KR890004648B1 - Voltage control oscillator - Google Patents

Abstract

A voltage-controlled oscillator of the emittercoupled astable multivibrator type comprises: a first transistor; a second transistor; a series circuit connected between the emitters of the first and second transistors and including at least a capacitor and an impedance element which exhibits an imaginary part for an operating frequency range of the voltage-controlled oscillator being negligible with respect to a real part; first and second loads connected respectively to the collectors of the first and second transistors; feedback means connected between the collector of the first transistor and the base of the second transistor.

Description

Voltage controlled oscillator

1 is a circuit diagram showing a conventional voltage controlled oscillator using an emitter coupled unstable multivibrator.

2 is a signal waveform diagram for explaining an abnormal waveform of each part of the circuit of FIG.

3 is a signal waveform diagram for explaining an actual waveform of each first part.

4 is a characteristic diagram showing an oscillation frequency with respect to a control voltage in the circuit shown in FIG.

Fig. 5 is a circuit diagram showing one embodiment of the voltage controlled oscillation circuit according to the present invention.

FIG. 6 is a signal waveform diagram showing the voltages at both ends of the capacitor for emitter coupling in comparison with the circuit of FIG. 1 and the circuit of FIG. 2. FIG.

FIG. 7 is a circuit diagram showing a relationship of oscillation frequency to control voltage in the circuit of FIG.

8 is a circuit diagram showing another embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

C: condenser V ₁ , V ₂ : voltage source

I ₁ , I ₂ : current source R ₁ , R ₂ , R ₃ , R ₄ : resistance

Q ₁ to Q ₉ : transistor

The present invention relates to a voltage controlled oscillator using an emitter coupled unstable multivibrator.

BACKGROUND OF THE INVENTION In general, a voltage controlled oscillator is frequently used in an electronic device that converts a change in voltage into a change in frequency and processes it, for example, an FM modulator, a PLL circuit, and a voltage / frequency converter.

1 shows a voltage controlled oscillator using a conventional emitter coupled unstable multivibrator. Hereinafter, the configuration and operation of the oscillator will be described, and the problem will be described.

In FIG. 1, transistors Q ₁ -Q ₇ , resistors R ₁ , R ₂ voltage source V ₁ , current sources I ₁ , I _2, and capacitor C constitute an emitter coupled unstable multivibrator, and transistors Q ₈ , Q ₉ And resistors R ₃ and R ₄ are configured to convert the control voltage V ₁ from voltage source V ₂ into a current to produce an operating current of the multivibrator.

2 shows the waveforms of the parts A, B, C and D during operation and the states of the transistors Q ₁ , Q ₃ , Q ₆ and Q _{7 which} operate in switching (high level) and off (low level). . In the period T ₁ , the transistors Q ₃ and Q ₇ are turned on, and the transistors Q ₁ and Q ₇ are turned off by the positive feedback loop. At this time, as the current of the capacitor C is the emitter of the transistor Q ₇ → capacitor C → the collector of the transistor Q _8, a current determined by the collector current of the transistor Q ₈ flows through the capacitor C. In this state, since the transistor Q ₇ is turned on, its emitter potential is fixed. As the charge of the capacitor C proceeds, the emitter potential of the transistor Q ₆ decreases, and eventually the transistor Q ₆ is turned on. Immediately after the transistor Q ₆ is turned on, the transistor Q _{1 is} also turned on, and the transistors Q ₃ and Q ₇ are turned off by the positive feedback loop, thereby bringing the state of the period T ₂ . In this way, the oscillation is maintained by repeating the states of the periods T ₁ and T ₂ .

