JPH0298209A - Electronic tuning circuit for fm receiver and its tracking adjusting method - Google Patents

Abstract

PURPOSE:To reduce number of components of an electronic tuning circuit by adjusting an inductance of a variable tuning coil of a tuning circuit nearly in the middle of an FM reception band and providing only one tracking adjustment point making the tracking error nearly zero. CONSTITUTION:In the tracking adjustment, the inductance of an oscillation coil Lo is adjusted while a maximum tuning voltage is applied to a varactor diode VDD of a local oscillation circuit 7 from a PLL circuit 8 so that an intermediate frequency is added to a reception frequency being a maximum oscillated frequency of the local oscillation circuit 7. Then the inductance of the tuning coil L4 of the antenna tuning circuit 2 is adjusted nearly in the middle of the FM reception band to make the tracking error zero. Thus, a trimmer capacitor for tracking adjustment of the electronic tuning circuit is saved.

Description

[Detailed Description of the Invention] [Industrial Application Field of the Invention] The present invention relates to an electronic tuning circuit for an FM receiver using a variable capacitance diode, and the number of components for tracking adjustment is reduced to simplify the tracking adjustment. This relates to an electronic tuning circuit.

[Prior art]

Conventionally, in an FM receiver, tracking adjustment is performed so that the tracking error is minimized at two points in the reception band (low frequency side FA + high frequency side Fl) as shown in FIG. Normally, after the local oscillator circuit is adjusted, the low frequency side FA of the receiving band is adjusted using the tuning coil of the tuning circuit so that the tracking error becomes zero, and then the high frequency side F1 is adjusted by tuning the trimmer capacitor of the tuning circuit. The capacitance is adjusted so that the tracking error becomes zero. That is, a variable tuning coil and an expensive trimmer capacitor are used as components for tracking adjustment.

In addition, in electronic tuning circuits using variable capacitance diodes, changes in the tuning capacitance of the variable capacitance diodes and tuning voltage ■
7 has a logarithmic characteristic, a tracking error will theoretically occur and it is impossible to avoid the tracking error.
An electronic tuning circuit for an FM receiver that minimizes errors is desired.

[Problem to be solved by the invention]

In the electronic tuning circuit of an FM receiver using a variable capacitance diode, a tracking adjustment component is used, and the tuning circuit includes:
A trimmer capacitor is used as a variable tuning coil and tuning capacitor.

Usually, the tuning coil can be constructed from an inexpensive spring-like coil whose inductance value can be adjusted by adjusting the width of the coil. However, trimmer capacitors have the disadvantage that they are relatively expensive components, making the electronic tuning circuit expensive to manufacture. In addition, the inclusion of a large number of tuning coils and trimmer capacitors, which are tracking adjustment parts, increases the rate at which the tracking error value exceeds the control limit during the tracking adjustment process.Therefore, to reduce manufacturing costs, it is necessary to It is necessary to reduce the number of parts as much as possible to reduce tracking adjustment man-hours.

The present invention has been made to solve the above-mentioned problems, and its main purpose is to provide an electronic FM receiver equipped with a tuning circuit capable of tracking adjustment at one point approximately in the center of the FM reception band. To provide a tuned circuit.

Another object of the present invention is to provide an inexpensive electronic tuning circuit for an FM receiver by reducing the number of components in the electronic tuning circuit.

Furthermore, another object of the present invention is to provide a tracking adjustment method for an electronic tuning circuit of an FM receiver that has a simple adjustment process, and to provide an electronic tuning method for an FM receiver that can simplify the tracking adjustment process and reduce manufacturing costs. To provide the circuit.

