JPH02235413A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To evade a problem such as a delay in an operating speed due to saturation and production of saturation in the capacity and to attain stable oscillation by expanding the dynamic range of both an oscillation circuit section and a variable reactance circuit section so as to obtain a sufficient oscillation output even when the saturation of a transistor(TR) of the oscillating circuit section is suppressed. CONSTITUTION:TRs Q16, Q17 and Q18, Q19 of 1st and 2nd current mirror circuits are connected in series with each collector of a couple of TRs Q11, Q12 of an oscillation circuit 11, and TRs Q20, Q21 of a 3rd current mirror circuit are connected in series with the 1st and 2nd current mirror circuits. An oscillating element 11a is connected between a reference level and a connecting point of the 3rd current mirror circuit and the TRs Q11, Q12 and a feedback circuit is formed between the connecting point and the TRs Q11, Q12. Moreover, a variable reactance circuit section 12 is in capacitor coupling with the connecting pint via a feedback TR Q22 and TRs Q61-Q56 of 4th-6th current mirrors whose outputs are connected in series are connected to one of a couple of outputs of the circuit section 12.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an oscillation circuit that can change the oscillation frequency, and more specifically, to an oscillation circuit that can stably and widely change the oscillation frequency. It is related to.

[Prior Art] In PLLu circuits and the like, an oscillation circuit that is stable and whose oscillation frequency can be varied over a wide range is required.

Conventionally, as this type of oscillation circuit, a configuration as shown in FIG. 2 has been proposed. In the figure, the positive feedback amplifier section 1 is configured to positively feed back a signal obtained at the collector of the transistor Q2 to the base of the transistor Q2 through a capacitor C1.

And transistor Q. Is the frequency specific to the collector? By connecting the oscillation element XZ having the capacitor C
1, the positive feedback is only at a specific frequency, and the output terminal O
An oscillation output having a specific frequency is obtained at the UT. The oscillation element Xz can be represented by an equivalent circuit as shown in FIG. As shown in FIG. 4, when the variable capacitance element Cvll is connected in parallel to the oscillation element XZ, the variable capacitance element Cvll
Depending on the value of (2), the overall impedance (2) mp changes as shown in FIG. In Fig. 5, the frequency loss f, is the parallel resonance frequency when the value of the variable capacitance element C is C,
The frequency r2 is the parallel resonance frequency when the value of the variable capacitance element CvR is C, which is larger than C2, and the frequency f3 is the parallel resonance frequency when the value of the variable capacitance element Cv, I is C, which is larger than Ct. As is clear from Fig. 5, the oscillation element
If the value of the variable capacitor connected in parallel to Z is changed, the parallel resonant frequency will change, so if the value of the variable capacitor is continuously changed, the parallel resonant frequency can also be changed continuously.

By the way, the variable capacitor section 2 connected to one end of the oscillation element XZ can be considered as a variable capacitor.

That is, if the collector voltage of the transistor Q of the variable capacitance section 2 is e0, the input current is 11, and the current flowing through the capacitor C2 is 12, then the current 12 whose phase is shifted by 90'' with respect to the voltage e0 flows through the capacitor C2 and the resistor R. , then the base voltage e of transistor Q,
is, el = R-it - (1)
(However, R is the resistance of the resistor R, {+f!), and the 12 flowing to the capacitor C2 is e(1 iz= 1...(2) R+ jωC (However, C is the capacitance of the capacitor C2, and ω is the angle Frequency).In addition, the input current i+ is: i+ = e.- gm+it ”{3)
(However, gm is mutual conductance), and collector current i3 of transistor Q (=e+ -gm)
is sufficiently larger than the current 12 flowing through capacitor C2, then i. ″.e+l gm’
"{4).The phase of the collector current i3 of the transistor Q is equal to that of the current i! flowing through the capacitor C2. Therefore, the above equations (1), (2) and (4)
, the input current i. is αqr α gm1 ×2= ■ ...{6) 4kT, which means that when viewed from the collector of transistor Q3, there is a resistor with a resistance value of 1 / gm and a capacitance value of R-
It can be regarded as a series circuit consisting of a gm-c capacitor. Also, if gm is large, l/g
m becomes small, and the variable capacitance section 2 in FIG. 2 can be regarded as a capacitor with a capacitance value of R-gm-c. Further, the mutual conductance gm is expressed by the following equation.

Therefore, from the above formula (6), the capacitance value c2 of the variable capacitance section 2 is c.=R-gm-c, and c changes in proportion to I flowing through the current source 1. Therefore, depending on the control signal, By changing the current flowing through the current source 1, obtaining a capacitance proportional to the change in current, and changing the parallel resonance frequency by connecting this capacitance in parallel to the oscillation element XZ, a frequency equal to this parallel resonance frequency can be obtained. oscillation output can be obtained.

