JPS59221009A - Variable frequency oscillating circuit - Google Patents

Abstract

PURPOSE:To increase the variable frequency range together with improvement of stability for a variable frequency oscillating circuit and at the same time to convert this circuit suitably into an IC, by making use of the exponential function characteristics of a transistor (TR) to correct the control current to obtain the linear control signal/oscillation frequency characterisitcs. CONSTITUTION:A current I13 flows to a resistance R11 from an amplifier 13, and as a result the collector current I16 of a TRQ16 is equal to that obtained by multiplying the saturation current Is of the TRQ16 by the exponential function of the difference between the base-emitter voltage a TRQ17 and (I13XR11). As a TRQ19 and a TRQ15 constitute a current mirror circuit 14, the collector current I5 of a TRQ5 is equal to I16. Therefore I5(0) is equal to the value obtained by multiplying the current Is by the exponential function of the base voltage of the TRQ17 when the current I5 is equal to I5(0) when I13=0 is satisfied. As a result, I5(0)/I5 is obtained as the exponential function of I13. Then the current I5 changed in terms of an exponential function from the standard I5(0) to I13. Therefore the oscillation frequency has a linear change to the current I13.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a variable frequency oscillation circuit with good linearity.

Background technology and its problems A variable frequency oscillation circuit whose oscillation frequency can be controlled by voltage or current is called ■CO or CCO, but this ■CO or CCO is divided into LC oscillation type and multi-vibration type. It can be broadly classified.

In general, the LC oscillation type uses a variable capacitance diode in the resonant circuit and supplies a control voltage to it to vary the oscillation frequency, while the multi-vibration type uses a variable capacitance diode to control the charging and discharging current of the capacitor, and a threshold The oscillation frequency is varied by controlling the drive level.

However, in the LC oscillation type, if a super-step junction variable capacitance diode is used, it is not suitable for IC implementation, and if a general PN junction variable capacitance diode is used, the variable capacitance range is small, so the variable frequency range is narrow. Put it away.

In addition, the multi-pie break type can only realize CO or CCO, which has poor oscillation stability and poor C/N, and cannot hope for performance equal to or better than the LC oscillation type.

Therefore, a CCO shown in FIG. 1 is being considered as a CCO that eliminates these problems.

That is, in FIG. 1, the collector of a transistor Q1 is connected to a power supply terminal T1, a constant current source Q2 is connected between its emitter and ground, and a resistor R1 and a solid-state resonator are connected between its collector and base. X1 is connected in parallel, and a capacitor C1 is connected between its base and emitter.
is connected, and the output terminal T2 is connected to this emitter.

Also, transistor Q3. The emitters of Q4 are connected to each other, and a variable constant current source Q5 is connected between the emitters and ground, thereby forming a differential amplifier (1). Furthermore, transistor Q4. Q? have their emitters connected to terminal T1, their bases connected to each other, and
A current mirror circuit (2) is configured which is connected to the collector of the transistor Q6, has the transistor Q6 as an input terminal, and has the terminal T1 as a reference potential point. And transistor Q3. The collector of Q4 is a transistor Qe.

Inverting amplifier (3) each connected to the collector of Q7
is configured.

Furthermore, a feedback capacitor C2 is connected between the collector and base of the transistor Q4, and the transistor Q4
The base of the transistor Q3 is connected to the bias power supply V1 through the resistor R2, and the base of the transistor Q3 is also connected to the power supply V1. Further, the collector of transistor Q4 is connected to the emitter of transistor Q1.

According to such a configuration, the circuit (11, (2) connects the base of the transistor Q4 to the inverting input terminal, and connects the base of the transistor Q4 to the inverting input terminal.
．． Since it works as an inverting amplifier (3) with the collector of Q7 as the output terminal, the AC equivalent circuit of the circuit in Figure 1 is
The result will be as shown in the figure. That is, negative feedback is applied to the amplifier (3) by the capacitor C2, the input terminal of the amplifier (3) is shunted by the resistor R2, and the amplifier (3) is shunted by the resistor R2.
3) is connected to the emitter of transistor Q1.