[Means to solve problems]

The electronic tuning circuit of the FM receiver of the present invention uses a PLL synthesizer method to provide a tuning voltage of V? is set and supplied to the electronic tuning circuit, and a desired broadcast wave is selected. An electronic tuning circuit is composed of a tuning circuit and a local oscillation circuit, and these tuning circuits and local oscillation circuits use two variable capacitance diodes that share a common cathode, and a PLL is connected to these variable capacitance diodes. Tuning voltage Vt through the circuit
is supplied. Tracking adjustment is performed by adjusting the inductance value of the oscillation coil with the maximum tuning voltage V TNAX applied from the PLL circuit to the variable capacitance diode of the local oscillation circuit, so that the oscillation frequency of the local oscillation circuit reaches the maximum reception frequency FMAM. and the intermediate frequency FIN is added to the frequency f, and then adjust the inductance value of the tuning coil of the antenna tuning circuit or high frequency tuning circuit at approximately the center of the FM reception band so that the tracking error becomes zero. Adjust accordingly. By using such a tracking adjustment method, a trimmer capacitor and an antenna tuning circuit for adjusting the oscillation frequency of the local oscillator circuit,
The high frequency tuning circuit does not require a trimmer capacitor for tracking adjustment.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of an electronic tuning circuit of an FM receiver according to the present invention, which includes an electronic tuning circuit using two variable capacitance diodes with a common cathode. , is an FM receiver whose tuning voltage is preset using a PLL synthesizer method.

1 is an antenna, 2 is an antenna tuning circuit, 3 is a Takaoka wave amplification circuit, 6 is a mixing circuit, 7 is a local oscillation circuit, 8 is a PLL
9 is a buffer circuit, and 10 is a terminal to which a program signal for selecting a predetermined receiving frequency is applied. The antenna tuning circuit 2 includes a spring-shaped variable tuning coil LA and a fixed tuning capacitor C that are connected in parallel.
It is constructed by connecting the anodes of Sa and two variable capacitance diodes V and ^ whose cathodes are commonly connected to the other end of the tuning coil Lk. Further, the local oscillation circuit 7 includes a variable oscillation coil LO1, a fixed oscillation capacitor C8°, and two variable capacitance diodes ■. . The antenna tuning circuit 2 is constructed from connections similar to those of the antenna tuning circuit 2. In these circuits, conventional trimmer capacitors are not used as tuning and oscillation capacitors. In addition, tuning coil L
a does not need to be a spring-like variable coil,
It is clear that a coil using a magnetic core may be used, and the same applies to the oscillation coil L0.

A predetermined frequency f1 of the broadcast wave input from the antenna 1 is selected by the antenna tuning circuit 2, amplified by the high frequency amplification circuit 3, and supplied to the mixing circuit 6. On the other hand, the local oscillation frequency f2, which is the output of the local oscillation circuit 7, is supplied to the mixing circuit 6. The zero local oscillation frequency ft is supplied to the PL and L circuits 8 via the buffer circuit 9, and the PLL circuit 8
A tuning voltage V is supplied to the connection point of the variable capacitance diode VDO of the local oscillation circuit 7 and the connection point of the variable capacitance diode VIIA of the antenna tuning circuit 2, respectively, for tuning. A program signal corresponding to a desired reception frequency is supplied from the terminal 10.

In the tracking adjustment method in the electronic tuning circuit of an FM receiver according to the present invention, the local oscillation circuit 7 has a maximum tuning voltage V TM set by the PLL synthesizer method.
With AX applied, that is, the variable capacitance diode ■
,. Tracking adjustment is performed after the oscillation coil L0 is adjusted in advance at the point where the capacitance becomes the minimum. The local oscillation frequency f2 of the local oscillation circuit 7 is determined by the variable capacitance diode V.
,. While the maximum tuning voltage VTNAX is applied to the oscillation coil, the inductance value of the oscillation coil is adjusted so that the oscillation frequency becomes the sum of the maximum reception frequency FWAM and the intermediate frequency FIN. After performing this adjustment process, a tracking adjustment process begins. In the tracking adjustment step, the inductance value of the tuning coil LA of the antenna tuning circuit 2 is adjusted at a frequency approximately in the middle of the FM reception band so that the tracking error becomes approximately zero.

FIG. 2 is another embodiment of an electronic tuning circuit for an FM receiver according to the present invention.

