JPH0611087B2 - Voltage controlled oscillator - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a voltage controlled oscillator circuit.

[Technical background of the invention]

For example, in a color television receiver, an automatic phase control (hereinafter referred to as APC) circuit is used as a color synchronizing circuit. This APC circuit requires a highly accurate voltage controlled oscillator (hereinafter referred to as VCO).
Fig. 4 shows the VCO circuit diagram, and Fig. 5 shows the vector relation diagram.

In FIGS. 4 and 5, the signal () output from the resonator 11 is phase-shifted by the phase shift circuit 12φ ₁ to become the signal (). The signal () and the signal () are combined by the combining circuit 13 to become the signal (). This signal () is given to the resonator 11 via the amplifier circuit 14,
An oscillation operation is performed by being delayed by φ _{3 by the} resonator 11.

In FIG. 4, reference numeral 15 is an APC detection circuit that detects the phase difference between the burst signal (Bu) and the signal () and obtains a voltage signal that controls the combining ratio of the combining circuit 13.

[Problems of background technology]

In the VCO having such a configuration, the fluctuation of the phase shift amount of the phase shift circuit 12 leads to the fluctuation of the frequency variable range. Therefore, in order to obtain a stable frequency variable range, a highly accurate phase shift circuit is required.

The phase shift characteristic of the phase shift circuit is greatly influenced by the fluctuation of the characteristics of the elements that compose it. The characteristics of the element are much less accurate in an integrated circuit (hereinafter referred to as IC) than in individual components. Therefore, conventionally, VCO
In this case, the phase shift circuit 12 is incorporated as an external circuit.

However, this has a problem that the number of pins of the IC increases, and considering the manufacturing cost, etc.
Was requested.

[Object of the Invention]

The present invention has been made to address the above circumstances,
An object of the present invention is to provide a VCO suitable for use in an IC, in which a predetermined frequency variable range does not change even if the element characteristics change.

[Outline of Invention]

The present invention provides a first impedance element having one of resistance and reactance, one end of which is connected to an input terminal to which an input signal having a predetermined frequency is supplied, and the other end of the first impedance element. A series circuit of a resistive impedance element and a reactance impedance element connected between a reference potential point is included, and the input signal is phase-shifted by a predetermined phase amount at a connection point of the first impedance element and the series circuit. A phase shift circuit for obtaining a second signal that has
Signals are respectively supplied, and an amplitude limiting circuit having a differential amplifier circuit configuration for limiting and outputting the amplitudes of these signals is provided,
The input signal whose amplitude is limited and the second signal are appropriately combined in accordance with the voltage for phase restriction, and a combining circuit for outputting the combined signal to the output terminal is provided, and resonance is provided between the output terminal and the input terminal. And a value such that the fluctuation amount of the phase shift amount becomes smaller than the fluctuation amount of the impedance ratio of the resistive impedance element and the reactance impedance element that form the series circuit of the phase shift circuit. The impedance element constant is set.

Example of Invention

An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, the signal () passing through the crystal vibration sensor 21 is I
It is given to the pin 23 of C22, and the input terminal 2 of the phase shift circuit 24 is fed from this pin 23 through the transistor Q _11.
41. The phase shift circuit 24 receives the input signal ()
Is delayed by φ _5, and a signal () is obtained at its output terminal 242. This () is given to the bases of the transistors Q ₁₇ and Q ₂₀ of the amplitude limiting circuit 25 via the transistor Q ₁₂ . The input signal () of the phase shift circuit 24 is given to the bases of the transistors Q ₁₃ and Q ₁₆ of the amplitude limiting circuit 25 via the transistor Q ₂₁ . The transistors Q ₁₄ , Q ₁₅ , Q ₁₆ , and Q of this amplitude limiting circuit 25
The base of ₁₉ has a transistor Q from a constant voltage source V _11.
A DC bias is applied via ₂₂ and Q ₂₃ .

