JP2694763B2 - Coil for voltage controlled oscillator and voltage controlled oscillator using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coil used to oscillate a fundamental frequency of a voltage controlled oscillator and a voltage controlled oscillator using the coil.

[0002]

2. Description of the Related Art A voltage controlled oscillator (hereinafter referred to as VCO) used in a phase locked loop circuit (hereinafter referred to as PLL) is formed in an IC, but a coil which is a circuit element that oscillates a fundamental frequency is an IC. Connected to the outside of. FIG. 3 is a wiring diagram of a conventional coil for a voltage controlled oscillator, but the coil 10 for a voltage controlled oscillator is a capacitor 1
1 is connected in parallel, and terminals 12 and 13 at both ends are connected to VCO 14.

The intermediate frequency signal of the video signal of the television is PL
When detecting using L, the parallel circuit of the coil 10 and the capacitor 11 is the same as the intermediate frequency in Japan, 58.7.
It is configured to oscillate at 5 MHz. However, VCO
From 14, harmonics of the fundamental frequency are likely to be generated, which is particularly inconvenient when the video signal of the television is detected by using the PLL. This is because there are four TV channels in the vicinity of 176 MHz, which is a triple harmonic, and interference often occurs in the receiver, often causing an image disturbance.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a coil for a voltage controlled oscillator which can prevent the generation of harmonics of the fundamental frequency mainly from the voltage controlled oscillator.

[0005]

A coil for a voltage controlled oscillator according to the present invention is connected in parallel with a capacitor, and taps connected to the voltage controlled oscillator are provided in the vicinity of both ends thereof, and substantially equal inductances are provided on both sides of the capacitor. It is characterized in that they are equivalently connected in series.

An embodiment of a coil for a voltage controlled oscillator according to the present invention will be described below with reference to FIGS. 1, 2 and 6. 1 is a connection diagram, FIG. 2 is an equivalent circuit diagram, and FIG. 6 is a specific circuit diagram of a voltage controlled oscillator. The coil 1 for a voltage controlled oscillator of the present invention is connected in parallel with the capacitor 2, but taps T ₁ and T ₂ are provided near both ends of the coil 1 and are connected to the terminals 3 and 4, respectively. Terminal 3 and terminal 4
Is connected to the differential amplifier that constitutes the VCO . And
The coil 1 and the capacitor 2 serve as a load of the differential amplifier.

The inductance between the end of the coil 1 and the tap T ₁ and the inductance between the other end of the coil 1 and the tap T ₂ are equal. The coupling coefficient between the coupling coefficient, the other end portion and taps T ₁ than tap T ₂ of the coil 1, the tap T ₂ of the between coil portion and taps T ₁ of the end than tap T ₁ of the 1, tap T ₂ Are equal.

From such a coil 1, as shown in FIG. 2, three inductances L ₁ , L ₂ and L ₃ are obtained. The inductance L ₁ is obtained by the coil 1 between the taps T ₁ and T ₂ . The inductance L ₂ and the inductance L ₃ are formed on both sides of the tap T _1, that is, the tap T _1.
2 are obtained by coupling both sides sandwiching ₂ and are equivalently connected to both sides of the capacitance C of the capacitor 2.

Under the above conditions, the inductance L ₂
And the inductance L ₃ are equal. Further, the inductance L ₂ and the inductance L ₃ are smaller than the inductance L ₁ . The equivalent circuit of FIG. 2 causes parallel resonance due to the inductance L ₁ and the capacitance C, and series resonance due to the inductances L ₂ and L ₃ and the capacitance C.

Parallel resonance frequency f _P and series resonance frequency f _D
Are expressed by equations (1) and (2), respectively. f _P = 1 / 2π (L ₁ · C) ^1/2 (1) f _D = 1 / 2π (L · C) ^1/2 (2) where L = L ₂ + L ₃ ≈2L ₂ ≈2L ₃ is there. The impedance between the terminals 3 and 4 becomes maximum at the frequency f _P and becomes minimum at the frequency f _D.

That is, the equivalent circuit of FIG. 2 has a trap frequency f _D between the terminals 3 and 4 where the signal near the frequency f _P is not attenuated but the signal is attenuated. FIG. 4 shows an example of a filter characteristic diagram of a coil for a voltage controlled oscillator of the present invention connected in parallel with a capacitor. The frequency f _P is set to 58.75 MHz, but the trap frequency exists at a frequency slightly lower than 180 MHz. This trap frequency almost matches the triple harmonic of 58.75 MHz.

In this case, the total number of turns of the coil 1 is 7 turns, and the taps T ₁ and T ₂ are provided at positions of 1/2 turn from both ends of the coil 1, respectively. The capacitance C is 22 pF and the stray capacitance is 5 pF. The trap frequency can be changed by changing the positions of the taps T ₁ and T ₂ . FIG. 5 is a filter characteristic diagram of a conventional coil for a voltage controlled oscillator, which has no tap and is connected in parallel with a capacitor, but has a trap frequency of 3
It does not exist near the frequency of the double harmonic.

