JPS63212213A - Control voltage generating circuit for tuning - Google Patents

Abstract

PURPOSE:To improve a strong input characteristic by inputting an output of a tuning voltage generating circuit to a tap of a tuning coil and applying a power voltage to the cathode of a variable capacitor diode. CONSTITUTION:A high level power voltage Vcc is applied to the cathode of variable capacitor diodes VC1-VC3 and a tuning voltage in response to the output of a phase comparator 31 is applied to the tap of the coils L1-L3, that is, the anode side of the variable capacitor diode. Thus, even with a broadcast radio wave with a strong input given, no rectifier current flows to the variable capacitor diodes and no rectified voltage is caused. Thus, the local oscillation frequency is not pulled in by the rectified voltage even at a strong input, the AM suppression characteristic is improved, the distortion factor at the strong input is improved and the reception performance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a tuning control voltage generation circuit in a broadcast wave receiving system that includes a tuning circuit using a varicap diode.

[Summary of the Invention] The present invention provides a method for controlling the output of a tuning voltage generation circuit that generates a voltage according to the output of a phase comparator in a receiving system having a tuning circuit using a parallel circuit of two varicap diodes and a coil element. Receiving performance was improved by inputting the power supply voltage to the center tap of the coil element of the tuned circuit and applying it to the cathode side that connects the varicap diodes.

[Prior Art] In recent years, when receiving broadcast radio waves, a receiver equipped with an electronic tuning circuit using a varicap diode as a variable capacitance element (an element whose capacitance value changes depending on the magnitude of applied voltage) is used. method is becoming mainstream. This m
There are two child tuning reception methods.

One is the voltage synthesizer method as shown in Figure 3.
VCI, the varicap diode with the cathode connected,
It is equipped with a tuning circuit consisting of a parallel circuit of VO2, VO2 and coils LL, L2 and L3.

A voltage VT obtained by dividing the voltage VO of the stabilized power supply 1 with a volume VR is supplied to the connection point of this varicap diode via resistors R1, R2, and R3. Note that 2 is the antenna, 3 is the front end circuit, and 4 is the antenna.
is an intermediate frequency (IF) filter, and 5 is a time constant circuit.

In short, the method shown in Figure 3 changes the stabilized voltage Vo, which is the output of the stabilized power supply, with the volume VR, and uses the changed voltage vT as the variable voltage of the antenna, radio frequency (RF) circuit, and oscillator tuning circuit. cap diode to V
It is applied to the cathode sides of CI, VO2, and VO2 to change the tuning frequency. In this case, the tuning voltage VT is in an open loop, and changes in the tuning voltage are likely to directly lead to changes in the tuning frequency.

Therefore, it is common to add an automatic frequency control (AFC) circuit that extracts the audio output component and uses its output voltage to prevent out-of-tuning. Additionally, this method has the disadvantage that it is sensitive to temperature changes and tends to cause frequency shifts due to aging.

Another type of electronic tuning reception system is P as shown in Figure 4.
This is an LL synthesizer method.

This method divides the local oscillation frequency of the front end section 3 by passing the output of the front end section 3 through an oscillator buffer 6, a prescaler 7, and a divider 9 of a PLL circuit 8.
This divided frequency is compared with a reference frequency 11 by a phase comparator 10, and converted to the same frequency as the reference frequency to be compared. A voltage corresponding to the output is output from the tuning voltage generator 12.

The local oscillation frequency is controlled by an output signal that is applied to the cathode side of the varicap diodes of the three tuning circuits and corresponds to the phase difference between the 1-divided frequency and the reference frequency. This is a so-called servo system, and has the great advantage of automatically performing accurate reception using a PLL loop even if the local oscillation frequency shifts due to temperature changes, aging, etc. Note that instructions are given to the microcomputer 14 from the keyboard 13.

It is displayed on the frequency display 15, and the divider 9
is applied to set a predetermined frequency division ratio.

