JPS6182506A - Voltage controlled oscillating circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a voltage controlled oscillation 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 synchronization circuit. This APC circuit requires a highly accurate voltage controlled oscillation circuit (hereinafter referred to as vCO). FIG. 4 shows a circuit diagram of the vCO, and FIG. 5 shows its vector relationship diagram.

In FIGS. 4 and 5, the signal outputted from the resonator 11 is phase-shifted by φ in the phase shift circuit 12 to become a signal (6). This signal (6) and the signal (phantom) are synthesized by the synthesis circuit 13 and become the signal (6). This signal (a)
is applied to the resonator 11 via the amplifier circuit 14, and the resonator 11 performs an oscillation operation by delaying the phase by φ.

In FIG. 4, numeral 15 is an APC detection circuit that detects the burst signal (Bu) and the signal (phantom phase difference) and obtains a voltage signal for controlling the synthesis ratio of the synthesis circuit 13.

[Problems with background technology]

In the vCO having such a configuration, variations in the amount of phase shift of the phase shift circuit 12 lead to variations in the frequency variable range.

Therefore, in order to obtain a stable nine-frequency variable range, a highly accurate phase shift circuit is required.

The phase shift characteristics of a phase shift circuit are largely influenced by variations in the characteristics of the elements that make up the circuit.

The characteristics of elements in integrated circuits (hereinafter referred to as ICs) are much less precise than those of individual components.

Therefore, conventionally, when converting into a vCOt-IC, the phase shift circuit 12 has been included as an external circuit.

However, this has problems such as an increase in the number of IC pins, and considering manufacturing costs, it is difficult to completely
O was requested.

[Purpose of the invention]

This invention was made to deal with the above circumstances,
It is an object of the present invention to provide a CO-6 device that does not change a predetermined frequency variable range even if element characteristics change and is suitable for IC implementation.

[Summary of the invention]

This invention sets up a phase shift circuit in which the output phase is expressed by a function whose variable is the impedance ratio of a resistive impedance element and a reactive impedance element, and sets a condition under which the value obtained by differentiating the above function with the above variable becomes zero. The above phase shift circuit is constructed so as to satisfy the following, the input/output signals of this phase shift circuit are amplitude limited using a differential amplifier circuit, and the signals are synthesized as appropriate according to the voltage signal for phase control, and then applied to the resonator. It was designed to be given.

[Embodiments of the invention]

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

In FIG. 1, the signal (5) that has passed through the crystal oscillator 21 is given to the pin 23 of the IC 22, and from this pin 23 it passes through all the transistors 24 to the input terminal 2 of the phase shift circuit 24.
41 is given. The phase shift circuit 24 receives an input signal (i
) is delayed by φ, and the signal (c) is output to the output terminal 242.
f, get. This signal (a) is applied to the bases of the transistors Q17+Q1° of the amplitude limiting circuit 25 via the transistor Qtt. In addition, the input signal (i) of the phase shift circuit 24 is transmitted to the amplitude limiting circuit 2 via the transistor Q□.
5 transistors Q□a+Qts. Transistor Q14 + of this amplitude limiting circuit 25
For the pace of Qss + Qlg + Qlg, a constant voltage source v11 and a second transistor Q are used. , Qlst-.

In the amplitude limiting circuit 25, the transistor Qlf +Q
B constitutes a differential amplifier circuit using Ill as a constant current source. Also, the transistor Qi* r Qz. ■,.

It forms a differential amplifier circuit using as a constant current source. Therefore, the signal (6) output from the phase shift circuit 24 is output as a constant amplitude signal to the collectors of the transistors Q1A to Q8 DEG due to the amplitude limiting action of the differential amplifier circuit. Tsut! ri) Langister Ql? ~Q. The amplitude level of the signal appearing at the collector of the constant current source If! l 114
It is proportional to the amount of current and does not depend on the amplitude level of the phase shift circuit 24. This is the same for the signal (i) which is the other input of the amplitude limiting circuit 24, and the differential amplifier circuit of the transistor Qss p Q14 with 11□ as a constant current source and the transistor Qts with 112 as a constant current source. ,
Due to the amplitude limiting action of the differential amplifier circuit Q, the signal (phantom) is outputted from the collectors of the transistors Q□, ~Q1° as a signal with a constant amplitude.

The output signal (a) of the phase circuit 24 subjected to the amplitude limiting action is transmitted to the transistor Q1. The collector of the transistor Q of the synthesis circuit 26! 4. Supplied to the emitter of Q□. In addition, the input signal to the phase shift circuit 240 subjected to the amplitude limiting effect is input to the combining circuit 26)5z y7y=Qa, , i r Q
, xq, I). In addition, the phase shift circuit 24
The input/output signals (,) and (mi) are transistor Q13.
゜Ql, are combined at the common connection point of the collectors of transistors Q3. is supplied to the emitter of Transistor (l
The output signal (mi) of the phase shift circuit 24 appearing at the collector of transistor Qss (mi), the input signal (phantom) of the phase shift circuit 240 appearing at the collector of transistor The composite signal is generated by these three transistors Q1..Q□,
Q8. The signal (a) is synthesized at the common connection point of the collectors of
As Transistoro 81. It is applied to the crystal oscillator 21 through the bottle 2.