In the embodiment shown in FIG. 2, in addition to the embodiment shown in FIG.
are connected, and the rest is constructed of the same circuit as the embodiment shown in FIG. The high frequency tuning circuit 4 includes a variable tuning coil, an R1 tuning capacitor Cs*-, and two variable capacitance diodes. are connected in the same configuration as the antenna tuning circuit 2. Furthermore, the local oscillation circuit 7 in FIG. 2 also includes a variable oscillation coil L0 similar to the antenna tuning circuit 2.
A fixed oscillation capacitor C8 and two variable capacitance diodes VDO are connected. These circuits do not use trimmer capacitors as tuning capacitors or oscillation capacitors, as in the embodiment shown in FIG.

The oscillation output of the local oscillation circuit 7 is supplied to the mixing circuit 6 and also to the PLL circuit 8 via the buffer circuit 9, and the tuning voltage 7 from the PLL circuit 8 is applied to the variable capacitor of the local oscillation circuit 7. The signal is supplied to the connection point of the diode VOO and to the connection points of the variable capacitance diodes VDA+VDI of the antenna tuning circuit 2 and the high frequency tuning circuit 4, respectively. A program signal corresponding to a desired reception frequency is supplied from the terminal 10.

Tracking adjustment in the embodiment shown in FIG. 2 is performed in the same manner as in the embodiment shown in FIG. 1, and after adjusting the local oscillation circuit 7 in advance,
In the tracking adjustment process, the inductance values of the tuning coils La and Lm of the antenna tuning circuit 2 and the high frequency tuning circuit 4 are adjusted at a frequency approximately in the middle of the reception band so that the tracking error becomes zero.

Incidentally, throughout FIG. 1 and the second embodiment, the antenna tuning circuit 2. High frequency tuning circuit 4. and variable capacitance diodes Voa, Vwa, used in the local oscillation circuit 7.

The capacitors C8 and C8 are bypass capacitors.

[Effect]

The operation of the electronic tuning circuit of the FM receiver of the present invention and its tracking adjustment process will be explained based on the diagrams showing the tracking curves of FIGS. 3 and 4.

3 and 4 illustrate the occurrence of tracking errors in the electronic tuning circuit of the FM receiver of the present invention. Figure 3 shows Japan's FM reception band of 76MHz to 9.
Figure 4 shows the tracking curve for the 88MHz to 108MHz band, which is the FM reception band in the United States, and shows the tracking lag error in the optimal and worst cases, respectively, within a range where practical sensitivity is sufficient. An example is shown.

The tracking curve (11(2) (3
) will be explained below. The tracking curve (1) in FIG. 3 is the circuit constant for the optimum embodiment, and the tracking curves (2) and (3) in FIG. 3 are examples for the worst case. Tracking curve (1) in Figure 3
Table 1 shows the circuit constants of the embodiments (2) and (3).

The tracking curve (1) in Figure 3 shows the variable capacitance range of variable capacitance diode DA, tuning capacitor C3A, tuning coil La + oscillation capacitor C5°, and oscillation coil L.
The circuit constants of 0 are set as shown in column (1) of Table 1. Note that the oscillation coil L0 is set in the oscillation frequency adjustment step, and the tuning coil LA is adjusted to this value in the tracking adjustment step.

Tracking curves (2) and (3) in FIG. 3 are examples of the worst tracking error, and the circuit constants at that time are as shown in Table 1. The capacitance of the variable capacitance diode is shown in (2) of Table 1, and the maximum tuning voltage VT is 23.79F at ^8, and the minimum tuning voltage V? M.I.
The tuning capacitance is lower at each point than the value of 11.0 pF in the optimal embodiment, and the tracking curve (2) in Figure 3 shows that the variable capacitance range of the variable capacitance diode reaches its maximum downward. This is a case of fluctuation.

Further, the tracking curve (3) in FIG. 3 is a case where the variable range of the capacitance of the variable capacitance diode changes upward to the maximum. The variable capacitance diode ■ used in the example is:
8v is supplied from the PLL circuit 8 as the maximum tuning voltage VTHkX, 1v is applied as the minimum tuning voltage VTMIN, and the minimum capacitance CHI and maximum capacitance at that time are CMAI.
It shows.