Here, the ideal oscillation frequency F ₁ of this circuit is obtained. The base potentials V _{B6 (2)} and V _{B7 (1)} of the transistors Q ₆ and Q ₇ in the state of the period T ₂ are

V _{B6 (2)} = V _CC -V _BE2 -V _BE5 . … … … … … … … … … … … … … … … … … (One)

V _{B7 (2)} = V _CC -V _r ¹ _f -V _BE1 V _BE1 ... … … … … … … … … … … … … … … … (2)

Single V _CC : Voltage of Power (+ B)

V _ref : Voltage of voltage source V ₁

V _BEn is the base of transistor Q _n (n = 1-9). The forward drop voltage between the emitters is also the same.

At this time, since the transistor Q ₆ is turned on, the emitter potential V _{E6 (2)} of the transistor Q ₆ is represented by Equation (1).

V _{E6 (2)} = V _CC -V _BE2 -V _BE5 -V _BE6 . … … … … … … … … … … … … … … … (3)

Is fixed. On the other hand, since the transistor Q ₇ is turned off, the emitter potential V _{E7 (2)} of the transistor Q _{7 drops} simultaneously with the charging of the capacitor C. Therefore, the forward drop voltage between the base and the emitter of the emitter potential V _{E7 (2) E} of the transistor Q ₇ at the end of the period T _{2 is} higher than the base potential V _{B7 (2)} of the transistor Q ₇ shown in Equation (2). When it's as low as V _BE7

V _{E7 (2)} = V _CC -V _ref -V _BE1 -V _BE4 -V _BE7 . … … … … … … … … … … … … (4)

At the moment, the circuit state is reversed and the state becomes the period T ₁ .

At this time, the emitter ground of the transistor Q ₇ above V _{BE7 (1)} is above the emitter grounds V _{BE7 (1)} of the transistor Q ₇ is instantaneously because the transistor Q ₇ is switched from an off state to an on state,

V _{BE7 (1)} = V _CC -V _BE2 -V _BE4 -V _BE7 ... … … … … … … … … … … … … … … … (5)

Is changed. The emitter potential of transistor Q ₇ changes instantaneously from to V _{E7 (2)} and the potential difference is given by equations (4) and (5)

V _{E7 (1)} -V _{E7 (2) E} = V _ref . … … … … … … … … … … … … … … … … … … … … (6)

Becomes However, the forward drop voltage V _BE7 between all transistor bases and emitters is assumed to be the same. This potential difference V _ref is transmitted as it is to the emitter of the transistor Q _{6 which} is the other end of the capacitor C, and the emitter potential V _{E6 (1) S} of the transistor Q ₆ at the beginning of the period T ₁ is expressed by Equation (3),

V _{E (1)} = V _mm -V _BES = V _mm -V _BE -V _BE5 -V _BE6 + V _ref . … … … … … … (7)

Becomes In this state, the capacitor C starts charging in the opposite direction in the case of the previous period T ₂ , and the emitter potential of the transistor Q ₆ starts to drop.

V _{E6 (1) E} = V _CC -V _ref -V _BE3 -V _BE5 -V _BE6 . … … … … … … … … … … … (8)

At the next step, the circuit state becomes a period T2 again in the period T1.

On the other hand, between the period T _1, so the emitter voltage V _{BE7 (1)} of the transistor Q ₇ is turned on and the transistor Q ₇ is _{V E7 (1) = V CC} - V BE2 - V BE - V BE7 ... … … … … … … … … … … (9)

As constant.

Thus, variation in the potential difference △ V _C at both ends of one period of the capacitor C has the formula (7), (8)

Δ = V _{E6 (1) S} -V _{E6 (1) I} = 2 VR _ref ... … … … … … … … … … … … … … … … … 10

Becomes However, the forward drop voltage V _BEn between the base and emitter of all transistors is to be the same.

In addition the current flowing through the capacitor C is determined by the collector current of a period T ₁ the transistor Q _8, the period T ₂ is determined by the collector current of the transient substation emitter Q _9. Here, when the transistors Q ₈ and Q ₉ are transistors of the same characteristics and the resistances of the resistors R ₃ and R ₄ are the same, the collector currents of the transistors Q ₈ and Q _{9 become} the same. If the current ic to the current ic as a first assist is configured such that its value is controlled by a control voltage V _1. The time t of the periods T ₁ and T ₂ shown in FIG.