Further, the tuning voltage generating section 12 includes an active filter (LP).
F) and a bias voltage source, and the generated voltage changes depending on the signal from the phase comparator 10. The time constant of the LPF must be carefully determined because it has an important effect on the stability of the voltage applied to the varicap diode and the S/N ratio.

[Problems to be Solved by the Invention] In the above-mentioned tuning method using a varicap diode, the varicap diode has a unique rectifying effect, so the 1-strong input characteristic is poor, and this becomes a problem especially when the tuning voltage is low. The reason for this is as follows.

A varicap diode has a reverse voltage V between its cathode and anode, as shown in FIG.

is applied and the depletion layer is used to operate the capacitor, so the voltage on the cathode side must be higher than on the anode side.

However, when a broadcast radio wave is applied to this tuned circuit, the reverse voltage value between the cathode and anode changes instantaneously, but this broadcast radio wave is equal to the applied voltage V.

This is not a big problem as long as it is sufficiently small compared to It's going to change. In other words, the tuning frequency will shift.

Furthermore, when the broadcast radio waves become larger and become larger than the applied voltage vO as shown in Figure 6, the varicap diode instantaneously becomes a forward voltage, a forward current flows through the varicap diode, and the bias voltage is increased. It will also affect the tuning circuit of the oscillator through the resistor R (high resistance). In other words.

The current rectified by the varicap diode generates a rectified voltage by the bias resistance R, and this rectified voltage has an influence. As a result, there is a drawback that the local oscillation frequency is pulled in.

This is also a factor in the AM suppression degree deteriorating due to strong input. Therefore, it is desirable that the lowest potential applied to the varicap diode be as high as possible, but there is also a limit to this due to considerations with the receiving frequency range.

FIG. 7 shows a PLL synthesizer type tuning voltage generation section 12.
In this example, the local oscillation frequency of the front end section is input to the prescaler in the PLL block 8, and the frequency is divided by a certain integer (for example, 1/10). The frequency is divided into a frequency for comparison with a reference frequency using a predetermined frequency division ratio signal.

Then, the phases are compared with each other by the phase comparator 10, and the error voltage is sent to the next stage active filter (L P F).
7 tuning voltages are used to control the local oscillation frequency according to the error voltage. This tuning voltage is applied to the cathode side and the ground side of the varicap diode to form a reverse voltage. The reverse voltage between the cathode and the anode is normally set within a range of about 2 to 8V. Therefore, it is most vulnerable to strong input characteristics at the lowest potential of 2V.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tuning control voltage generation circuit that prevents the rectification effect of a varicap diode and improves the input characteristics even when a strong level broadcast wave is input.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a method for inputting the output of a tuning voltage generation circuit that generates a voltage according to the output of a phase comparator to the center tap of a tuning coil. A further feature is that the power supply voltage is applied to the cathode of the varicap diode of the tuning circuit.

[Function] In the present invention, a high level power supply voltage is applied to the cathode side of the varicap diode.

Even if a strong input broadcast radio wave is received, no rectified current flows through the varicap diode and no rectified voltage is generated, so the local oscillation frequency is not pulled in by the rectified voltage even with a strong input, and the A
The M suppression characteristic is improved, the distortion rate at strong input is improved, and the receiving ability is improved.

[Embodiments of the invention] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the receiving system according to the present invention, which relates to an improvement of the PLL synthesizer system.

In FIG. 1, 21 is a radio frequency (RF) amplifier;
22 is a mixer 235, an oscillator 24. A front end section consisting of an intermediate frequency (IF) amplifier 25, 26.27 an intermediate frequency (IF) filter, 28 an oscillator buffer, 29
is an oscillator amplifier, 30 is a prescaler, 31 is a PLL section, 32 is a controller consisting of a microcomputer,
33.34 is a stabilized power supply, 35 is an active filter (
LPF), 36 is the keyboard, 37 is the antenna, C1~
C3 is a capacitor. Also, as mentioned above, VCI
~VC3 is a varicap diode, L1 to L3 have coil tie, VCI, LL, C1t'7 antenna tuning circuit V
C2, I, 2. C2 is an oscillator tuning circuit, VO2, L3.
C3't' constitutes a radio frequency (RF) tuning circuit.