Therefore, the output admittance Y of the amplifier (3) at this time is: (1) ω: Angular frequency I5: Constant current of current source Q5, which is equivalent to a series circuit of a resistor and a capacitor.
The Q of the capacitance is expressed as Q-1/ωC2R2.

Therefore, if Q>>1, the admittance Y can be regarded as only a capacitance, and its equivalent capacitance C is as follows. That is, when looking at the amplifier (3) side from the emitter of the transistor Q1, this can be regarded as the capacitance Cx.

Therefore, the circuit of FIG. 2 can be further illustrated isometrically as shown in FIG. The circuit shown in FIG. 3 is a Colpitts oscillation circuit, which oscillates at the series resonance frequency of the inductance and capacitance gl C1, Cx of the vibrator X1.

At this time, the equivalent capacitance Cx is expressed by equation (ii), which changes depending on the magnitude of the current 15. Therefore, the circuit shown in FIG. 1 is a Colpitts oscillation circuit, and its oscillation frequency can be varied by the constant current IS of the variable constant current source Q5.

In this way, CCO can be realized, but in this case, especially the first
According to the CCO shown in the figure, an element such as a hyperstep junction variable capacitance diode is not required, so it can be easily integrated into an IC. In addition, the equivalent capacitance Cx is expressed by equation (ii), and the current I5
Since the capacitance Cχ can be varied over a wide range, the variable frequency can be widened.

Furthermore, since this CCO is basically LC oscillation, it has high stability and a good C/N. Also, the number of parts is small.

Also, the emitter of transistor Q1 and the transistor Q
4. ．． No direct current flows between the collector of Q7 and
Since the potentials at these points are determined by transistor Q+, power supply voltage Vcc can be lowered. moreover,
Since the output terminal of amplifier (3) is connected to transistor Q1, compared to the case where the input terminal is connected, transistor Q
The oscillation signal level at one emitter can be increased.

As described above, the CCO of FIG. 1 has many advantages. However, in this CCOo, the equivalent capacitance Cx is expressed by equation (ii) for the control current I5, and the capacitance Cx is
5, the oscillation frequency f with respect to the current I5 changes non-linearly as shown by the solid line in FIG. For this reason, the control sensitivity to the oscillation frequency f is high in the narrow range of the oscillation frequency f (upper side of Figure 4), and the control sensitivity is low in the low range of the oscillation frequency f (lower side of Figure 4), making it difficult to use. There are drawbacks. Also,
If this CCO is used in a PLL, the loop gain will change significantly depending on the oscillation frequency f, so there is a drawback that a PLL with desired characteristics cannot be obtained.

OBJECT OF THE INVENTION The present invention attempts to eliminate these problems.

SUMMARY OF THE INVENTION Therefore, in the present invention, the control current I5 is corrected using the exponential characteristic of the transistor to make the control signal versus oscillation frequency characteristic linear.

In the embodiment, that is, in FIG. 5, the collector and emitter of a transistor Q6 are connected as a constant current source Q5.

Also, transistor Q11. The emitters of Qj2 are connected to each other, and a constant current source Q13 is connected between the emitters and ground, and the bases of transistors Q and Qj2 are connected to control terminals Ttt and T12, and a differential amplifier (11) is connected. is configured. Furthermore, transistor Q1
4. Qj6 makes terminal T1 a reference potential point, and
A current mirror circuit (12) with the transistor Q14 as the input side is configured, and the transistor Q14
, the collector of Q15 is the transistor Q11゜Qj
, 2 are connected to the collectors of the non-inverting amplifiers (1
3) is constructed.

And transistor Q12. The collector of CLts is connected to the base of transistor Q16, the emitter of transistor Q16 is connected to terminal T1, and a diode-connected transistor Q1r and resistor R11 are connected between terminal T1 and the base of transistor Qts.
are connected in series, and a constant current source Qie is connected between the midpoint between the transistors Q, 17 and the resistor R11 and the ground.

Further, the collector of transistor Q1G is connected to the collector of transistor Q19, and transistor Qt is connected to transistor Qzs and transistor Q6.
A current mirror circuit (14) is configured with s as an input side and ground as a reference potential point.

Note that a control voltage E is supplied between the terminals T11 and T12.

