JPS60247321A - Tuning detector of radio receiver - Google Patents

Abstract

PURPOSE:To secure the extremely exact synchronism between a radio receiver and a center frequency by using a PLL consisting of a voltage control crystal oscillator which oscillates with an intermediate frequency and detecting a tuning point from an AND obtained between the output of a reception level detector and the output obtained when the PLL is locked. CONSTITUTION:A certain frequency is received in a sweep mode by a receiver and put into the characteristics of an intermediate frequency band filter 6. In such a case, a level detector 25 is actuated. Then a VCXO22 is locked when a local oscillator 4 is swept and synchronized with a frequency fo, and a search stop signal is delivered to a terminal 27 owing to an AND obtained between the output of the detector 24 and the output of the detector 25. If the fo is set at 10.7MHz, the VCXO22 is locked only when the intermediate frequency is set within fo+ or -1kHz. Thus it is possible to deliver the search stop signal at an exact tuning point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a sweep receiver, and particularly to a sweep receiver that can accurately detect the tuning point of a received signal.

[Conventional technology]

Conventional circuits of this type include those shown in FIGS. 3 and 4.

3 is mainly used for FM tuners, and FIG. 4 is mainly used for AM tuners (including LW and SW).

In Fig. 3, 1 is an antenna, 2 is a high frequency amplification circuit,
3 is a mixer, 4 is a local oscillator, 5 is a PLL synthesizer, 6 is an intermediate frequency band filter, 7 is an intermediate frequency amplifier, 8 is an FM demodulator, 9 is an FM demodulation output terminal, 10 is a low-pass filter, 11 is a window comparator, 12 is a tuning detection output terminal.

Further, in FIG. 4, numerals 1 to 7 have the same functions as shown in FIG. 3, 13 is an AM demodulator, 14 is an AM demodulation output terminal,
15 is a narrowband filter for intermediate frequency carrier wave detection, 16 is an intermediate frequency amplifier, 17 is a level detector, and 18 is a tuning detection output terminal.

In the FM tuner shown in FIG. 3, an intermediate frequency carrier wave provided by an intermediate frequency amplifier 7 is applied to an FM demodulator 8 for FM demodulation, and is also applied to a low pass filter 10, where a DC component is extracted. That is, the output obtained by this low-pass filter 10 is a so-called S-curve output that draws a symmetrical curve with fo as the center, as shown in FIG. This output is applied to a window comparator 11 which has a window voltage at VO in FIG. 5 and therefore acts to provide an output at terminal 12 near fO. That is, this output becomes a tuning point detection output and is used as a search stop signal of the receiver.

In addition, in the AM tuner shown in FIG.
By amplifying the signal and level-detecting it by the Rel detector 17, it is provided to the terminal 18 as a tuning point detection output. FIG. 6 shows this situation. There is a sideband B of the carrier wave for the carrier wave A, and C shown by the broken line represents the pass characteristic of the intermediate frequency band filter 6, and D shown by the dashed line represents the pass characteristic of the intermediate frequency band filter 6. represents the pass characteristic of the narrowband filter 15 for intermediate wave carrier detection. Therefore, when the carrier wave A enters the region indicated by the chain line, a search stop signal is provided to the output terminal 18.

Here, if the frequency interval of the broadcasting stations is set faithfully to the communication system and is equal to or greater than the occupied bandwidth, malfunctions will not occur in the search stop of the sweep receiver even in the conventional examples shown in FIGS. 3 and 4.

However, for example, in the case of FM broadcasting, the modulation frequency is 5
Even though the frequency is up to 3KH* and the occupied bandwidth is over 200KH2, there are stations with 10KHz steps, so the local oscillator PLL synthesizer is also 10KHz.
It is necessary to sweep in KHz steps. For this reason, if the S-curve output deviates as shown by the arrow A or the arrow in Figure 7 due to the temperature or humidity characteristics of the inductance or capacitor that constitutes the demodulator, the search stop signal will change to f.
.

10KHz or several 10KH in front of the sweep direction instead of
This causes the inconvenience that the signal is output before z.

Considering this fO, 25KHz is approximately 20ppm/''c in the range of -20℃ to +80℃, which is outside the range of the temperature or humidity characteristics of the variable inductance or variable capacitor, so it is virtually accurate. It is difficult to make it work.

Also, in the case of AM tuners, especially LW.

In the MW band, there are cases where the station location is IKHz, so the PLL synthesizer of the local oscillator is also
I have no choice but to sweep with KH2 steps.

However, when the carrier wave A is modulated as shown in Fig. 8, when the sideband B of the modulated wave enters the band of the narrow band filter 15 for carrier wave detection, a search stop signal is output and the tuning is not correct. This causes the inconvenience of entering the receiving state in the current state.

[Object of the present invention]

The present invention aims to eliminate the above-mentioned disadvantages of the conventional ones and provide a tuning detector that can accurately detect tuning to the center frequency in a radio receiver that performs step reception using a PLL synthesizer as a local oscillator. That is.

[Example of the present invention]

FIG. 1 shows a first embodiment in which the present invention is applied to an FM tuner, and numerals 1 to 7 are the same as those of the conventional FM tuner shown in FIG.

19.20.21 is a phase comparator, 22 is a voltage controlled oscillator (hereinafter referred to as VCO), 23 is a voltage controlled crystal oscillator (hereinafter referred to as VCXO), 24 is a lock detector, 2
5 is a level detector, and 26 is an AND gate.

