JPS6019857B2 - Receiving machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention attempts to configure and integrate a local oscillation circuit for AM reception and a local oscillation circuit for FM reception with a frequency synthesizer in an AM/FM receiver. be.

An example of this will be explained below.

In addition, in this example, the reception band strength of AM broadcasting is 1 to 1.
3MH2, a predetermined band of 100k days 2 is selected by coarse tuning, and broadcasting of a target frequency is selected from the selected band by fine tuning. In FIG. 1, 11 to 18 indicate the AM receiving system,
1 1 is an AM antenna, 12 is a preselector. When receiving AM, the preselector 12 selects the reception band from 1 to 3M.
Among Hz, 1-10, 10-20, 20-30MHz
A received signal in one of the bands is selected, and this received signal is fed and combined to a first mixer circuit 14 through a high frequency amplifier 13.

Further, an oscillation signal S, whose frequency changes, for example, between 55.845 and 85.849 MHZ, is taken out from VF0 (variable frequency oscillation circuit) 41 of a local oscillation circuit 40, which will be described later, by dial operation, and this signal S, , the mixer circuit 1 through the AM side contact A of the band changeover switch 1.
41 is supplied as the first local oscillation signal. In this way, in the mixer circuit 14, only the received signal of the desired receiving frequency among the received signals from the preselector 12 is
For example, the frequency is converted into a first intermediate frequency signal having a frequency of 55.848 MHz, and this first intermediate frequency signal is supplied to the second mixer circuit 16 through the first intermediate frequency amplifier 15.

Further, an oscillation signal S2 with a frequency of 56.3 MH2, for example, is taken out from a fixed oscillation circuit 42 using a crystal oscillator,
This signal S2 is supplied to the mixer circuit 16 as a second local oscillation signal.

Therefore, in the mixer circuit 16, the first intermediate frequency signal is frequency-converted into a second intermediate frequency signal having a frequency of 45 HZ, for example. Then, this second intermediate frequency signal is supplied to the detection circuit 18 through the second intermediate frequency amplifier 17 to demodulate the audio signal, and this audio signal is further transmitted to the low frequency amplifier through the AM side contact A of the band changeover switch 3. 2
1 to the speaker 22.

In addition, 31 to 36 indicate an FM reception system, 31 is an FM antenna, 32 is an antenna tuning circuit, and when receiving FM,
The tuning circuit 32 extracts the reception signal of the desired reception frequency from the reception band range of 76 to 9 MHz, and this reception signal is supplied to the mixer circuit 34, and the VF04
The oscillation signal S from the switch 1 is supplied to the mixer circuit 34 as a local oscillation signal through the FM side dovetail point F of the switch 1.

In this case, the frequency of the signal S can be changed from 65.3 to 79.0 by dialing VF041. It is made to change between Tsumugi 4HZ. Therefore, in the mixer circuit 34, only the desired received signal is frequency-converted into an intermediate frequency signal having a frequency of 10.7 MHz, for example.

This intermediate frequency signal is then supplied to the demodulation circuit 36 through the intermediate frequency amplifier 35 to demodulate the audio signal, and this audio signal is supplied to the speaker 22 through the FM side contact F of the switch 3 and further through the amplifier 21. Then, when receiving AM, the first local oscillation signal S is
, is formed. That is, 40A and 40B indicate PLLs, and in PLL 40B, an oscillation signal S3 of a predetermined frequency is formed in a VCO (voltage controlled variable frequency oscillation circuit) 43, and this signal S3 is sent to a frequency converter 4.
At the same time, the oscillation signal S2 of the oscillation circuit 42 is supplied to the converter 44, and a beat signal S4 having a frequency obtained by subtracting the frequency of the signal S3 from the frequency of the signal S2 is taken out from the converter 44. is supplied to the phase comparison circuit 45.

