JPS6387010A - Digital tuning circuit - Google Patents

Abstract

PURPOSE:To obtain a digital tuning circuit which can work at the low level of voltage by using a circuit that performs switch between the signal obtained by dividing the output of an FM receiving IF amplifier and the output of said IF amplifier and integrating these output and signal to count the outputs of integration. CONSTITUTION:An IF signal of 10.7MHz intermediate frequency is amplified 11 to undergo the FM wave detection 12 as well as the level detection 13. The IF signal is divided 14 and supplied to an FM/AM switching circuit 15. An IF signal of 455KHz for AM reception is amplified 17 to undergo the AM wave detection 18 and also supplied to the circuit 15. The output of an AM wave detecting circuit 18 is supplied to a display device driving circuit 16 after AGC 19. At the same time, the detected 13 FM level is also supplied to the circuit 16. The output of the circuit 16 is muted 20 together with the output of the circuit 15. These said circuits are turned into integrated circuits and these outputs are supplied to a digital tuner 21 through an output terminal. Thus it is possible to obtain a digital tuning circuit of C-MOS which can work at a low level of voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement of a digital tuning circuit that performs tuning by counting the output of an IP amplifier.

(Prior Art) Conventionally, a digital tuning circuit that performs tuning by counting IF (intermediate frequency) is configured as shown in FIGS. 3 and 4.

First, in Fig. 3, when receiving AM, A in the integrated circuit IC is
The IF low signal buffer amplifier 2 output from the IF amplifier 1 for Tuner circuit 3 is AM
Auto-tuning is performed by counting seven to the intermediate frequency of 455. Similarly, when receiving FM, the signal is input to the IF low signal buffer 5 output from the FM IF amplifier 4 in the integrated circuit IC, and the output of the buffer 5 is led to the output terminal 0UT2.

When inputted from the output terminal 0UT2 to the FM input of the digital tuner circuit 3 which includes a count of C-MO3i, the digital tuner circuit 3 receives the FM intermediate frequency 10.
After counting 7MH7, the count is stopped and auto-tuning can be performed.

In addition, in FIG. 4, an FM configured in the integrated circuit IC
After the output of the IP amplifier 6 is detected by the FM detection circuit 7, the S curve of the detection output is
It is detected by the curve detection circuit 8. LE that lights up the LED when the detected deviation level is within the set value and when synchronized
The output levels of the D drivers 9 are each input to an AND circuit 10, and when there is an output from the AND circuit 10, a stop signal is output to the digital tuner circuit for auto-tuning.

- (Problem to be Solved by the Invention) The digital tuning circuit shown in FIG. C-MO3″?
-The configured counter not only had a slow counting speed, but also became unreadable when the power supply voltage was low, making it unsuitable for low voltages. Also, the IFF signal output is AM and FM.
Since the signals are derived from the output terminals of separate integrated circuits for reception, the connection with external circuits becomes complicated as the number of integrated circuits increases.

Further, in the device shown in FIG. 4, if there is a shift in the center frequency of the S curve when tuned to the receiving station, malfunction will occur. Furthermore, since it is not compatible with AM reception, it is not only necessary to use an expensive narrow band ceramic filter, but also the operation is unstable.

Therefore, the present invention eliminates the above-mentioned problems, and A M /'F
To provide a frequency counting type digital tuner circuit which is compatible with M, has only one IF multiplied signal output terminal of an integrated circuit, and is capable of stable operation at low voltage.

(Structure of the Invention (Means for Solving Problems)) The digital tuner circuit of the present invention is connected to the output side of an IF amplifier for FM reception, and is a frequency dividing circuit that divides the frequency of the output signal of this IF amplifier. A circuit and a switching circuit which receives the output signal of the frequency dividing circuit and the output signal of an IF amplifier for AM reception as inputs and switches and outputs these output signals according to the respective modes are integrated into an integrated circuit, and the switching circuit It consists of an output terminal for deriving the output of the circuit as the output of the integrated circuit, and a digital tuning means composed of a C-MO3lli that inputs the output signal of this output terminal and counts a predetermined number.

(Function) The present invention divides the frequency of the FM IP signal using a frequency dividing circuit to lower the frequency of the C-MO.
It becomes possible to count frequencies using a digital tuning means integrated with S.

Further, the output pin for the AM/FM IF signal of the integrated circuit, which manually switches and outputs the AM and FM IFF signal outputs within the integrated circuit, can be shared.