Note that if the resistance R+ of the variable capacitance section 2 is created using the junction resistance of the transistor Q, then q/ in the above equation (6)
Since the kT term is eliminated, it is possible to obtain a variable capacitance section 2 that is extremely stable with respect to temperature.

[Problem to be solved by the invention]

In the case of the conventional oscillation circuit described above, as it is clear from the equivalent circuit in Figure 3, it constitutes a parallel resonant circuit, so the impedance is +■ and the oscillation width is in principle infinite, but in reality, the oscillation width is infinite. The upper limit of the amplitude is determined by the saturation potential of the collector of transistor Q4 or Q, and the lower limit is determined by the higher of the saturation potential of the collector of transistor Q or Q3, and the biases E,, E. It differs depending on the size of the Specifically, the upper limit is 1,000V ee and the lower limit is E1VI.
I! or E2 VIE, whichever is larger, so the bias constraints are large.

Incidentally, the stability of the operation of a transistor is proportional to the magnitude of the signal amplitude. Therefore, in order to stabilize the operation of the transistor, if the transistor is operated in a saturated state to increase the signal amplitude, there are various problems such as a reduction in Q, the operation speed of the transistor, and the generation of saturated capacitance.

SUMMARY OF THE INVENTION Therefore, the present invention has been made to overcome the problems of the conventional circuits described above, and provides an oscillation circuit which is free from restrictions on signal amplitude due to bias and is capable of stable oscillation operation with a large signal amplitude. is the issue.

[Means to solve the problem]

In order to solve the above problems, an oscillation circuit made according to the present invention includes a pair of differentially connected transistors, and first and second transistors each having one output connected in series to the collector of each of the pair of transistors. a current mirror circuit; a third current mirror circuit in which each output is connected in series with the other output of the first and second current mirror circuits; the first current mirror circuit and the third current mirror; an oscillation circuit section comprising an oscillation element connected between a connection point with the circuit and a reference potential point; a feedback circuit provided between the connection point and one of the pair of transistors; and a capacitor at the connection point. a coupled variable reactance section; fourth and fifth current mirror circuits, one output of which is connected in series to one of the pair of outputs of the variable reactance section; and the fourth and fifth current mirror circuits. A reactance circuit comprising a sixth current mirror circuit in which each output is connected in series to the other output, and a connection point between the fifth current mirror circuit and the sixth current mirror circuit is connected to the connection point. It is characterized by having a section.

[For production]

In the above configuration, in the oscillation circuit section, the oscillation element is connected between the connection point between the first current mirror circuit and the third current mirror circuit and the reference potential point, and the signal at the connection point is connected to the feedback circuit. Since the oscillation width of the oscillation circuit is not limited by the bias, the oscillation width of the oscillation circuit is large. Therefore, the oscillation dynamic range becomes wider.

In addition, the input of the reactance circuit section is capacitor-coupled to the oscillation circuit section, and its output is coupled to the current mode oscillation circuit section, so the oscillation circuit section and the reactance circuit section are completely separated and do not interfere with each other. In addition, the permissible amplitude range of the reactance circuit section, that is, the dynamic range, is widened as well as the oscillation circuit.

Furthermore, as mentioned above, both the oscillation circuit section and the reactance circuit section have a wide dynamic range, so even if the saturation of the transistor in the oscillation circuit section is suppressed, a sufficient oscillation width can be obtained, and the operation speed of the transistor due to saturation will be reduced. Problems such as generation of capacitance are solved, and an oscillation circuit that can perform stable oscillation operation can be obtained.

(Example) Hereinafter, embodiments of the present invention will be described based on the drawings. .

FIG. 1 is a circuit diagram showing an embodiment of an oscillation circuit according to the present invention which can be effectively applied as a voltage controlled oscillation circuit (CO) of a PLL circuit. The positive feedback amplifier l1a includes a differentially connected transistor Q+ItQ+z, transistors Q r s to Q +s constituting the first to third constant current sources, and a first
Transistor Q+bt(L
t, and the transistor Q that constitutes the second current mirror circuit.
Il, Ql9, and transistors Qgo, Q! that constitute the third current mirror circuit. l and feedback transistor Qtz
, a bias transistor Q23, amplitude limiting diodes DI1 to I)+s, a feedback capacitor CI1, and bias resistors Rl1 and R, (2).

