JPS6058714A - Voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To improve the linearity of an oscillation frequency by adding a resistor in series with a capacitor for emitter coupling in a voltage controlled oscillator using an emitter coupling type astable multivibrator. CONSTITUTION:A series circuit comprising a resistor R (resistance Ra) and a capacitor C (capacitance Ca) is inserted between emitters of transistors (TRs) Q6, Q7. Through the constitution above, a potential DELTAVR across the capacitor C is always ic.Ra by a charging current ic. Since a potential difference DELTAVc(R) in this example is 2Vref-ic.Ra. Thus, the oscillating frequency Fr(R) taking delay times taud1, taud2 at the leading and trailing of the element into account is changed linearly as the current ic to any value of the ic by selecting the resistance value Ra so as to obtain the relation of Ra=(taud1+taud2)/2Ca.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a voltage controlled oscillator using an emitter-coupled astable multivibrator.

[Technical background of the invention]

Electronic device 1 For example, FMyR1111! In general, voltage controlled oscillators are often used in circuits, PLL circuits, voltage/frequency converters, and the like.

FIG. 1 shows a voltage controlled oscillator using a conventional emitter-coupled astable multivibrator, and its operation will be explained. Transistors Q1 to Qγ, resistor R17R1, voltage source V1% current source Il, I.

and capacitor C constitute an emitter-coupled astable multivibrator, and transistor Qg.

Q9 and resistors R3 and R4 are controlled voltage v from voltage source 2
It is configured to convert X into a current to generate an operating current for the multivibrator.

Figure 2 shows the waveforms of each part A, B, C, and D during operation and the switching transistors Qt+Qs, Qa, and Q7.
The status is shown as on (high level) or off (low level). In section T, transistor Qa+Q
When y is turned on, transistor Q is turned on by a positive feedback loop.
+ rQ6 is off. At this time, the current path of capacitor C is from the emitter of transistor Q7 to capacitor C.
→ Collector of transistor Q8, transistor Q
A current determined by the collector current of 8 flows through capacitor C. In this state, since the transistor Q7 is on, its emitter potential is fixed, so as the charging of the capacitor C progresses, the emitter potential of the transistor Q6 decreases, and finally the transistor Q6 turns on.

Immediately after transistor Q6 turns on, transistor Q1 also turns on, and a positive feedback loop causes transistors Q11. Q7
is turned off and enters the state of section T3. Thus the interval T,.

T! This state is repeated and oscillation is maintained.

Here, find the ideal oscillation frequency F□ of this circuit. 6- of transistors Qll and Q7 in the state of section T2
7 Potential vB6(2) l R7(1) HaTvB6(2
)=vOO-VBII2-vBII5 °°(1)vB
7(2)=vOO”ref-vnil-vBB4 ・(
2) However, voo: Voltage of power supply element B ■r6f: Voltage source Vs! Pressure"B]Wrt: )Rangemetal Qn (n=1 to 9)
The forward drop voltage between the base and emitter of is (the same applies to the following formula). At this time, since the transistor Q6 is on, the emitter potential vB6C2) of the transistor Q6 is as shown in equation (1), vB6(2) = v00 ``BEl 'B15 - vBE
It is fixed at 6°-(3). On the other hand, since the transistor Qt is off, the emitter potential vI,7 (2) of the transistor Q7 decreases as the capacitor C charges. Therefore, at the end of section T2, 77
Emitter potential of transistor Q7 that goes high vP37 (2)
B is the base potential vB of the transistor Q7 shown in equation (2)
7 (2) When the base-emitter forward drop voltage VBE7 decreases, Tsumashi, "R7 (2
'la="Co"ref "BEl"BF2 "BI
At the moment when B7 becomes ``'('), the circuit state is reversed and becomes the state of section T1.At this time, the emitter potential V□7(1) of transistor Q7 changes from OFF to ON. Because it changes, vFt7(1) instantly
-voo-vBB2-vBB4-vBB7 °°(5)
Changes to The emitter potential of transistor Q7 is vII
I 7 (2) changes instantly from B to vB 7 (1), and the 4-position difference is expressed by the formula (4, (5) to V17 (1) 'E7 (2) W ref ''・(6)
5-. However, it is assumed that the base-emitter forward drop voltage vBBn of all transistors is equal. This potential difference V. , is directly transmitted to the emitter of the transistor Q6 at the other end of the capacitor C, and is the emitter potential V of the transistor Q6 at the beginning of section 1. 6(1)s
According to equation (3), vB6(1) 8 = v00-vBB
2 'B115-VB? , 6 +vref ”' (7
). From this state, the capacitor C is connected to the previous section T2.
Charging starts in the opposite direction to that at the time of , and the emitter potential of transistor Q6 decreases as if v116(1)El=v00 ”ref -VBll!
5'B115-vBI6°°(8), the circuit state changes from section T1 to section T- again.