(Example) An example of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, the FM IP amplifier 11 input to the IF multiplied signal input of the intermediate frequency 10.7M)tz is 10,
After amplifying the 7MHz IF signal, the FM detection circuit 12
The signal is input to the detection circuit 13 at a level for detecting the FM level. Further, the signal is inputted to the IF multiplied signal frequency dividing circuit 14, where the frequency is divided, and then outputted to the FM/AM switching circuit 15. The output of the level detection circuit 13 is input to a display drive circuit 16, which drives the display according to the output level of the level detection circuit 13.

The AM IF amplifier 17 input to the IF multiplied signal input of the intermediate frequency 455K) tz amplifies the IF multiplied signal and inputs it to the AM detection circuit 18.
Enter 5. After detection in the AM detection circuit 18,
6 input to the display drive circuit 16 via the GC circuit 19
The output of the display drive circuit 16 is input to the muting circuit 20, and the output of the FM/AM switching circuit 15 is also input to the muting circuit 20. The output of the muting circuit 20 is led to the output terminal OUT of the integrated circuit IC.

The above muting circuit 20 is housed in an integrated circuit IC. An FM or AM IF signal is switched to the output terminal OUT by the FM/AM switching circuit 15 and outputted as desired. The output of the output terminal OUT is C-MO
The signal is input to a digital tuner circuit 21 formed of an integrated circuit of S. The digital tuner circuit 21 has a circuit configuration in which the input FM or AM IF multiplied signal is counted and when a predetermined number of signals are counted, auto-tuning is performed.

Even if the digital tuner circuit 21 is a C-MO3II digital counter or an FM multiplied signal is input, the frequency is divided to a lower frequency by the frequency divider circuit 14, so that low voltage driving is possible. Therefore, although the C-MOS counter is slow in counting, the frequency is not lowered, so the IF multiplied signal of FM can be used without any problem. In addition, the FM/AM switching circuit 15 uses an FM or AM IF multiplied signal t&multiply of 1%.
Since it is derived from one terminal of Ic, the number of pins of the integrated circuit IC can be reduced and the connection with the digital tuner circuit 21 can be simplified.

FIG. 2 specifically shows the main parts of FIG. 1.

It is amplified by an IF amplifier 11 formed by an IF multiplied signal differential amplifier A1 for FM, and its output is sent to an FM detection circuit 1.
2 and the frequency divider circuit 14, the frequency divider circuit 14 is composed of flip-flops FFI to FF3, and the input I
The P-times signal is frequency-divided to 1/8 and output, and the frequency-divided output is outputted via the differential amplifier A2 and AI to the output terminal OUT, from which it is output to the digital tuner circuit 21.

Digital tuner circuit 21 is 10.5MHz
After counting 1/8 frequency, auto-tune.

The differential amplifier A2 operates when the FM/AM changeover switch SW, which is turned on only during FM, is turned on. Further, the differential amplifier A3 is turned on only when the display is lit by using the display lighting current I.

It is amplified by an IF amplifier 17 composed of an IF multiplied signal differential amplifier A4 for AM, and its output is sent to the AM detection circuit 1.
8 and 0% to supply differential amplifier A5, differential amplifier A5
operates when the FM/AM changeover switch SW is turned off, and outputs the IF multiplied signal to the output terminal OUT. Output terminal OU
Input from T to digital tuner circuit 21, 455K)
If fz count, auto tune.

Here, the differential amplifiers A2 and A5 are the FM/AM switching circuit 15.
, and the FM/AM changeover switch SW is FM/
This is a mode switching switch for switching the AM switching circuit 15 and outputting an FM divided signal or an IF multiplied signal of AM to the output terminal OUT.

[Effects of the Invention] As described above, according to the digital tuning circuit of the present invention, it is possible to use a C-MOS digital tuner circuit that can operate at low voltage by dividing the frequency of an IP multiplied signal for FM. Not only is this possible, but it can also be derived from a common output pin of the FM and AM IF multiplication signal integrated circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram embodying the main parts of FIG. 1, and FIGS.
Each figure is a conventional Ri diagram. 11... IF amplifier for FM 14...
...Frequency divider circuit 17...AM IF amplifier 15...
...FM/AM switching circuit IC...
・Integrated circuit 0tJT・・・Output terminal 21・・・Digital tuner circuit applicant
Toshiba Corporation Toshiba Audio/Video Engineering Corporation

Claims (1)

[Claims] A frequency dividing circuit connected to the output side of the IF amplifier for FM reception and dividing the frequency of the output signal of this IF amplifier, and inputting the output signal of this frequency dividing circuit and the output signal of the IF amplifier for AM reception, At least a switching circuit that switches and outputs these output signals according to each mode is integrated into an integrated circuit, an output terminal that derives the output of the switching circuit as the output of the integrated circuit, and an output signal of this output terminal that is input. 1. A digital tuning device comprising a C-MOS-configured digital tuning means for counting a predetermined number of times.