JPS59218049A - Channel selecting device - Google Patents

Abstract

PURPOSE:To attain easily an economical fine adjustment by using a PLL circuit of a pulse swallow system and obtaining fine adjustment data for adjusting finely a tuning frequency. CONSTITUTION:A programmable frequency divider 2 of the PLL consists of a swallow counter 9 and a programmable counter 8. Further, a 2-modulus prescaler 11 whose output is given to the programmable frequency divider 2 and to which an output of the counter 9 is fed back is provided and a control section 12 is connected to the frequency divider 2. The control section 12 forms data adjusting finely the receiving frequency. An automatic fine adjusting signal is supplied to a comparator 13 and its output is fed to a controller 14 together with a manual fine adjusting signal. The controller 14 generates the fine adjusting data signal and its signal is stored in an RAM15. An output of the controller 14 is stored temporarily in a register 16. The content of the register 16 is decentralized and connected to two counters in the PLL loop.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a channel selection device used, for example, in a television receiver, and particularly to fine adjustment of a receiving frequency.

In recent years, phase-locked loops (hereinafter referred to as 1-PLL J) have been used in television channel selection devices, etc.
kedLoop). ) One type of synthesizer is used.

In this PLL, a fixed frequency division system configuration as shown in FIG. 1 is used in order to widen the operating range. That is, in the PLL, the voltage controlled oscillator 1 (hereinafter 1'-
It's called VCOJ. ) has a high oscillation frequency fi, TTL
If the operating range of the programmable divider 2 consisting of +MO8 is exceeded, the PPL will not operate correctly.

For this reason, a Grisscale 23 is placed before the programmable divider 2, and fixed frequency division is performed to lower the input frequency to the programmable divider 2.

In Fig. 1, 4 is a 7-alesis frequency generator, 5 is a phase comparison circuit, the comparison value is input to a charge pump 6, and the output of this charge pump flow is input to the VCOI via a low-pass filter 7. has been done.

Here, the oscillation frequency of the VCOI=if. SC%'J The reference frequency of the reference frequency generator 4 is 'rl, the prescaler 30, the frequency division ratio is P1, and the frequency division ratio of the programmable divider 2 is N, then fosc=P-N-f. Therefore, by changing the frequency division ratio N, the local oscillation frequency of the broadcast station to be received can be obtained from the VCOI.

Incidentally, although the transmission frequency from a broadcast station is determined in advance, in reality, the transmission frequency often does not exactly match the determined frequency. Therefore, fine adjustment is made on the TV set side to set the VCO oscillation frequency f to the optimum training point. S
Adjusting C. To this end, the frequency division ratio of the frequency divider 20 is changed minutely, perhaps one at a time. Now, f when the frequency division ratio N of programmable divider 2 is shifted by 1. The difference Δfosc of SC is Δfosc ” P ・(N+1) −f, −P−N−
f.

It becomes P-fr. Therefore, the oscillation frequency f when changing the division ratio of programmable divider 2 by N'&'1
. SC changes by a value obtained by multiplying the reference frequency f by P, which corresponds to the frequency division ratio of the grease scaler. This ΔfoBc becomes one step of the fine adjustment. That is, it has the disadvantage that the steps are rough and fine tuning to the optimum tuning point of the receiving frequency cannot be performed. For example, when this method is used for television, if the division ratio of the prescaler 3 is 256 and the reference frequency is increased by l, the l step that can be finely adjusted becomes 256IΦ2, which is too large in reality. .

A method is also known in which the frequency division ratio of the reference frequency generator is made programmable for fine adjustment.

However, this method has the disadvantage that the frequency resolution differs depending on the receiving frequency and that the reflex frequency generator is expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a channel selection device that has a small variable frequency in l steps, is stable in operation, and can easily perform economical fine F1.1 adjustment.

The present invention focuses on employing a pulse/swallow type in the PLL circuit to enable fine adjustment. That is, the present invention uses a pulse/swallow type PLL circuit to obtain fine adjustment data for finely adjusting the tuning frequency, and based on this data, swallow counter data used in the pulse/swallow type is adjusted. The feature is that the frequency division ratio is changed by changing the frequency division ratio first.

An embodiment of the present invention will be described based on the drawings. Figure 2 shows
FIG. 1 is a configuration diagram of an embodiment of the present invention. Compared to the conventional configuration explained in FIG. - includes a 2-modulus scaler 11 to which the output of the counter 9 is fed back;
There is a D. The frequency division ratio for the frequency divider 2 is set separately for the swallow counter 9 and the programmable counter 8, and the lower data of the frequency division ratio is set for the swallow counter 9. The prescaler 11 has two frequency division ratios, and divides the signal from the VCO1 by one of the frequency division ratios depending on the output of the swallow counter 9.

The control unit 12 creates data for finely adjusting the reception frequency. This fine adjustment data is obtained from an automatic fine adjustment signal created by the tuning device itself using the detection output, etc., and a manual fine adjustment signal created by a person operating from outside the set. The automatic fine adjustment signal is supplied to a comparator 13.