On the other hand, during the interval TI, the emitter potential of the transistor Q7 is vIll 7 (1) because this transistor Q7 is on.
M? ``' (9) 6- is constant.

Therefore, the amount of change in the potential difference ΔVo between both ends of the capacitor C within one section is given by equations (7) and (8): ΔV=V
-V OR6(1)B R6(1)B=2vref ""'. However, the base-emitter forward drop voltage vBEn of all transistors is assumed to be equal.0 In addition, the current flowing through capacitor C is determined by the collector current of transistor Q8 in section T, and is determined by the collector current of transistor Q9 in section T2. It is determined. Here, assuming that the transistors Qs and Qe have the same characteristics and the resistance values of the resistors R3 and R4 are equal, the collector currents of the transistors Qs and Qs will be equal.

This current is i. Then, as is clear from Figure 1,
Current i. The value of is controlled by control voltage v0. As mentioned above, if the time t of the interval TI+T2 shown in FIG. 2 is included, C&: the capacitance value of the capacitor C. Therefore, since the general period is 2t, the ideal oscillation frequency Fi is as follows. The current i is controlled by the control voltage VI.

By controlling the current i. The oscillation frequency F can be controlled linearly.

[Problems with background technology]

However, in actual circuits, operation delays occur due to parasitic capacitance of elements and stray capacitance of wiring. This delay occurs during the reversal of sections Tl and T2, and as shown in FIG. 3, each section A, B.

The waveforms C and D have delay times of τ and τ6□ of 1 at the rising edge and falling edge of Δvo, respectively. The actual oscillation frequency F, taking into account the delay times τ and τ, 2, is as follows. The actual oscillation frequency F is as shown by the formula α≧
r is also a current i. It can be controlled by the current i. The linearity of the oscillation frequency F with respect to is lost due to the term (τ, 1+τ, 2). Furthermore, since (τ, 1+τd2) is always constant, there is a drawback that the nonlinearity becomes more pronounced as the oscillation frequency F increases (time t decreases). FIG. 4 shows the relationship between the oscillation frequency and the control voltage v0 of such a circuit. From the figure,
It can be seen that the larger the oscillation frequency, the more the nonlinearity appears.

[Purpose of the invention]

The present invention has been made to address the above-mentioned circumstances, and an object of the present invention is to provide a voltage controlled oscillator that can improve the linearity of the oscillation frequency with respect to the control voltage.

9- [Summary of the Invention] This invention is explained using, for example, FIG. It is configured to insert .

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 5 is a circuit diagram of one embodiment. The difference in Figure 5 from Figure 1 is that there is a resistor R in series with the capacitor C.
is connected. That is, a series circuit of resistor R and capacitor C is connected to transistor Q6. It is inserted between the emitters of Q7.

The operation in the above configuration will be explained. The charging current of capacitor C is applied to resistor R. flows, so the potential difference Δ between its ends is
vR is always ΔvR=i, ・Ra...a→ However, R8: the resistance value of the resistor R. The potential difference Δ■o between both ends of the capacitor C when the resistance R is expressed is the formula α1.Since it is 2vr@f, the potential difference Δvc between both ends of the capacitor C in the case of Fig. 5 is
(R) becomes Δvc(R) = 2vref -'c''a.