In such a configuration, from the amplifier (13) to the resistor R
If the current flowing towards 11 is shifted from 113, the terminal T
The control voltage E supplied to the terminal Tx
When the polarity of 1 is positive, I 13 > 0, and when the polarity of the terminal T12 is positive, 11a < 0, and this current I 1g corresponds to the control voltage E, and E
If =0, then 11a=0.

And for iai transistor 01G, Qj4
If we ignore the base current of Vsi+it I t3Rxt=VBix6V[]ε
xG, Veizv: Transistor QIB, Q
Since it is the base-emitter voltage of j7, if the collector current of transistor Q16 is 11G, Ix6=Is (exp((Vag17113R11
))) T IS: Becomes the saturated main current of transistor 016.

Also, the collector current Its of transistor QIG is the same as that of transistor Q1. Since the transistors Q1s and QB constitute a current mirror circuit (14), 5-Ic6':; I s (exp ((VBi+tt I
13R11)) jT...(iii).

Therefore, if the collector current I5 when 113 = 0 (E-0) is 15 (0), then 15 (o) = I s (exp (VB617)
)T...(iv) Therefore, from equation (iii) and (iv), '1 = esp (I x3Ru) T. That is, the current I5 changes exponentially with respect to the current 113 from the reference current 16 (0).

Therefore, the oscillation frequency f changes almost linearly with respect to the current 113, as shown by the broken line in FIG.

Note that when I3=0 (E=0), the collector current Iz6 of the 1-transistor Q1s is the same as the transistor Q1.
This is equal to the constant current 118 of the constant current source Q+8, so 15=Ize, and the oscillation frequency f is the reference frequency fo.

Thus, according to the present invention, the oscillation frequency f can be varied linearly with respect to the control voltage E or the control current Ii3. Furthermore, since this linearity correction is performed using the rank function characteristics of the transistor, there is little variation or fluctuation in the control signal versus oscillation frequency characteristics.

Therefore, constant control sensitivity can be obtained regardless of the oscillation frequency f. Further, in PLL, the loop gain is constant, and desired characteristics can be easily obtained.

In the example shown in FIG. 6, the emitter of the transistor Q1 is grounded, and in the current mirror circuit, content may be added in parallel or in series with the capacitor Cx as necessary.

Effects of the Invention The oscillation frequency can be changed linearly with respect to the control signal. Moreover, it is suitable for IC implementation, and has excellent stability and C/C/
N is also good, and the variable frequency range is wide. Also,
It can also operate at low voltages and has a small number of components.

[Brief explanation of the drawing]

Figures 1 to 4 Figure 1 is a diagram for explaining this invention, Figure 5
6 and 6 are connection diagrams of an example of the present invention. (3) is an inverting amplifier. Procedural amendment November 22, 1981 1, Indication of the case Patent Application No. 95354 of 1988 2, a 'J'l (') Name 4rF variable frequency oscillation circuit 3, Person making the amendment Relationship to the case Patent Applicant Address: 6-7-35, Kitashina-yo, Tokyo Parts-Yo-ku Name (21
8) Norio Ohga, Representative Director of Sony Corporation 6. Number of inventions to be increased by amendment (1) Formula (i) on page 5, line 4 of the specification is corrected as follows. ... (i)'' (2) Correct the formula (ii) on page 6, line 1 as follows. (3) Correct the formula on page 12, line 2, as follows. (4) In the drawings, Figure 6 will be corrected as shown in the attached sheet. that's all

Claims (1)

[Claims] A differential amplifier and a current mirror circuit are connected to form an inverting amplifier, a feedback capacitor is connected between the output end of the inverting amplifier and the inverting input end, and the inverting input end is shunted by a resistor. The output end is connected to the resonant circuit of the oscillation circuit as its resonant capacitor, and the emitters of the first and second transistors are connected to the base vJf! , another resistor is connected between the bases of the first and second transistors, and the base and collector of the first transistor are connected to each other and to a constant current source. , a collector current of the second transistor is supplied to the differential amplifier as a constant current of its constant current source, and a control current is supplied to a connection point between the base of the second transistor and the another resistor. The oscillation frequency is riJ
Variable frequency oscillator circuit.