RU2705448C1 - Tunable rc oscillator - Google Patents

Abstract

FIELD: radio equipment.

SUBSTANCE: invention relates to radio equipment. RC oscillator comprises first and second terminals, first, second and third transistors, first, second and third resistors, first, second and third capacitors, first and second current sources, in order to provide the possibility of rapid change of frequency of formed sinusoidal oscillations and expansion of the range of frequency tuning, the first and second varicaps, the fourth and fifth resistors and the variable resistor are introduced. At that, change of frequency of generated sinusoidal oscillations is provided by changing capacitances of the first and second varicaps by changing levels of back voltages supplied to them by means of variable resistor, and wider range of frequency tuning is provided by selecting the first and second varicaps with a large value of overlapping ratio by capacitance.

EFFECT: possibility of rapid change of frequency of formed sinusoidal oscillations and expansion of frequency tuning range.

1 cl, 1 dwg

Description

The invention relates to radio engineering and can be used as a tunable source of sinusoidal oscillations, including in integrated circuits.

Known controlled generator of sinusoidal oscillations, containing an operational amplifier, AGC circuit, an electrically controlled switch, a low-pass filter, a variable resistor, two capacitors, a control pulse generator, a trigger and designed to generate sinusoidal oscillations in a wide frequency range with increased short-term frequency stability [a. from. USSR No. 1501244, MKI ⁴ Н03В 5/26. - Publ. in B.I., No. 30, 1989].

The disadvantages of this controlled generator of sinusoidal oscillations are:

1) the limited value of the maximum frequency of the generated oscillations due to the use of an operational amplifier in the generator circuit;

2) the presence of an additional generator of control pulses and an electrically controlled switch.

As a prototype of the invention is an RC generator [US Pat. No. 2666226 of the Russian Federation, IPC Н03В 5/26 (2006.01). - Publ. in B.I., No. 25, 2018], containing the first and second terminals, the first, second and third transistors, the first, second and third resistors, the first and second current sources, the first, second and third capacitors.

The disadvantage of this RC generator is the lack of the ability to quickly change the frequency of the generated sinusoidal oscillations.

The technical result of the proposed tunable RC-generator is the ability to quickly change the frequency of the generated sinusoidal oscillations and expand the range of frequency tuning.

The specified technical result is achieved by the fact that in the RC generator containing the first and second clamps, the first is the third transistors, the first is the third resistors, the first and second current sources, the first is the third capacitors, in order to enable the on-line change of the frequency of the generated sinusoidal oscillations and expansion of the frequency tuning range, the first and second varicaps are introduced, the first conclusions of which are connected through the first and second capacitors to the first conclusions of the first and second terminals, respectively, and the second of the second and second varicaps are connected to a common bus, a variable resistor, the first pin of which is connected to the first power bus, and the second pin to a common bus, fourth and fifth resistors, the first pins of which are connected to the first pins of the first and second varicap, respectively, and the second pins - to the middle terminal of the variable resistor.

The drawing shows a structural electrical diagram of the proposed tunable RC-generator.

The tunable RC generator contains the first 1 and second 2 terminals, the first 3, second 4 and third 5 transistors, the first 6 and second 7 resistors, the first 8 and second 9 current sources, the first 10 and second 11 varicaps, the first 12, second 13 and third 14 capacitors, third resistor 15, variable resistor 16, fourth 17 and fifth 18 resistors.

Tunable RC-generator operates as follows.

The first 6, second 7 resistors and second 11 varicaps in the tunable RC-generator circuit form an equivalent inductance L _e :

where R ₁ , R ₂ - the resistance of the first 6 and second 7 resistors, respectively;

C _VD2 - capacity of the second varicap 11.

The first varicap 10 forms with an inductance L _{e a} parallel oscillatory circuit tuned to a frequency ω ₀ :

where C _VD1 is the capacity of the first varicap 10.