Therefore, the oscillation frequency Fr(R) when the delay time τ of the element and 1°τ4□ are considered is as follows in the same way as in the previous case. Here, if we choose the resistance value R of the resistor R so that Frequency Fr(R
) varies linearly with the current ieK.

When this is expressed by the voltage across the capacitor C, it becomes as shown in FIG. Figure 6 shows the case of R,=O (conventional case) and R1
-(τ4.0τd2)/2ca (in this example) is shown. In the latter case, the period is 2t for any value of current i0, which is the same as in the ideal case. In addition, in FIG. 6, time t' is expressed as follows.

Figure 7 shows the control voltage v1 with the resistance value R8 set as /4 rammeter.
The relationship between the oscillation frequency F and the oscillation frequency F is shown. From the figure, RIL
= (f, 1+fd2)/2 In case of C, characteristic surface 11j
It can be seen that linearity is shown, and non-linearity is shown in other cases.

FIG. 8 is a circuit diagram showing another embodiment of the invention. In this embodiment, the resistor R is replaced by two resistors RA.

RB, and these resistors RA and RB are connected in series to one end and the other end of a capacitor C, respectively. Even in such a configuration, the same effects as in the previous embodiment can be obtained.

Another advantage of such a configuration is that if this circuit is a flat conductor integrated circuit and a capacitor C is externally attached, terminals 11 and 12 are required to connect the capacitor C, but the resistor RA and RB are connected to terminals 11.
12 can be used for overcurrent prevention. In order to obtain this effect most effectively, the resistance value of the resistor RAIRB should be set to -b.

〔Effect of the invention〕

As described above, according to the present invention, in a voltage controlled oscillator using an emitter-coupled astable multi-by-break, by adding a resistor in series to the emitter-coupling capacitor, the oscillation frequency can be made linear with respect to the control voltage. It is possible to provide a voltage controlled oscillator which has extremely good performance and is suitable for integration into a hand conductor integrated circuit.

13-

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional voltage controlled oscillator using an emitter-coupled astable multivibrator.
A signal waveform diagram to explain the ideal waveform of each part of the circuit shown in the figure,
Fig. 3 is a signal waveform diagram for explaining the actual waveforms of each part of the circuit shown in Fig. 1, Fig. 4 is a characteristic diagram showing the oscillation frequency with respect to the control voltage in the circuit shown in Fig. 1, and Fig. 5 is Circuit diagram showing one embodiment of the voltage controlled oscillation circuit according to the present invention, No. 6
Figure 7 shows a signal waveform diagram comparing the voltage across the emitter coupling capacitor between the circuit in Figure 1 and the circuit in Figure 2.
This figure is a circuit diagram showing the relationship between the oscillation frequency and the control voltage in the circuit of FIG. 5, and FIG. 8 is a circuit diagram showing the main part of another embodiment of the invention. Q1-Q9...transistor, RI 5-R4,R. RA, RB...Resistor, C...Capacitor, 10B.
・・Power supply, V, , V2 ・・Voltage source, Il, I2 ・・
・Current source, 11.12...terminal. 14- Figure 2 Figure 3 Figure 4 Shun Miwaman■ 6th prisoner Figure 7 8FI! J C17 C12R8

Claims (3)

[Claims] (1) First and second transistors with a capacitor connected between their emitters. These first. The first . with a second load. Feedback means inserted between the collector of the first transistor and the base of the second transistor and between the collector of the second transistor and the base of the first transistor. Said 1st. the first . and a second voltage-controlled current source. A resistor is connected in series to the capacitor, and the series circuit is connected to the first . A voltage controlled oscillator characterized in that it is configured to be inserted between the emitters of the second transistor. (2) The resistance value of the resistor is equal to or close to the sum of the delay times included in one cycle of the oscillation output of the voltage controlled oscillator divided by twice the capacitance value of the capacitor. A voltage controlled oscillator according to claim 1, characterized in that: (3) The resistor is the first resistor. The second consists of two resistors,
2. The voltage controlled oscillator according to claim 1, wherein each resistor is connected in series to one end and the other end of the capacitor.