Note that 27 is a tuning detection output terminal, 28 is an FM demodulation output terminal, R1 and C1 are a resistor and a capacitor that constitute a low-pass filter, and R2 and C2 are a resistor and a capacitor that similarly constitute a low-pass filter.

In this FIG. 1, the intermediate frequency signal provided by intermediate frequency amplifier 7 is applied to phase comparator 19. In FIG. The output of this phase comparator 19 is connected to the resistor R1 and the capacitor -'J
'C+, and its output is applied to the VCO 22. The output of this VC,022 is applied to the other input terminal of the phase comparator 19, and as a result constitutes PL'L. Therefore, an FM demodulated output is provided at the output terminal 28 by the action of the PLL.

The output of the VCO 22 is applied to the phase comparator 204,
Its output is applied to a low-pass filter consisting of resistor R2 and capacitor C2, and its output is applied to VCXO23, and the output of vCX023 is applied to the other input terminal of the phase comparator 20 to form a PLL. There is.

1) LL including VCXO23 with crystal oscillator as reference source
provides its output to one end of the phase comparator 21,
The phase of the signal is compared with the intermediate wave signal applied to the other end of the phase comparator 21, and the signal is applied to a lock detector 24, which is formed of, for example, a Schmitt trigger circuit.

The output of this lock detection N24 enters one of the AND gates 26-, and the output of level-detected intermediate frequency signals is applied to the other input terminal of this AND gate 26,
D is provided at the output terminal 27 as a tuning detection signal, ie a search stop signal.

Therefore, if a frequency is received in which the receiver is in the sweep state and falls within the characteristics of the intermediate frequency bandpass filter 6, then
Level detector 25 operates. And further local oscillation R
4 is swept and tuned to fo, the VCXO 22 is locked and the output of the lock detector 24 and the level detector 2
The search stop signal is output to terminal 2 by ANDing the output with 5.
7 will be output.

Unlike the above-mentioned VCXO beam, C oscillator, etc., the drift range with respect to temperature and humidity is -20"C to +80"C.
Also, it is less than ippm/'c, and fo is 10.7
In the case of MHz, locking will not occur unless the intermediate frequency falls within fo±IKHz, and as a result, it is possible to output the search stop signal at an accurate tuning point.

In this embodiment, the output of the level detector 25 and the output of the lock detector 24 are applied to the AND gate 26, but this means that if there is no antenna input, there is no capture effect in the case of FM, and the intermediate The frequency amplification stage has a high gain against noise, and the VCXO at the center of the intermediate frequency band noise
This is to avoid locking and outputting an erroneous search stop signal.

FIG. 2 shows a second embodiment in which the present invention is applied to an AM receiver, and the same functional parts as in FIG. 1 are designated by the same reference numerals.

The VCX023 in this embodiment is configured to oscillate at a frequency four times the intermediate frequency, and is applied to the phase comparator 20.21 via the 1/4 frequency divider 30.

In this case, the AM demodulated output is output to the terminal 29 as a phase comparison output between the PLL output locked to the intermediate frequency and the intermediate frequency, that is, a synchronous detection output.

This AM tuner also uses an AND gate 26, but this is because in the case of an AM tuner, when there is no antenna input, the AGC effect decreases and the intermediate frequency amplification stage has a high gain against noise, and the VCXO This is to prevent the search stop signal from being erroneously output due to locking.

[Effects of the present invention]

Since this invention is made as described above, it is possible to tune the receiver to the center frequency very accurately.
Good quality demodulated output can be obtained without distortion.

[Brief explanation of drawings]

Figure 1 is a block diagram of an FM receiver using this invention.
Figure 2 is a block diagram of an AM receiver using this invention.
Figure 3 shows an example of a conventional FM receiver. 4 is a block diagram showing an example of a conventional AM receiver, FIG. 5 is a characteristic diagram showing the S-curve output obtained by an FM detector, and FIG. 6 is a block diagram showing an example of a conventional AM receiver. No. 71D' is a characteristic diagram showing the relationship between the carrier wave and filter characteristics in , No. 71D' is a characteristic diagram of the S curve output when drift occurs, and Fig. 8 is a characteristic diagram showing the search stop situation in a conventional AM receiver. . 3...Mixer, 4...Local oscillator, 5...PL
L synthesizer, 6... intermediate frequency band filter, 7
...Intermediate frequency amplifier, 19-21...Phase comparator,
22... Voltage controlled oscillator (VCO), 23... Voltage controlled crystal oscillator (VCXO), 24... Lock detector, 25... Level detector, 26... AND gate, 27... Tuning detection output terminal, 28...FM demodulation output terminal, 9...AM demodulation deer terminal 30...Bow/
4 frequency divider patent applicant Pioneer Corporation! ”1 side fO Figure 6

Claims (1)

[Claims] A radio receiver that performs step reception using a PLL synthesizer as a local oscillator circuit includes a reception level detector connected to an intermediate frequency amplification stage, and a voltage-controlled crystal oscillator that oscillates at the intermediate frequency carrier frequency of the intermediate frequency amplification stage. A tuning point of a radio receiver is detected by ANDing the output of the reception level detector and the output generated when the PLL is locked to an intermediate frequency carrier frequency. Detector.