the first and second comparison results are different from each other,
The first reference voltage is held constant, and this first reference voltage is held constant. If the first and second comparison results are in the same state during the period when the reference voltage of The frequency division ratio of the frequency means is changed. Thereby, the A20 function can be activated at the reception frequency set by the fine tuning operation (manual fine adjustment). Further, the phase comparison means is always supplied with a constant frequency from the reference frequency generation means, and is also supplied with the oscillation frequency of the local oscillator divided by the frequency division ratio set by the control means from the variable frequency division means. In other words, since only the frequency division ratio of the variable frequency division means is controlled by the control means, the amount of change in the oscillation frequency of the local oscillator due to manual fine adjustment is constant regardless of the high or low reception frequency. .

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In this figure, parts corresponding to those in FIGS. 3 and 4 are given the same reference numerals, and their explanations will be omitted.

In FIG. 1, the output voltage of the D/A converter 25 for converting voltage setting data VD supplied from the microcomputer 15A into an analog signal is supplied to the voltage comparator 7h as the first AFC reference voltage vh. be done. Also,
This first AFC reference voltage vh is divided at a predetermined ratio by a voltage dividing circuit 28 made up of resistors rl and r, and the resulting voltage is used as a second AFC reference voltage VQ by a voltage comparator 7Q. supplied to Therefore, the second A
The PC reference voltage VC is always lower than the first AFC reference voltage vh by a predetermined voltage.

Then, the voltage comparator 7h compares the detection output voltage V obtained through the low-pass filter 6 and the reference voltage vh,
The comparison result is 1101 of microcomputer 15A.
Supply to 9A. In other words, when the detection output voltage ■ is higher than the reference voltage vh, the “H” level signal is
When the detection output voltage V is lower than the reference voltage vh, “L”
The voltage comparator 7Q also compares the detected output voltage ■ with the reference voltage VQ, and if the detected output voltage V is higher than the reference voltage VQ,
“When detecting a signal at a high level, the detection output voltage ■ is the reference voltage VQ.
If it is lower than 11019A, the “L” level signal is
supply to

On the other hand, 30 is a crystal oscillator, and the oscillation output of this crystal oscillator 30 is divided into l/N by a frequency divider 11.
The signal is supplied to the phase comparator 12. The microcomputer 15A also includes a CPU 16A that executes APC processing, which will be described later, processing during manual fine adjustment, and the like.
6A, a ROM 17A that stores data necessary to specify the frequency division ratio P of the programmable divider 10, a RAM 18A that is used as a work area, and an I1019A that exchanges various data with the outside. It is configured.

Next, the operation of the above-mentioned embodiment will be explained separately into a normal AFC processing operation and a processing operation using manual fine adjustment.

(1) Normal AFC processing operation First, the CPU 16A inputs the specified voltage setting data VD.
It is supplied to the D/A converter 25 via 1019A. As shown in FIG. 2, the voltage comparator '7h has 2M
The first A has a value higher by a predetermined voltage Vd than the detection output voltage Vs when the regular intermediate frequency fs is input to the detector 3.
An FC reference voltage vh is supplied, and a second AFC reference voltage VQ having a value lower than the detected output voltage Vs by a predetermined voltage Vd' is supplied to the voltage comparator 7Q. As a result, when the intermediate frequency input to the 2M detector 3 becomes higher than the prescribed intermediate frequency rs by a predetermined value fd,
The outputs of the voltage comparators 7h and 7Q both become "H" level, and on the other hand, the intermediate frequency r, becomes the specified intermediate frequency f.
When the voltage becomes lower than s by a predetermined value fd', the voltage comparator 7h
, 7Q both become "L" level.

Then, the CPU 16A determines that the output of the voltage comparator 7h is “L”.
” level, the frequency division ratio P of the programmable divider IO is changed so that the output of the voltage comparator 7Q becomes “H” level. As a result, the frequency division ratio P of the programmable divider IO is changed in the same way as the AFC loop, and the intermediate frequency f, is the specified intermediate frequency fs
The tracking frequency range A1 centered at , that is, the frequency (fs
-fd') to (fs+fd).

Here, the tracking frequency range A is the first AFC reference voltage v
h and the second AF'C reference voltage VQ (Vd+
Since it is determined only by Vd') and is completely independent of the division ratio P of the programmable divider lO, it is always constant regardless of the height of the receiving frequency, that is, regardless of the receiving channel.

(2) Processing operation by manual fine adjustment When the keyboard 14 is operated and manual fine adjustment is performed, the CPU 16A executes the processing operation described below in response to the operation signal supplied from the keyboard 14.

That is, the CPU 16A changes the frequency division ratio P of the programmable divider 10 according to the operation signal supplied from the keyboard 14. Then, the oscillation frequency fQ of the local oscillator 4 changes, and along with this, the intermediate frequency r2 and the detected output voltage V change.

Here, the CPU 16A temporarily fixes the frequency division ratio P of the programmable divider 10, and monitors whether the outputs of the voltage comparators 7h and 7Q have the same sign or different signs.