The characteristic diagram of FIG. 5 shows the case where the number of turns of the coil 10 of FIG. 3 is the same as the number of turns of the coil 1 and the capacitance of the capacitor 11 is the same as the capacitance of the capacitor 2. The self-resonance due to the inductance component occurs in the vicinity of 400 to 500 MHz, and a natural trap frequency exists. But,
This frequency cannot be controlled freely and cannot be used as a trap frequency.

The coil of the present invention can prevent the generation of its own harmonic by matching the trap frequency with the frequency of the higher harmonic of the fundamental frequency, and even if the higher harmonic is generated inside the VCO, the higher harmonic is generated. Since the waves can be absorbed, there is almost no generation of harmonics outside the VCO. In the coil 1 of the embodiment, the inductances L ₂ and L ₃ equivalently connected to both sides of the capacitor 2 are made equal, but this is because the VCO circuit is a combination of differential circuits, so that the differential circuits are balanced. This is because it does not collapse, and the inductance may be slightly different as long as the balance of the differential circuit is not disturbed.

FIG. 6 shows a voltage controlled oscillator coil 1 to which the capacitor 2 of FIG.
3 is a specific circuit diagram of the voltage controlled oscillator connected to 01. FIG. The first and second transistors 102 and 103 that form the differential amplifier 101 are connected to each other in a positive feedback loop, and the voltage controlled oscillator coil 1 that is connected in parallel with the capacitor 2 is connected as each load. Therefore, it is possible to oscillate at the fundamental frequency determined by the capacitor 2 and the voltage controlled oscillator coil 1, and suppress the harmonic component thereof.

A control signal for adjusting the oscillation frequency is applied to the control terminals 104 and 105 of FIG. The control signal increases or decreases the collector DC potential of the first control transistor 106 to change the gain of the differential amplifier 101, and as a result, the oscillation frequency can be slightly changed. The second control transistor 107 and the transistors 108 and 109 are
This is for making the collector DC currents of the first and second transistors 102 and 103 constant, and the oscillation output is obtained at the output terminals 110 and 111.

A conventional voltage controlled oscillator is used as a P receiver for a television receiver.
When used in a detection circuit using LL, it was necessary to store the entire configuration of FIG. 3 including the coil for the voltage controlled oscillator in the shield case and then install it in the television receiver. If such a voltage-controlled oscillator is used in a similar detection circuit, the shield case becomes unnecessary, which leads to downsizing of the detection circuit and cost reduction.

[0018]

As described above, the coil for a voltage controlled oscillator of the present invention is provided with taps in the vicinity of both ends thereof so that inductance can be equivalently obtained on both sides of a capacitor connected in parallel. Then, the circuit for oscillating the fundamental frequency is configured in combination with the IC for the voltage controlled oscillator, and the trap frequency that coincides with the frequency of the harmonic wave is formed, so that generation of the harmonic wave from the VCO can be prevented.

Although such a coil can be widely used in a PLL, it is highly practical especially when the intermediate frequency signal of a video signal of a television is detected using the PLL. Since the voltage-controlled oscillator using the coil of the present invention does not require a shield case, it is of course necessary to downsize itself and reduce cost, and there is an advantage that leads to downsizing of the detection circuit and cost reduction.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of a coil for a voltage controlled oscillator according to the present invention.

FIG. 2 is an equivalent circuit diagram of FIG.

FIG. 3 is a wiring diagram of a conventional voltage controlled oscillator coil.

FIG. 4 is a filter characteristic diagram of a coil for a voltage controlled oscillator according to the present invention.

FIG. 5 is a filter characteristic diagram of a coil for a conventional voltage controlled oscillator.

FIG. 6 is a circuit diagram showing a voltage controlled oscillator of the present invention.

[Explanation of symbols]

1 Voltage controlled oscillator coil 2 Capacitor T ₁ tap T ₂ tap

Claims (2)

(57) [Claims] 1. A capacitor is connected in parallel, and two taps connected to a differential amplifier forming a voltage controlled oscillator are provided in the vicinity of both ends, and inductances which are substantially equal to each other are equivalent between the capacitor and the two taps. A coil for a voltage controlled oscillator, wherein a trap frequency for a harmonic of a fundamental frequency of the voltage controlled oscillator is set by an inductor connected in series to the capacitor and an inductance equivalently connected to both sides of the capacitor. 2. A voltage controlled oscillator coil, which is connected in parallel with a capacitor, has two taps provided in the vicinity of both ends thereof, and has substantially the same inductance and is connected in series equivalently between the capacitor and the two taps. A differential amplifier having emitters connected in common and a collector connected to the tap, the differential amplifier comprising:
A capacitor and an inductor equivalently connected to both sides of the capacitor
Voltage controlled oscillator
By matching the harmonic frequency of the fundamental frequency of
Ri, the voltage controlled oscillator, characterized in that reduced the generation of harmonic components of the fundamental frequency.