The characteristics of a variable capacitance diode are such that it is difficult to always obtain a constant tuning capacitance unless strict characteristics are selected. Maximum tracking
Tracking of normal electronic tuned circuits within error
Indicates that an error has occurred. The tracking adjustment is performed so that the inductance value of the tuning coil LA of the antenna tuning circuit 2 becomes zero at 33 MHz, which is approximately the center of the FM reception band of 76 MHz to 90 MHz.

Tracking adjustment is performed by adjusting the variable tuning coils La, La of the antenna tuning circuit or high frequency tuning circuit, but the oscillation capacitor C3° is set to - from the design value.
The tuning capacitor CSA has a value 5% higher than the circuit constant of the optimum embodiment. The oscillation capacitor C8° and the tuning capacitor CSa are set to a value of ±5% of the circuit constant of the optimum embodiment.

On the other hand, the variable capacitance diode VD required for such reception band
A, V. . The minimum capacitance change ratio can be found from the following equation.

f + sax ” / f aha ” = CmaX
/ C, I! 1% '-'-'-' (11 (however, f
l + a ) Japan's FM reception band 76 MHz to 90 MHz
The change ratio in the case of z is determined as follows (based on equation 11).

f ma, l"/f, = 11" = 1.40
2−・−=−−−−−−(2) Therefore, the capacitance range of the variable capacitance diode must be greater than this value, and the capacitance change ratio of the variable capacitance diode ■DA in (1) of Table 1 is , based on equation (1), CMAX/CMIN ”q
It is found to be 2.077. Also, when similarly calculated for the case (2) of Table 1, the capacitance change ratio is 2.227,
In the case of (3) in Table 1, the capacitance change ratio is determined to be 2.020. Therefore, it is possible to obtain a sufficient variable capacity ratio.

As is clear from Figure 3, the tracking frequency is 90
The maximum tracking error occurs at M)lz, but since the range is approximately 260 KHz to -600 KHz, sufficient practical sensitivity can be obtained. It is clear that the practical sensitivity can be further improved by providing a two-stage tuning circuit as in the embodiment shown in FIG.

Next, the FM reception band in the United States will be explained based on FIG.

The tracking curve +11 (2) (3) in Figure 4 is
Tracking curve (1) shows the optimum embodiment, and tracking curve (21(3)) shows the embodiment in which the tracking error is the worst. The circuit constants of these embodiments are shown in Table 2.

Table 2 (Circuit constants of electronic tuning circuit) The range of capacitance change of variable capacitance diode ■DA is compared with the case of +11 in Table 2 showing the circuit constants of the tracking curve (1) in Figure 4, which is the optimum embodiment. Therefore, the circuit constants of the example in (2) of Table 2 fluctuate downward, and the circuit constants of the example in (3) of Table 2 fluctuate downward.
In this embodiment, the circuit constants are varied upward. Table 2 (1
) is an optimum embodiment in which the tracking error is minimized, and the capacitance change range of the variable capacitance diode varies within a range of 13.0 pF to 27° OpF. The circuit constants of the embodiment with the worst tracking error are shown in (2) and (3) of Table 2.
), the variable capacitance diode VCD is 11.0
The range of pF to 24.5 pF was varied, and (
3), but 15. It fluctuates in the range of OpF to 30.3 pF. The tracking curve of the electronic tuning circuit according to the circuit constants of the embodiments (2) and (3) in Table 2 is shown in (2) in FIG.
) (3). Note that variable capacitance diodes used in the tuning circuit and the local oscillation circuit have the same characteristics.

The FM reception band is 88 MHz to 108 MHz, and the capacitance change ratio of the variable capacitance diode required for reception in this band is (from equation 11, f vhsx ” / f −hin ” #1.51
To request W) Rarel.

In the example (1) of Table 2, the capacitance change ratio is calculated from equation (1) as C, -X/C-i, ''-2,077. In the example, the capacitance change ratio is determined to be 2,227, and in the case of (3) in Table 2, the capacitance change ratio is 2.227.
It is calculated as 02. This shows that it is possible to obtain a sufficient variable capacity ratio.