If the outputs of voltage comparators 7h and 7g have different signs, that is, if the output of voltage comparator 7h is "L" level and the output of voltage comparator 7Q is "H" level, manual Assuming that the offset tuning by fine adjustment has been performed as specified, the division ratio P of the programmable divider IO
The fixation is released and the FC processing operation is resumed as described in step 1 above.

On the other hand, if the outputs of voltage comparators 7h and 7Q are both "H" level and both "L" level, voltage comparison "AZ"
The voltage setting data VD to be supplied to the D/A converter 25 is changed so that the output of the voltage comparator 7e is at the "L" level and the output of the voltage comparator 7e is at the "H" level, and the first AFC standard is set. The voltage vh and the second AFC reference voltage v2 are changed. As a result, when the output of the voltage comparator 7h becomes "L" level and the output of the voltage comparator 7Q becomes "H" level, the fixation of the division ratio P of the programmable divider 10 is released,
The AFC processing operation described above is restarted.

If you want to precisely tune to the specified frequency without performing offset reception, operate the keyboard 14 to cancel the manual fine adjustment mode, and the frequency will be divided based on the data stored in the ROM 17A. The ratio P and voltage setting data VI) are set and tuned to a specified frequency.

The above processing operations enable offset tuning by manual fine adjustment while operating the AFC function. Therefore, there is no need to intentionally reduce the sensitivity of AFC, and highly sensitive AFC operation can be obtained.

Further, the oscillator that generates the reference frequency of the AFC may be of a fixed frequency, and a highly accurate crystal oscillator 30 can be used.

"Effects of the Invention" As explained above, according to the present invention, when the operating means/means is operated for fine tuning, the control means changes the frequency division ratio of the variable frequency dividing means according to the operation signal, and , the first and second comparison results are different from each other.
If the first and second comparison results are different from each other, the first reference voltage is held constant; If the first and second comparison results are in the same state during the holding period, the variable frequency dividing means divides the frequency so that the first and second comparison results become different from each other again. Since the ratio is changed, even if the reception frequency is intentionally shifted by manual fine adjustment, the manual fine adjustment will not be invalidated by the AFC function.
The adjustment range of manual fine adjustment can be expanded without lowering the sensitivity of C. In addition, a constant frequency is always supplied to the phase comparison means from the reference frequency generation means, and a constant frequency is always supplied to the phase comparison means by the control means from the variable frequency division means. The oscillation power of the local oscillator divided by the set division ratio is supplied, i.e.
Since only the frequency dividing ratio of the variable frequency dividing means is controlled by the control means, the amount of change in the oscillation frequency of the local oscillator caused by manual fine adjustment can be made constant regardless of the high or low reception frequency. is obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 shows a voltage comparator 7h in the same embodiment. A diagram to explain the operation of 7Q, Figure 3 is a conventional AFC
Figure 4 is a block diagram showing the configuration of a synthesizer tuner with functions. Figure 4 is a block diagram showing the configuration of a synthesizer tuner with AFC functions that changes the conventional AFC reference voltage. Figure 5 shows manual fine adjustment in the synthesizer tuner. FIG. 3 is a diagram for explaining the amount of change in the oscillation frequency of the local oscillator due to the change in the oscillation frequency of the local oscillator. l...Frequency mixer, 3...FM detector, 4...Local oscillator, 6...Low pass filter, 7h...Voltage comparator (first voltage comparison means),
7Q... Voltage comparator (second voltage comparison means), lO
・・・・・・Programmable divider (variable frequency division means)
11 - Frequency divider, 12... Phase comparator (phase comparison means), 13...
・Low pass filter, 14...Keyboard (operation means) +5A...
・Microcomputer (control means) 21...PL
L tuning circuit, 25... D/A converter (KQBE pressure generation means), 28... voltage dividing circuit, rl+r? ...Resistor 30 ...Crystal oscillator.

Claims (1)

[Claims] In a synthesizer tuner having an automatic frequency control function that controls the oscillation frequency of a local oscillator according to a detected voltage obtained by FM detecting and smoothing an intermediate frequency signal, a reference frequency generating means for outputting a frequency; a variable frequency dividing means for dividing the oscillation frequency of the local oscillator by a set frequency division ratio and outputting the result; an output of the reference frequency generating means; a phase comparison means for supplying a control voltage to the local oscillator according to a phase difference with the output of the means; a control means for controlling a frequency division ratio of the variable frequency division means; and an operation according to tuning and fine tuning operations. operating means for supplying a signal to the control means; reference voltage generation means for generating a first reference voltage instructed by the control means; comparing the first reference voltage and the detected voltage; a first voltage comparing means that supplies the comparison result to the control means; and comparing the detected voltage with a second reference voltage obtained by dividing the first reference voltage at a preset ratio; Second
and a second voltage comparison means for supplying a comparison result of the voltage to the control means, and when the operation means is operated for fine tuning, the control means is configured to adjust the voltage according to the operation signal supplied from the operation means. The frequency dividing ratio of the variable frequency dividing means is changed, and the first reference voltage is also changed, and after the time when the first and second comparison results become different from each other, the first reference voltage is kept constant. If the first and second comparison results become the same state during the period in which the first reference voltage is held constant, the first and second reference voltages are
A synthesizer tuner characterized in that the frequency dividing ratio of the variable frequency dividing means is changed so that the comparison results of the above are different from each other.