JPS5890831A - Tuner - Google Patents

Abstract

PURPOSE:To prevent beat failure, by taking the frequency dividing ratio of a prescaler to a specific value. CONSTITUTION:The range of harmonics where beat failure can normally be suppressed is that the harmonics are apart from a reception frequency by + or -300kHz or more. This is because the characteristics of a filter used for a radio receiver have a band of about 300kHz. Thus, no beat failure takes place when the relation of Equations (1), (2) is satisfied in case of FM broadcast in Japen, where the 1/p is the frequency dividing ratio of a prescaler, (k) is the number of order of harmonics, fs is the reception frequency, fi(=10.7MHz) is the intermediate frequency, alpha is the difference between the reception frequency fs and the harmonics (=300kHz). Thus, in seeking the frequency dividing ratio satisfying the relation, p=16.17 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a grease tuner used in a digital tuner for FM radio.

In recent years, tuners for radio receivers have become increasingly digital, and digital tuners using %KPLL (phase-locked loop) circuits are being developed.

The PLL circuit for digitization is a large-scale integrated circuit (L
However, from the viewpoint of low power consumption, an LSI with a complementary MO8 (hereinafter abbreviated as 0MO8) structure is often used. However, the maximum operating frequency of the 0MO8 structure LSI is 1QMHzQ degrees at a power supply voltage of 5 volts. On the other hand, the frequency of FM broadcasting is approximately 76-110MHz.
Since there is a Q degree, the corresponding local oscillation frequency is directly C'
It is not possible to input to a part of the counter of the PLL circuit of MO8-LSI. Therefore, in the past, E
The radio's local oscillation frequency is set to 0 using a CL (Turnacle Coupled Logic) II frequency divider.
MO8-I'! After dividing the frequency to the operable frequency of I, the PL
It is input to a part of the counter of the L circuit.

Gliskeller mainly uses a known pulse swallow type, usually (1/10, h711).

(1/20, 1/21) I (1/20, 1/
22') l (1/40.1/44) combination of frequency division has been mainly used. Because 0MO8
Since the maximum operating frequency of the PLLL8I counter part of the structure is about 10 MHz at a power supply voltage of 5 volts, the maximum local oscillation frequency of FM broadcasting is about 120 MHz, so the frequency division ratio of the grease cracker is l/10. This is because the above division values are required. However, if a digital circuit is constructed using a Grisscaler with the above division ratio, the signal line between the output end of the Grisker 2 and the input end of the PLL circuit is There was a drawback that harmonics jumped out from the FM broadcasting station and caused beat interference with the receiving frequency at certain FM broadcasting stations.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cheese having a greasing scale having a frequency division ratio that does not cause beat disturbances.

The present invention improves the division ratio of Grisketto to 1/16 or 1/1.
The present invention will be explained in more detail below.

Usually, the range of harmonics in which beat disturbance can be suppressed is when the harmonics are away from the receiving frequency by ±300 kHz or more. This is because the filter used in the radio receiver has a characteristic of 300kHz! This is because it has a passband width of 1.

IE-1), the Briskeller's splitting ratio is now 1/p, the harmonic order is set to f3. intermediate frequency t fH
(=10.7MHz), and the difference between the received wave number f and the high frequency is α (=300kHz), then Japan OFMFM
In broadcasting, beat failure will not occur if the following relationship is satisfied.

(f, -11)X-) f, ten α...
...(1) (f, -f 1 ) x-(f, -α
・'・”'(2) The above equations (1) + (2) are equations that respectively define the upper limit (+300 kHz) and lower limit (-300 kHz) of the frequency at which harmonic components are eliminated by the filter.

becomes.

The allowable range of input frequency is 9QMHz≧f.

If ≧76MHz, the harmonics are ' smax (=9
0MHz)+6 or more, it is within a range that satisfies equation (3). On the other hand, the Tame frequency is flml.

(=76MHz) In order to be 7a or less, it is within the range of - that satisfies equation (4).

For FM broadcasts in Western countries, the range of (-) that does not cause beats is determined as follows.

From formula (1)' s (2)', here % 'amin -8IsMHz * f@1n
A-107,9MHz g f 1 = 1α7MHg
*A=300kHz.

From the relationship of the above equations (5) * (6) and (5)' I (6)', the frequency division ratio and harmonic order p that cause beat disturbance are
When the combination of , and is represented on a graph, it is as shown in FIG. Therefore, as is clear from Figure 1, the 1 frequency division ratio is (1
/16°1717), it can be seen that there are no harmonics that cause beats.

In this way, the frequency division ratio according to the present invention (1/16.1/17
) can provide a digital channel with good reception sensitivity that is not affected by harmonics from the output line of the grid.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the frequency division value p that causes a beat disturbance and the harmonic order.

Claims (1)

[Claims] The device is characterized by using a grease cracker with a frequency division ratio of 1/164 or 1/17.