Further, the oscillation signal S6 of VF046 is supplied to the comparison circuit 45, and its comparison output is supplied to VC043 as its control voltage. In this case, the oscillation frequency of VF046 is
It changes in response to the fine tuning within the above-mentioned 100kHz reception band, and by operating the resonance circuit 56 of the VF046 (fine tuning), the frequency of the oscillation signal S6 becomes 2.25.
It is made to vary between 5 and 2.159 MHZ.

Therefore, in the steady state, the frequency of the signal S6 and the frequency of the signal S4 are equal, so the frequency of the signal S4 is changed from 2.255 to 2.159 MHZ by operating the resonance circuit 56.
Varies between. Since the signal S3 has a lower frequency than the signal S2 by the frequency of the signal S4, the resonant circuit 56
As a result of the operation, the frequency of the signal S3 is 54.045 to 54.
．． It will change between 149MHZ. Also, P.L.
In L40A, a resonant circuit 51 of VF041 is constituted by a variable capacitor (variable capacitor) 51C for coarse tuning operation and a coil 51L, and is further connected with, for example, a variable capacitance diode 51D. and,
The oscillation signal S, of VF041 is supplied to the frequency converter 47, and the oscillation signal S3 of VC043 is supplied to the converter 47 through the AM side contact A of the band changeover switch 2, and from the converter 47, the frequency of the signal S, A beat signal S7 having a frequency obtained by subtracting the frequency of the signal S3 is extracted. This signal S7 is then supplied to the phase detection circuit 48, where the phase is compared with a reference signal of frequency 10 HZ, and a phase comparison output whose level changes as shown in FIG. 2, for example, with respect to the frequency f7 of the signal S7. A signal S8 is taken out and is supplied to the variable capacitance diode 51D as its control voltage.

Therefore, with the operation of the resonant circuit 56 of VF046 constant and the frequency of the signal S3 constant, the variable capacitor 51C
When the frequency f of the signal S is manipulated (coarse tuning), the frequency f of the signal S changes stepwise in response to this manipulation, as shown in FIG.

That is, the reference frequency of the detection circuit 48 is 100kHz.
Therefore, the frequency f7 of the signal S7 is locked to an integer multiple of iookH2.
Hz... (i) N: Satisfies a positive integer.

Then, when the variable capacitor 51C is operated to change its capacitance to △C, the frequency of the signal S, correspondingly, becomes
It should change by Δf.

However, when the frequency f changes by Δf, the frequency f7 of the signal S7 also changes by Δf, and this change causes the level of the signal S7 to change by ΔE, as shown in FIG. Therefore, the capacitance of the diode 51D reversely changes by ΔC, the capacitance change ΔC of the variable capacitor 51C is canceled out, and the frequency f remains constant. However, when the operation amount of the variable capacitor 51C is large and its capacitance change △C is large, and the frequency change △f of the signals S, S7 exceeds 10 HZ, it enters the area adjacent to the one cycle in Fig. 2. That is, in equation (i), the integer N “1”
will satisfy the equation (i}, and therefore,
The frequency f, of the signal S, will change by 100kHz.

Therefore, if the variable capacitor 51C is operated while the operation of the resonance circuit 66 is kept constant and the frequency of the signal S3 is kept constant, the frequency of the signal S, and the third
As shown in the figure, it changes in steps of 100kHz. Furthermore, if the resonance circuit 56 is operated while keeping the operation of the variable capacitor 51C constant, the frequency f3 of the signal S3 will change, so the frequency f7 of the signal S7 should change accordingly, but if the frequencies etc. change, The level of signal S8 changes and the capacitance of diode 51D changes, thereby causing signal S. The frequencies of , etc. change, and the frequency becomes constant.

In this case, the variation width of the frequency f3 of the signal S3 is 1
00kHz, even if the level of the signal S6 changes as shown in FIG. 2 due to a change in the frequency of the signal S3, the level change will occur within the region of one cycle in FIG. i) N in the equation does not change.