The output of this comparator 13 is supplied to a control device 14 together with a manual fine adjustment signal. The control unit w14 generates a fine adjustment data signal which is stored in a RAM (Random Access Memory) 15 as the fine adjustment step width and direction. The output of the controller 14 is temporarily stored in a register 16. The control device ffi+4, together with the above-mentioned fine adjustment data,
In order to receive a predetermined broadcast station, a frequency division ratio corresponding to the broadcast station is also generated. Therefore, the contents of register 16 are:
The coupling circuit IO distributes and connects the two counters included in the PLL loop. That is, the lower data of register 16 is sent to swallow counter 9, and the lower data of register 16 is sent to swallow counter 9.
The upper data of 6 is coupled to a programmable counter 8, respectively. When this control section 12 is used only for fine adjustment control, the coupling circuit 10 includes only a circuit that supplies the lower digits of the register 16 to the swallow counter 9, and omit the circuit that supplies the upper digits to the programmable counter 8. You can stay there.

The rest of the configuration is the same as the conventional configuration explained in FIG. 1, so the explanation will not be repeated.

In such a configuration, the two frequency division ratios of the 2-modulus Griskey 211 are P and P+1. If the preset value of the swallow counter 9 is "Is" and the preset value of the programmable counter 8 is Np, then the oscillation frequency f of the VCOI is
. sc is fosc ” t (Np-n, ) ・P+nt (
P+1)')'r.

However, the frequency division ratio N of programmable divider 2 is N = PNp 10.

becomes. Here, "1" indicates the lower data of the frequency division ratio, and Np indicates its upper data. Therefore, the swallow
When the counter 9 counts one and changes by Nil, the change ΔfO8c in fQf3C is Δ'osc"((
NP-(n++1))P+(nt+1)(P+1))
fr-((NP-nt) P+nt (P+ 1)
) fr= (-P+(P+1)) f.

=f.

and matches the value of the reference frequency. In other words,
Compared to the PLL having the conventional configuration shown in FIG. 1, detailed fine adjustment is possible regardless of the grease scaler 3 (FIG. 1).

Next, the operation will be described. Frequency division ratio data corresponding to a broadcast station desired to be received is set from the control device 14 to the swallow counter 9 and programmable counter 8 of the frequency divider 2 via the register 16f. As a result, the oscillation frequency of the VCOI is 17f. 8c is controlled by a PLL circuit so as to obtain a local oscillation frequency corresponding to the broadcast station to be received, and as a result, becomes in a receiving state. However, if it is detected that the receiving frequency and the tuning frequency are out of alignment, the deviation is provided to the comparator 13 as an automatic fine adjustment signal. This automatic fine adjustment signal is compared with a reference voltage by a comparator 13, and this comparison value is input to a control circuit 14. The control device 14 determines the direction of fine adjustment (increase or decrease osc) according to the processing of the built-in zologram, and inputs one by one from the swallow counter 9 indicating the lower data of the frequency division ratio N via the register J6. The frequency division ratio N is changed one by one by counting positively or squarely. Accordingly, f of VCOl. SC changes with reference frequency fr in one step. When synchronization is achieved, this fine adjustment control 1
141 operation ends. If the tuning goes out again, the above operation is performed again, and correct tuning is always achieved. In the case of manual fine adjustment, a manual fine adjustment signal is input to the control device 14 to perform similar control.

During these fine adjustment controls, it is preferable to maintain the degree of fine adjustment by storing the number and direction of fine adjustment steps in the RAM 15. For example, I? , AM15 is taken as one step, and the stored contents are incremented or decremented by one each time the @ key control is performed. It is also preferable to use another bit in RAM 15 to determine the direction of fine adjustment.

As explained above, according to the present invention, the conventional PLL is provided with an additional circuit that can make the change in the oscillation frequency of the VCO due to the change in the frequency division ratio match the reference frequency,
Further, since a control section is provided that increases or decreases the frequency division ratio one by one in accordance with the shift in the tuning frequency, fine tuning of the reception frequency can be performed. This circuit is stable due to the characteristics of a PLL circuit, and has a simple circuit configuration, making it economical. Further, since the amount of change does not differ for each frequency, the @adjustment step becomes uniform depending on the selected frequency. Therefore, according to the present invention, it is possible to provide a channel selection device that can perform stable fine adjustment.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example, and FIG. 2 is a block diagram showing an embodiment of the present invention. 1...Voltage controlled oscillator, 2...Programmable divider, 3...Grise scaler, 4
・・・・・・7 Allens frequency generator, death...
Phase comparison circuit, 6...Charge pump, 7...
...Low pass filter, 8.Old...Swallow counter,
9...Programmable counter, 10...
...Coupling circuit, 11...-2 modulus prescaler, 12...Control unit, 13...Comparator% 14...Control device, 15...・
・・几AM、16・・・・・・Register. ! Kotobuki 1 diagram Kaz diagram

Claims (1)

[Claims] A grease scaler that divides the output signal of the voltage controlled oscillator by a first frequency division ratio or a second frequency division ratio and outputs the result, and a programmable divider that divides the output signal of the grease scaler by a set frequency division ratio and outputs the result. a frequency divider, the programmable frequency divider is configured with a swallow counter and a programmable counter, and a frequency division ratio to be set in the programmable frequency divider is set separately for the swallow counter and the programmable counter. , by comprising a pulse swallow one-type phase-locked loop circuit that controls the frequency division ratio of the grease scaler to be the first frequency division ratio or the second frequency division ratio based on the output of the swallow counter. , in a tuning device for receiving a broadcasting station corresponding to a frequency division ratio set in the programmable frequency divider, means for obtaining fine adjustment data for finely adjusting a tuning frequency; All features include means for changing the frequency division ratio set in the programmable frequency divider by first changing the frequency division ratio data set in the swallow counter. Channel selection device.