A common emitter of the differentially connected transistors Q++yQtt has a transistor Q as a first constant current source.
rz is connected, transistor Q. A diode-connected transistor Q + b of the first current mirror circuit is connected to the collector of the transistor QI! ? A diode-connected transistor Q r s of a second current mirror circuit is connected to the collector, respectively. The transistor Q + t of the first current mirror circuit is the transistor Q t + of the third current mirror circuit, and the transistor Q11 of the second current mirror circuit is the diode-connected transistor Q2 of the third current mirror circuit. are connected in series with the transistors Q I ? and transistor Q
The connection point of zI is connected to the base of the feedback transistor Q2, which is connected in series with the transistor Ql4 constituting the second constant current source, and the emitter of the transistor Qzt is connected to the differential voltage via the capacitor Cll. One of the connected transistors Q++sQtx is connected to the base of QtI. Also, bias transistor Q zz
and a transistor QCs as a third constant current source are connected in series, and the base of a differentially connected transistor Q*+yQ+z is connected to the connection point thereof and a bias potential is applied thereto.

1lb is an oscillation element made of, for example, a ceramic resonator, and the oscillation element 12 is a first current mirror? Transistor QI that makes up the circuit? and transistor Qz. constituting the third current mirror circuit. The oscillation circuit section 11 is connected to the connection point with the positive feedback amplification section 11a.

In addition, E. is the bias voltage that sets the current flowing through the transistors Qrs to QIS, and Etz is the transistor Q and Ql! The quasi-voltage, E, which sets the bias potential of
l3 is a reference voltage connected to 1m of the oscillation element 11a via a resistor Rl2, and sets the center potential of the oscillation output.

Note that the oscillation output can be taken out from point a or b in the figure via a capacitor.

In the above configuration, the differentially connected transistor QI
l and QI! The output of Q+1 is the output of transistors Q0 and Q l ? which constitute the first current mirror circuit. QI! is applied to the oscillation element 11a via QI!
The output of transistor QI. constitutes the second current mirror circuit. The current is applied to the oscillation element 11a through Q19 and transistors Qgo and Q2 constituting the third current mirror circuit.

? The resonating element 11a resonates in parallel around the reference voltage El3 applied via the resistor Rl3, and its resonant output signal is transmitted through the feedback transistor Q2 and the feedback capacitor C. through the differentially connected transistors Q and Q +
It has been returned to t.

Note that the oscillation element 11a described above becomes high impedance in the parallel resonance mode, and the oscillation width becomes infinitely wide.
The transistor always operates in a saturated state, but in order to prevent this from happening, a resistor R3 is added between the transistor and the reference voltage El3 to lower the impedance.

As described above, in the present invention, transistors Q + r, Q
+t and Q. Since the output of the oscillation circuit section 11 constituted by is coupled by the PNP output of the transistor Q4 and the NPN output of the transistor Q,
The upper limit of the oscillation dynamic range is Vcc Ml
's lower limit is diode [) + s and transistor Qtz
2■ Can conduct. It is extremely wide. Of course, the vibration limiting diode D. ~I) When +s is deleted, is the upper limit? Vcc and lower limit become vsy, respectively, and the dynamic range becomes wider. In addition, since the oscillation dynamic range is wide as described above, the resistor Rl3 inserted to lower the impedance can be of a minimum necessary large value, and the effect of not lowering the Q can be obtained. Also, for the same reason, the amplitude limiting diode D. ~D. 5 is also the minimum necessary. Reference numeral 12 denotes a variable reactance circuit section whose capacitance can be varied within the range of +C to 1C, and the variable reactance circuit section 12 is a level shift/low-pass filter (LP).
F) Consists of a circuit 12a and a reactance circuit 12b.

The level shift/LPF circuit section 12a is a transistor Q3.
1'--Q4. , diode D, . ,D. ,, resistance R
t I '= R t S, capacitor C! 1, 00, etc., the resistor R■9RtR is a bias resistor, and C! I
is a signal coupling capacitor, and a resistor R. ．． , R■ and the capacitor CWt determine the characteristics of the LPF, and the transistors Qss to Q4. constitutes a bias current source. The reactance circuit 12b includes transistors Qas to Q.
am, capacitor CS+, etc., transistor Q
4I and Q4z and capacitor Cal constitute a reactance section, and transistor Q.4I and Q4z and capacitor Cal constitute a reactance section. The output on the transistor Qaz side is +C, and the output on the transistor Qaz side is -C. The transistors Qas to Qab constitute a bi-differential control section that functions as a current sharing circuit, and for example, the output is controlled by +C by a control voltage Vc consisting of the output voltage of a phase comparison circuit of a PLL circuit.
Control is performed so that the side signal is ~O~-C side signal.