…………………………………… (11)

… … … … … … … … … … … … … … (11)

However, C _a : becomes the capacitance of the capacitor C. Therefore, the ideal oscillation frequency Fi has a period of 2t,

…………………………………………… (12)

… … … … … … … … … … … … … … … … … (12)

Becomes In other words it is possible to linearly control the oscillation frequency Fi with respect to the current ic ic By the current controlled by a control voltage V _1. However, in an actual circuit, a delay occurs in operation due to the parasitic capacitance of the element or the floating capacitance of the wiring. This delay occurs at the inversion of the periods T ₁ and T ₂ , and as shown in FIG. 3, the waveforms of the parts A, B, C, and D, and the rising and falling of ΔV ₀ , respectively, are used for Td ₁ and Td ₂ . There will be a delay. Considering these delay times Td ₁ and Td ₂ , the actual oscillation frequency F _r is

…………… (13)

… … … … … (13)

Becomes As shown in equation (13), the actual oscillation frequency F _r can also be controlled by the current ic, but the linearity of the oscillation frequency F _r with respect to the current ic is lost due to the term (Td ₁ + Td ₂ ). In addition, since (Td ₁ + Td ₂ ) is always constant, as the oscillation frequency F _r is controlled to be large (time t becomes small), there is a drawback that the nonlinearity becomes larger. 4 shows the relationship of the oscillation frequency to the control voltage V ₁ of such a circuit. In the figure, it can be seen that as the oscillation frequency increases, the nonlinearity increases.

An object of the present invention is to provide a voltage controlled oscillator capable of improving linearity of an oscillation frequency with respect to a control voltage.

According to the present invention, a first transistor and a second transistor are connected between emitters of the first and second transistors, and each of at least one capacitor and an impedance element (the impedance element is an operating frequency range of a voltage controlled oscillator). In which the imaginary part represents a negligible value for the real part, and a first and a second load connected to the collectors of the first and second transistors, respectively. Feed-back means connected between the collector of the transistor of the transistor and the base of the second transistor and between the collector of the first transistor and the base of the first transistor: connected to emitters of the first and second transistors, respectively Emitter coupled unstable multivibrator type voltage control comprising: first and second current sources and a control voltage source commonly connected to said first and second current sources An oscillator is provided.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 5 is a circuit diagram of one embodiment. In FIG. 5, the difference from the first first embodiment is that the resistor R is connected in series with the capacitor C. In FIG. In other words, a series circuit between the resistor R and the capacitor C is inserted between the emitters of the transistors Q ₆ and Q ₇ . Since all other configurations are the same as those of the first drawing, detailed description thereof will be omitted here.

The operation in the above configuration will be described. Since the charging current ic of the capacitor C flows through the resistor R, the potential difference ΔV _R at both ends is always

ΔV _R = i.R _a . … … … … … … … … … … … … … … … … … … … … … … … … … (15)

R _a is the resistance of the resistor R. Since the potential difference ΔV _c of the capacitor C when there is no resistance R is 2 _ref in Equation (10), the potential difference Δ _{c (R)} of the capacitor C in FIG. 5 is

Δc _(R) 2V _ref -icRa

Becomes Therefore, when the delay times Td ₁ and Td _{2 of the device} are considered, the oscillation frequency F _r (a) is the same as in Equation (13) above.

Becomes From here

………………………………………………………… (17)

… … … … … … … … … … … … … … … … … … … … … … (17)

If the resistance value Ra of the resistor R is selected so that Eq.

…………………………………………………… (18)

… … … … … … … … … … … … … … … … … … … … (18)

Is the same as the ideal case shown in equation (12), and the oscillation frequency F _r (R) changes linearly with the current ic.

If this is expressed as the voltage across the capacitor C, it is equal to the sixth degree.