When connecting power supplies with a voltage of +12 V, minus 12 V and minus 3 V, respectively, to the first, second and third power buses in the oscillatory circuit, sinusoidal oscillations with a frequency of ω ₀ occur. In order to maintain undamped oscillations in the oscillatory circuit, the transmission coefficient of the positive feedback circuit K _POS formed by the series connection of the third resistor 15 and the third capacitor 14 must satisfy the condition:

where S _VT3 - the steepness of the third transistor 5;

R ₃ is the resistance of the third resistor 15;

K ₀ is the gain of the cascade with a common base, performed on the third transistor 5;

R _oe is the resistance of the oscillatory circuit at a frequency ω ₀ equal to

where β ₁ , β ₂ are the transmission coefficients of the base currents of the first 3 and second 4 transistors, respectively.

To equalize the modes of the first 3, second 4 and third 5 transistors with alternating current, it is advisable to take: R ₂ = R ₁ , C _VD2 = C _VD1 . Then expression (2) will take the form

and the resistance of the third resistor 15, taking into account relations (3) and (4), must satisfy the condition:

The capacity of the third capacitor 14, providing galvanic isolation of the cascades made on the first 3, second 4 and third 5 transistors, must satisfy the condition:

Taking into account expression (2), it is possible to change the frequency ω _{0 of} setting the parallel oscillatory circuit by simultaneously changing the resistances of the first 6 and second 7 resistors and (or) capacitances of the first 10 and second 11 varicaps.

In the proposed tunable RC generator, a change in the frequency of sinusoidal oscillations at the generator output is achieved by changing the capacitances of the first 10 and second 11 varicaps by changing the levels of the reverse voltages supplied to them using a variable resistor 16. The value of the frequency range overlap coefficient k _per generated sinusoidal oscillations (ratio the maximum frequency of the output signal to the minimum frequency of the output signal) depends only on the value of the coefficient of overlap in capacitance k _with p applied varicaps and can be significantly more than ten. For example, when using KV116A varicaps, k _per ≥18.

Capacities of the first 12 and second 13 capacitors, providing galvanic isolation of the direct current of the first 10 and second 11 varicaps with cascades made on the first, second and third transistors 3-5, must satisfy the condition:

where C ₁ is the capacity of the first capacitor 12;

C ₂ - the capacity of the second capacitor 13;

C _VDmax - the largest value of the capacity of the applied varicaps.

The resistance of the fourth 17 and fifth 18 resistors included to reduce the effect of the resistance of the variable resistor 16 on the quality factor of the oscillatory circuit, is selected from the condition:

where R ₄ is the resistance of the fourth resistor 17;

R ₅ is the resistance of the fifth resistor 18;

ρ is the characteristic resistance of the oscillatory circuit:

where R = R ₁ = R ₂ .

Using the first 8 and second 9 current sources, the operating mode of the first 3, second 4 and third 5 transistors is set to direct current.

Claims (1)

A tunable RC generator containing first and second terminals, first, second and third transistors, a first resistor, the first output of which is connected to the emitter of the first transistor, a second resistor connected between the emitter of the second transistor and the emitter of the third transistor, the third resistor, the first, second and third capacitors, while the first terminal of the third resistor is connected to the emitter of the first transistor, the second terminal of the third resistor is connected to the first terminal of the third capacitor, the second terminal of which is connected to the emitter ru of the third transistor, the first terminals of the first and second capacitors are connected to the first terminals of the first and second terminals, respectively, the first current source, the first terminal of which is connected to the base of the first transistor, the collector of the third transistor and the first terminal of the first terminals, the second current source, the first terminal of which is connected to the collector of the first transistor, the base of the second transistor and the first terminal of the second terminals, the second terminal of the second current source and the collector of the second transistor are connected to the first power bus, the second the output of the first current source and the second output of the first resistor are connected to the second power bus, the base of the third transistor is connected to the third power bus, the second conclusions of the first and second terminals are connected to a common bus, characterized in that it contains the first and second varicaps, the fourth and fifth resistors, a variable resistor, while the first terminals of the first varicap and the fourth resistor are connected to the second terminal of the first capacitor, the first terminals of the second varicap and the fifth resistor are connected to the second terminal of the second capacitor, torye terminals of the fourth and fifth resistors connected to the intermediate tap of the variable resistor, a first terminal of the variable resistor connected to the first power line, a second terminal of the variable resistor and the second terminals of the first and second varactors are connected to a common bus.

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