The variable reactance circuit section 12 further includes fourth to sixth
Transistors Qs+ to Qs constituting the current mirror circuit of
h, and the transistors Qax and Qa of the dual differential control section
The output of s is a diode-connected transistor QSI forming a fourth current mirror circuit, and the outputs of transistors Q44 and Q46 of the dual differential control section are diode-connected transistors forming a fifth current mirror circuit. The transistor Qst of the fourth current mirror circuit is connected in series with the transistor Qs+ of the fourth current mirror circuit, and the transistor QS4 of the fifth current mirror circuit is connected in series with the diode-connected transistor Qss of the sixth current mirror circuit. Each is connected in series with the transistor Qs& of the mirror circuit,
The bases of the transistors Qzt and Qss and one end of the oscillation element 1lb are connected to the connection point between the transistor QS4 and the transistor Qsi, respectively. In addition, EI
4 is the transistor Q3. , & Qsz.

As described above, the transistor Q44, which is one output of the variable reactance circuit section 12, and . The output of the transistor Qss of the fifth current mirror circuit and the transistor Qsa of the sixth current mirror circuit are transmitted, and the output of the transistor Qaz and Q4s, which is the other output, is transmitted to the transistor QsI and the transistor QsI of the fifth current mirror circuit. The current is applied to the oscillation circuit section ll through the transistor Qsth of the sixth current mirror circuit, and the variable reactance circuit section 12 can be considered as a variable capacitance element CVI connected to one end of the oscillation element 1lb as shown in FIG. Can be done. As explained above, in the oscillation circuit of the present invention, the input of the variable reactance circuit section 12 is coupled to the oscillation circuit section 11 through capacitor coupling, and the output is coupled via a current mirror circuit in a high impedance current mode.
Since the oscillation circuit section l1 and the variable reactance circuit section l2 are completely separated, the coupling with the oscillation element 1lb is ideally performed, and there is no interference between them in terms of impedance.

Further, the allowable amplitude of the variable reactance circuit section 12 is also the allowable amplitude of the oscillation circuit section 11, VCC-VB to 2V. Similarly, the range from Vcc to 0 due to the transistors Qsa and Qsa is wide and unrestricted by bias, so the oscillation circuit as a whole has a large amplitude and can operate stably.

〔effect〕

As explained above, according to the present invention, the oscillation width of the oscillation circuit section is not restricted by bias and becomes large, the oscillation dynamic range is wide, and the input of the variable reactance circuit section is capacitor-coupled to the oscillation circuit section. , the output is coupled to the oscillation circuit section in current mode, so the oscillation circuit section and the variable reactance circuit section are completely separated and do not interfere with each other. The range is wide as well as the oscillation circuit.

Furthermore, as mentioned above, since the dynamic range of both the oscillation circuit section and the variable reactance circuit section is wide, sufficient oscillation 11 can be obtained even if the saturation of the transistor in the oscillation circuit section is suppressed, and the operating speed of the transistor due to saturation, Problems such as the occurrence of saturated capacitance can be solved, and an oscillation circuit that can perform stable oscillation operation can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of an oscillation circuit according to the present invention, Fig. 2 is a circuit diagram showing an example of a conventional oscillation circuit, and Fig. 3 is a circuit showing an equivalent circuit of the oscillation element in Fig. 2. 4 is a circuit diagram showing an equivalent circuit of an oscillation element and a variable reactance circuit, and FIG. 5 is a graph showing impedance characteristics of the circuit shown in FIG. 4. l1...Oscillation circuit section, llb...Oscillation element, l2...
...Variable reactance circuit section, QII, Ql! ,QIt
h~QtIpQm+~QS&...transistor, Q2
2...Feedback transistor, C. ...Feedback capacitor.

Claims (1)

[Scope of Claims] A pair of differentially connected transistors, first and second current mirror circuits each having one output connected in series to the collector of each of the pair of transistors, a third current mirror circuit in which each output is connected in series to the other output of the second current mirror circuit; a connection point between the first current mirror circuit and the third current mirror circuit; and a reference potential point; an oscillation circuit section comprising an oscillation element connected between the two transistors, and a feedback circuit provided between the connection point and one of the pair of transistors; a variable reactance section capacitively coupled to the connection point; fourth and fifth current mirror circuits in which one output is connected in series to one of the pair of outputs of the reactance section, and each output is connected in series to the other output of the fourth and fifth current mirror circuits, respectively; and a reactance circuit section that connects a connection point between the fifth current mirror circuit and the sixth current mirror circuit to the connection point. oscillation circuit.