The tracking adjustment is performed by adjusting the inductance value of the tuning coil La of the tuning circuit to 9, which is approximately the center of the reception band in the United States.
8M1lz, the tracking error was adjusted to zero, and the circuit constants in that case are shown in Table 2. Also, oscillation capacitor C5°.

The tuning capacitor CSA is ±5 of the circuit constant of the optimum embodiment.
Set the value to %.

In the US FM reception band, as shown in Figure 4, the tracking error is maximum at 108 MHz and 85 MHz.
0 K) lz to -400 KHz, which is a value that provides sufficient practical sensitivity.

As mentioned above, as is clear from FIGS. 3 and 4, even in the worst case of tracking error, practically sufficient sensitivity can be obtained. It is clear that the practical sensitivity of the negative layer is improved by providing two stages of thermal and tuning circuits.

〔effect〕

Even if the variable range of the capacitance of the variable capacitance diode varies within the range shown in Tables 1 and 2, the electronic tuning circuit of the FM receiver of the present invention can be used without using a trimmer capacitor for the tuning capacitor or the oscillation capacitor. By adjusting the inductance value of the tuning coil provided in the tuning circuit, it is possible to obtain a sufficient practical sensitivity without any practical problems, making it extremely practical.

In addition, optimal tracking adjustment can be obtained by simply adjusting the tracking error to zero at a frequency approximately in the middle of the receiving band, making it possible to provide an electronic tuning circuit for an FM receiver with extremely simple adjustment steps. There are advantages.

Furthermore, since the trimmer capacitor, which is a component for tracking adjustment of the electronic tuning circuit, can be eliminated, the parts cost and manufacturing cost of the electronic tuning circuit can be reduced, and there is an advantage that FM receivers can be supplied at low cost. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of an electronic tuning circuit of an FM receiver according to the present invention, FIG. 2 is a block diagram showing another embodiment, and FIG. 3 is a block diagram showing an FM receiver according to the present invention. FIG. 4 is a diagram showing the tracking error of the electronic tuning circuit of an FM receiver in the Japanese reception band according to the present invention, and FIG. FIG. 5 is an explanatory diagram of tracking adjustment of an electronic tuning circuit of a conventional FM receiver. 1: Antenna, 2: Antenna tuning circuit, 3.4: High frequency amplifier circuit, 5: High frequency tuning circuit, 6: Mixing circuit, 7: Local oscillation circuit, 8: PLL circuit. 9: Buffer circuit, 10: Terminal

Claims (2)

[Claims] (1) In an electronic tuning circuit of an FM receiver using a variable capacitance diode that is supplied with a tuning voltage by a PLL synthesizer method and tunes to a desired broadcast wave, the electronic tuning circuit has an approximately maximum tuning voltage. The tuning circuit includes a local oscillation circuit adjusted to have the maximum oscillation frequency under applied conditions, and the tuning circuit has a variable tuning coil connected in parallel with a fixed tuning capacitor, and the cathodes of which are connected in common. The anodes of the first and second variable capacitance diodes are connected to the other ends of the tuning coil, and the inductance value of the variable tuning coil of the tuning circuit is adjusted approximately at the center of the FM reception band. F characterized by having one tracking adjustment point that makes the tracking error approximately zero.
M receiver electronic tuning circuit. (2) In a method for adjusting an electronic tuning circuit of an FM receiver using a variable capacitance diode that is supplied with a tuning voltage by a PLL synthesizer method and tuned to a desired broadcast wave, the oscillation frequency of the local oscillation circuit is an adjustment step in which the oscillation frequency is adjusted to be the maximum oscillation frequency obtained by adding the intermediate frequency to the reception frequency while the maximum tuning voltage is applied; and after the adjustment step, the tuning circuit is adjusted at approximately the center of the FM reception band; Tracking is performed by adjusting the inductance value of the tuning coil.
1. A tracking adjustment method for an electronic tuning circuit of an FM receiver, comprising a tracking adjustment step that reduces errors to approximately zero.