In the amplitude limiting circuit 25, the transistors Q ₁₇ , Q
Reference numeral ₁₈ constitutes a differential amplifier circuit using I ₁₃ as a constant current source. The transistors Q ₁₉ and Q ₂₀ form a differential amplifier circuit using I ₁₄ as a constant current source. Therefore, the signal output from the phase shift circuit 24 () by the amplitude limiting action of the differential amplifier circuit, a constant amplitude of the signal is outputted to the collector of the transistor Q ₁₇ to Q _20. That is, the amplitude level of the signal appearing at the collector of the transistor _Q 17 _{to Q 20} is proportional to the current amount of the constant current source _{I 13, I 14,} does not depend on the amplitude level of the phase shift circuit 24. This is the signal () that is the other input of the amplitude limiting circuit 25.
The same applies also to the above, because of the amplitude limiting action of the operation amplification circuits of the transistors Q ₁₃ and Q ₁₄ having I ₁₁ as a constant current source and the operation amplification circuits of the transistors Q ₁₅ and Q ₁₆ having I ₁₂ as a constant current source, the signal ( ) Is output from the collectors of the transistors Q _{13 to} Q ₁₆ as a signal having a constant amplitude.

Output signal of the amplitude control circuit 25 that has been subjected to the amplitude limiting action
Is supplied from the collector of the transistor Q ₁₈ to the emitters of the transistors Q ₂₄ and Q ₂₅ of the combining circuit 26.
Further, the output signal of the amplitude control circuit 25 subjected to the amplitude limiting action is supplied to the emitters of the transistors Q ₂₆ and Q ₂₇ of the synthesizing circuit 26. Further, the input / output signals () and () of the phase shift circuit 24 are combined at the common connection point of the collectors of the transistors Q ₁₃ and Q ₁₉ , and are supplied to the emitter of the transistor Q ₂₃ . An output signal of the phase shift circuit 24 appearing at the collector of the transistor Q ₂₄ (), the input signal of the phase shift circuit 24 appearing at the collector of the transistor Q ₂₆ (), it, two signals appearing at the collector of Torajisuta Q ₂₈ (), ( The combined signal of () is combined at the common connection point of the collectors of these three transistors Q ₂₄ , Q ₂₆ , and Q ₂₈ , and is given as a signal () to the crystal oscillator 21 via the transistor Q ₂₉ and pin 27.

Here, the transistors Q ₂₅ , Q ₂₆ , and
A constant voltage (Va) is applied to the base of Q ₂₈ , and a voltage (V) for phase control is applied to the bases of the transistors Q ₂₄ and Q _27.
b) is applied. This causes the transistor Q ₂₆ ,
The amplitude level of the input / output signals (), () of the phase shift circuit 24 appearing at the collector of Q ₂₄ is controlled by the voltage (Vb). As a result, the phase of the signal () is controlled by the voltage (Vb), and the signal () having the phase required by the voltage (Vb) is obtained.

Here, the phase shift circuit 24 will be described. The phase shift circuit 24 is composed of a series circuit of two resistors R ₁₁ and R ₁₁ and a capacitor C ₁₁ . The resistor R ₁₁ is inserted between the input / output terminals 241 and 242 of the phase shift circuit 24,
The resistor R ₁₂ and the capacitor C ₁₁ are inserted between the output terminal 242 and the reference potential point (ground (GND) in the figure).

Now, assuming that the input signal () is a sine wave signal of frequency (), the transfer function T of the phase shift circuit 24 is T = (+ jωτ) / {1 + jω (1 + γ) τ} ...
It is given in (1). However, ω = 2π, γ = R ₁₁ /
R ₁₂ and τ = C ₁₁ R ₁₂ . At this time, the delay amount φ ₅ of the phase shift circuit 24 is φ ₅ = tan ⁻¹ [−ωγτ / {1 + ω ² (1 + γ)
τ ² }] ... (2). Signals (), (), resistance R ₁₂ , capacitor C
The phase relationship of the signal () at the ₁₁ connection points is as shown in the vector diagram of FIG. Where φ ₄ is the signal
The phase difference between () and the signal () is shown.