FIG. 2 shows an example of a specific configuration of the stabilized power supply 34 and active filter 35 shown in FIG.
4 is Zener diode Vz, capacitor C7, resistor R
6, the active filter 35 consists of transistors Q3. It consists of Q4, resistor R7°R8, and capacitors C8 and C9.

In the present invention, from the PLL section 31 to the active filter 35
The voltage VT passed through the tuned circuit is applied to the center tap of the coil of the tuned circuit, and the supply voltage Vec (for example, 10
v) is input to the cathode terminal of the varicap diode of the tuning circuit. In other words, the voltage at the cathode terminal of this diode was kept constant, and the voltage at the anode terminal was varied.

Therefore, the voltage between the anode and cathode is (Vcc-2)
If the voltage changes from ■ to (Vcc-8)V, and Vcc=10■, then the voltage changes from 8v to 2v.

Here, let's consider the reception frequency of changes in applied voltage.

In Japan, FM reception and reception frequency lines range from 76.1MHz to 89.1MHz.
The range is 9MHz.

The capacitance value of the Yap diode must be large as the receiving frequency is low. Therefore, the lower the voltage applied to the varicap diode, the lower the reception frequency. Therefore, the conventional applied voltage has changed from a low voltage to a high voltage, such as from 2v to 8v.

However, in the present invention, this relationship is reversed, so
We need to reverse our thinking. It's controller 3
2 microcomputer and computer software processing are sufficient. In other words, in the conventional method, when the applied voltage is 2V, 7
6. When receiving IMHz, 89.9MHz is received when the voltage is 8V, whereas in the method of the present invention, it is 89.9MHz when the voltage is 2V.
z, and when it is 8■, 76, IMHz is received, which is the opposite of the conventional method. Therefore, there is a problem that the actual display frequency and reception frequency are different, so the software changes the frequency from 76.1MHz to 89.9MHz, 89.9M
All you have to do is change the display frequency from Hz to 76 and IMHz.

Further, when performing a tuning operation, it is necessary to operate the tuning switch on the keyboard 36 and perform software processing to reverse the functions of manual up/down and auto tuning up/down.

[Effects of the Invention] As described above, according to one embodiment of the present invention, a high level power supply voltage Vcc is applied to the cathode side of the varicap diode.
is applied, and a tuning voltage according to the output of the phase comparator is applied to the middle tap of the coil, that is, the anode side of the varicap diode, so even if a strong input broadcast radio wave is received, a rectified current will not flow to the varicap diode. Therefore, no rectified voltage is generated. As a result, the rectified voltage does not pull in the local oscillation frequency even with a strong input, improving AM suppression characteristics, improving the distortion rate at a strong input, and improving reception performance.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of a reception system including a tuning control voltage generation circuit according to the present invention, FIG. 2 is a diagram showing a specific configuration of a part of FIG. 1, and FIGS. 3 and 4 are conventional FIGS. 5 and 6 are explanatory diagrams of the conventional reception system, and FIG. 7 is a specific configuration diagram of the tuning voltage generation section of FIG. 3. . VCI~VC3...Varicap diode, L1~
L3...Fist coil, Vcc...Power supply voltage, 31...PLL section. 35...Active filter. Patent applicant: Clarion Co., Ltd. Figure 3 Figure 4 Figure 6 Figure 6

Claims (1)

[Claims] A tuned voltage generation circuit that generates a voltage according to the output of a phase comparator in a broadcast radio reception system, which is equipped with two varicap diodes whose respective cathodes are connected to each other, and a tuned circuit in which a coil element is connected in parallel. input the output to the intermediate tap of the coil element of the tuned circuit, and
A control voltage generation circuit for tuning, characterized in that a power supply voltage is applied to a cathode of a varicap diode of the tuning circuit.