Here, the transistor Q□ of the synthesis circuit 26.

A constant voltage (Va) is applied to the pace of Q□ and Ql.
Hey, transistor Q! 4 IQ! ? A phase (control voltage (vb) is applied to the base of the transistor Qxm is controlled by the voltage (vb).As a result, the phase of the signal (a) is controlled by the voltage (vb), and a signal (a) with the required phase is obtained by the voltage (vb). become.

Here, the phase shift circuit 241C will be explained. This phase shift circuit 24 consists of a series circuit of two resistors J1+R and a capacitor C1□. The resistor R11 is inserted between the input and output terminals 241 and 242 of the phase shift circuit 24,
Resistance R1! , a capacitor C□1 is inserted between the output terminal 242 and a reference potential point (in the case of the figure, ground (GND)).

Now, assuming that the input signal (a) is a sine wave signal of t-frequency (f), the transfer function T of the phase shift circuit 24 is T=(1
+jωτ)/(1+jω(1+γ)τ) ...(1)
Larel given by. However, 'J=2 "j' * r="
”/R1z *τ”C11RI. At this time, the phase delay amount φ of the phase shift circuit 24 is φ,=tan-'[-ωrτ/(1+ω2(1+r)
τ2)]...(2). Signal (i), (a)
The phase relationship of the signal (6) at the connection point between the resistor atxl and the capacitor 011 is K as shown in the vector diagram in FIG. Here, φ4 indicates the phase difference between signal (a) and signal (6).

In equation (2), r is the impedance ratio of the same type of impedance element, that is, the resistors R1l and Rlm, so
Even if the characteristics of these resistors RIJIR1j change, they hardly change and can be regarded as constants. For example, in an IC, even if the resistance values of resistors R1□ and R12 move within the range of ±10 to 2 (l), the variation in r is suppressed to within ±30%. It is assumed that the change in the phase delay amount φS due to the impedance change can be ignored.

The relationship between τ and φS is shown in FIG. As is clear from Fig. 3, φ5 is an inflection point (ωτa, φsa
), and the rate of change in φS is very small before and after this inflection point. Therefore, the desired phase delay amount is determined, and this is the inflection point of the phase function (ωτa, φam
) The circuit 24t may be designed so that it is close to . This circuit design may be performed in such a way that the phase lag amount φ and the value differentiated by the t-variable τ substantially satisfy the condition that the value is zero.

When differentiated with respect to φ and t−τ, the following is obtained.The condition for this to become zero is ωτ(1+γ)=1 (4). By designing the circuit so as to satisfy this condition, the amount of variation Yi of the amount of lag φ with respect to the amount of variation X of (ωτ) can be suppressed to several percent.

As described above, according to this embodiment, even if the element characteristics change, the phase delay amount of the phase shift circuit 24 does not change, and the input/output signal (i) of the phase shift circuit 24 does not change.
(c) is always set to a constant amplitude by the amplitude limiting circuit 25, so that fluctuations in the frequency variable range of vCO due to fluctuations in element characteristics can be suppressed.

In the present invention, the resistor Rts + Rtz t" capacitor may be substituted, and the capacitor C1l may be replaced with a resistor. Also, it goes without saying that an inductive impedance element may be used as the reactive impedance element.

〔Effect of the invention〕

As described above, according to the present invention, even if the element characteristics change,
Since the predetermined frequency variable range does not vary, it is possible to provide COt- which is suitable for IC implementation.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of an embodiment of the present invention (a circuit diagram shown in FIG.
The figure is a vector diagram for explaining the operation of the phase shift circuit in Figure 1, Figure 3 is a phase characteristic diagram, and Figure 4 is an APC diagram.
A circuit diagram showing the vCO provided in the circuit, and FIG. 5 is a vector diagram for explaining the operation of FIG. 4. 21... Crystal resonator, 24... Phase shift circuit, 2
5... Amplitude limiting circuit, 26... Synthesizing circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 2 Figure 3 Q) ω Figure 4 Figure 5

Claims (1)

[Claims] A resistive impedance element and a reactive impedance element are inserted in series between an input terminal and a reference potential point, and an output terminal is provided in this series circuit,
A phase shift circuit in which the phase of the signal obtained at this output terminal is expressed by a function with the impedance ratio of the resistive impedance element and the reactive impedance element as a variable, and a differential amplifier circuit, and the phase shift circuit is given an input signal and an output signal, and an amplitude limiting circuit that limits the amplitude of these signals; and an input signal and an output signal of the phase shift circuit whose amplitude is limited by this amplitude limiting circuit according to a voltage signal for phase control. It comprises a synthesis circuit that performs synthesis as appropriate, and a resonator inserted between the output terminal of this synthesis circuit and the input terminal of the phase shift circuit, and the phase shift circuit differentiates its output phase with the variable. A voltage controlled oscillation circuit characterized in that it is configured to substantially satisfy a condition that the value becomes zero.