Generally, the variation of resistance is ± 20 when manufacturing IC.
%, But the resistance ratio is highly accurate and can be suppressed within ± 3%. Similarly, variations occur in capacitors, but the ratio can improve accuracy. Thus, in the formula (2), gamma allogeneic impedance elements, i.e. resistors _{R 11,} since the impedance ratio of _{R 12,} hardly change even if the fluctuation characteristics of these resistors _{R 11, R 12,} can be regarded as constant. For example, in the IC, even if the resistance values of the resistors R ₁₁ and R ₁₂ move within a range of ± 10 to 20%, the fluctuation of γ can be suppressed within ± 3%.
On the other hand, τ is the impedance ratio of different impedance elements. Therefore, it is a variable showing a variation of about ± 40% in IC. However, it is assumed that the change of the delay amount φ ₅ due to the change of the frequency () can be ignored.

The relationship between τ and φ ₅ is shown in FIG. As is clear from FIG. 3, φ ₅ is an inflection point (ωτa, φ
₅ a) and before and after this inflection point the rate of change of φ ₅ is very small. Therefore, once the desired delay amount is determined,
This is the inflection point (ωτa, φ of the phase function shown in FIG.
_The circuit 24 may be designed so as to come close to 5a). This circuit design may be performed so as to substantially satisfy the condition that the value obtained by differentiating the delay amount φ ₅ by the variable τ becomes zero.

Differentiating φ ₅ by τ, Then, the condition that this becomes zero is ω ² τ ² (1 + γ) = 1 (4). By designing the circuit so as to satisfy this condition, the variation amount Y of the delay amount φ ₅ with respect to the variation amount X of (ωτ) can be suppressed to several percent.

As described above, according to this embodiment, even if the element characteristics change, the delay amount of the phase shift circuit 24 does not change, and the input / output signals (),
(Is always a constant amplitude in the amplitude limiting circuit 25, so
It is possible to suppress fluctuations in the VCO frequency variable range due to fluctuations in element characteristics.

In the present invention, the resistors R ₁₁ and R ₁₂ may be replaced with capacitors, and the capacitor C ₁₁ may be replaced with resistors. In addition, it goes without saying that an inductive impedance element may be used as the reactance impedance element.

〔The invention's effect〕

As described above, according to the present invention, even if the element characteristics change,
It is possible to provide a VCO suitable for IC without changing the predetermined variable frequency range.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the structure of an embodiment of the present invention, and FIG.
FIG. 4 is a vector diagram for explaining the operation of the phase shift circuit of FIG. 1, FIG. 3 is the same phase characteristic diagram, FIG. 4 is a circuit diagram showing a VCO provided in the APC circuit, and FIG. 5 is FIG. 6 is a vector diagram for explaining the operation of FIG. 21 ... Crystal oscillator, 24 ... Phase shift circuit, 25 ...
... Amplitude limiting circuit, 26 ... Combining circuit.

Claims (1)

[Claims] 1. An input terminal to which an input signal having a predetermined frequency is supplied, a first impedance element having one end connected to the input terminal and exhibiting either resistance or reactance, and the first impedance element. A series circuit of a resistive impedance element and a reactance impedance element connected between the other end of the impedance element and a reference potential point is included, and the input signal is applied to a connection point of the first impedance element and the series circuit. A phase shift circuit that obtains a second signal that is phase-shifted by a predetermined amount of phase, and a differential amplifier circuit. The input signal and the second signal are supplied, and the amplitudes of these signals are limited and output. An amplitude limiter circuit, and the input signal and the second signal whose amplitude is limited by the amplitude limiter circuit are appropriately used according to a voltage for phase control. A resistive impedance that forms the series circuit of the phase shift circuit, and a synthetic circuit that outputs the synthetic signal to the output terminal and a resonator that is inserted between the output terminal and the input terminal. A voltage controlled oscillator circuit, wherein the constant of each impedance element is set to a value such that the variation of the phase shift amount becomes smaller than the variation of the impedance ratio of the element and the reactance impedance element.