In the converter 47, f. ;f3+ et al.
...(ii) holds true. Therefore, from equations (i) and (ii), L = f30N x 100kHz, and since N is constant at this time, if the frequency f3 changes with a variation width of 100kHz by operating the resonance circuit 56, then , and accordingly, the frequency f of the signal S, also changes with a variation width of 100 kHz.

Therefore, the frequency f of the signal S changes in 100 kHz steps by operating the variable capacitor 51C, and changes within the 100 kHz steps by operating the resonance circuit 56. Then, such a signal S,
is supplied to the mixer circuit 14 and frequency conversion is performed, so that the reception frequency for AM broadcasting can be changed in 100kHz steps by operating the variable capacitor 51C, and the receiving frequency can be changed in 100kHz steps by operating the resonance circuit 56. This means that you can change the receiving frequency within.

On the other hand, during FM reception, the oscillation signal S2 of the oscillation circuit 42 is coupled to the converter 47 through the FM side contact F of the switch 2. Therefore, in this case, the frequency f, of the signal S, is changed to 100kHz by the operation of the variable capacitor 51C.
Since the signal S changes in two steps and is supplied to the mixer circuit 34, the variable capacitor 5
The reception frequency can be changed in 10 HZ steps by operating 1C.

In this way, according to the present invention, the local oscillation circuit 40 can be made common to the AM receiving system and the FM receiving system, and
The local oscillation circuit 40 can be configured by a frequency synthesizer.

Therefore, the configuration can be simplified, costs can be reduced, and moreover, stable reception can be achieved.

FIG. 4 schematically shows an example of the detection circuit 48.
Reference numeral 81 denotes a reference signal forming circuit made of, for example, a crystal oscillation circuit, in which a reference signal Sr with a frequency of 100 kHz is formed. Further, 82 is a phase comparison circuit, and 83 is a programmable divider, whose frequency division ratio 1/N is (i).
It can be changed according to N in the equation. That is, the frequency f7 of the signal S7 is the same as the signal S7 during AM reception.
,,2.7 to 31. corresponding to the frequency f,,f3 of S3.
It changes between 8MHz in 100kHz steps, and when receiving FM, it changes from 9 to 23MHz corresponding to the frequency of signal S.
Since the frequency division ratio 1/N is changed between 27 and 318 in 1 step, the frequency division ratio 1/N can be changed in 1 step between 27 and 318. Further, 84 is a latch circuit, 85 is a counter, and 87 is a timing circuit.

Then, the reference signal Sr from the forming circuit 81 is supplied to the timing circuit 87 and a gate pulse P having a predetermined pulse width is generated.
g is formed, and this pulse Pg causes the AND gate 8
6 is controlled, the beat signal S7 from the converter 47 is supplied to the counter 85 through the AND gate 86, and the frequency f of the signal S7 is counted by the counter 85.

Then, the count value of the counter 85 is determined by the latch circuit 84.
It is supplied to the divider 83 as a setting signal for its frequency division ratio of 1/N. In this way, the signal S7 from the converter 47 is frequency-divided into a signal with a frequency of 100 kHz by the divider 83, and this frequency-divided signal and the reference signal are connected to the comparator circuit 8.
2, the phase is compared, and the signal S8 is taken out.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an example of the present invention, FIGS. 2 and 3 are characteristic diagrams for explaining the same, and FIG. 4 is a system diagram of an example of a part of the circuit shown in FIG. 11 to 18 are AM reception systems, 31 to 36 are FM reception systems, 4
0A, 4 0B are PLL, 4 1, 4 6 are VF0,
42 is a fixed oscillation circuit. Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 includes a PLL, a fixed oscillation circuit, and a VFO, and
When receiving a frequency band of A second frequency conversion is performed as an oscillation signal, and when receiving the second frequency band, the output signal of the fixed oscillation circuit is supplied to the PLL, and the PLL
A receiver that performs frequency conversion using the output signal as a local oscillation signal.