6 shows the case of R = 0 (conventional case) and the case of Ra = (Td ₁ + Td ₂ ) / 2C _a (in case of the present embodiment). In the latter case, the period becomes 2t for any value of the current ic, which is the same as the ideal case. In FIG. 6, the time t 'is

………………………………………………………… (19)

… … … … … … … … … … … … … … … … … … … … … … (19)

Is indicated as.

7 shows the relationship of the oscillation frequency F _r to the control voltage V ₁ using the resistance value Ra as a parameter. In the figure, it can be seen that when Ra = (Td ₁ + Td ₂ ) / 2, the characteristic curve shows linearity, and in other cases, nonlinearity is indicated. The resistor used here may be any one that operates as a resistor with respect to the oscillation frequency F _r . In other words, it is possible to use an impedance element (including an IC circuit) in an operating frequency range in which the imagery farat is negligible with the real farat.

8 is a circuit diagram showing another embodiment of the present invention. In this embodiment, the resistor R is divided into two resistors R _A and R _B , and these resistors R _A and R _B are connected in series to one end and the other end of the capacitor C, respectively. Also in such a structure, there exists the same effect as the previous embodiment.

로 하면 좋다. 외부부착핀 P₁, P₂를 설치하면 이들 핀 P₁, P₂가 전원의 단자에 접속되는 경우가 있으나, 이 저항 R₁, R₂가 트랜지스터 Q₆, Q₇의 에미터에 접속되어 있으면 충분한 프로텍트 효과를 기대할 수 있다.In addition, this as another advantage of such configuration is the circuit either when mounting the capacitor C to the outside as a semiconductor integrated circuit of the terminals for external connection of the capacitor C pins P _1, P ₂ is palyo, resistors R _1, R _{v It} can be used as a protection resistor for preventing excessive current of transistors Q ₆ and Q ₇ connected to the terminals P ₁ and P ₂ , respectively. In order to obtain this effect transistors Q _6, Q ₇ with respect to the effective resistance R _1, the resistance value of R ₂

It is good to do. External pin P _1, by installing the P ₂ these pins P _1, P ₂ a, but the case which is connected to the power supply terminal, a resistor R _1, R ₂ and the transistor Q _6, if it is connected to the emitter of Q ₇ Sufficient protection effect can be expected.

As described above, according to the present invention, in a voltage controlled oscillator using an emitter coupled type unstable multivibrator, the linearity of the oscillation frequency with respect to the control voltage is extremely good by adding a resistor in series to the capacitor for emitter coupling. A voltage controlled oscillator suitable for integrated circuits can be provided.

Claims (5)

At least one capacitor and an impedance element connected between the first transistor, the second transistor, and the emitters of the first and second transistors, the imaginary part being a real number in the operating frequency range of the voltage controlled oscillator. (A) negligible with respect to the negative), a series circuit comprising: first and second loads connected to the collectors of the first and second transistors, respectively: the collector and the second of the first transistor A feedback means connected between the bases of the transistors and between the collectors of the second transistors and the bases of the first transistors; first and second current sources connected to emitters of the first and second transistors, respectively; And: an emitter coupled unstable multivibrator type voltage controlled oscillator comprising: a control voltage source commonly connected to the first and second current sources. 2. The voltage controlled oscillator according to claim 1, wherein said impedance element is one resistor. 3. The voltage controlled oscillator of claim 2, wherein a value of the resistance is approximately equal to a sum of a delay time included in one cycle of the oscillating output of the voltage controlled oscillator divided by twice the capacitance value of the capacitor. 2. The voltage controlled oscillator of claim 1, wherein the impedance element is two resistors having approximately the same value. 5. The device of claim 4, wherein the two resistors have one end connected to the emitters of the first and second transistors and the other end connected to a pair of external attachment pins: the capacitor is between the pair of external attachment pins. Voltage controlled oscillator, characterized in that configured to be connected to.

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