RU2450416C1 - Quartz crystal oscillator - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: quartz crystal oscillator includes quartz-crystal resonator, first amplifier inverter, two resistors, second amplifier inverter, capacitor, resistance divider.

EFFECT: accuracy improvement of current compensation for static capacitance of quartz-crystal resonator and decrease of signal transmitted through quartz-crystal resonator in broadband.

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Description

The invention relates to the field of electronic technology and can be used to generate electrical signals stabilized by electromechanical resonators, in particular in piezoresonance sensors with an operating frequency range from 10 kHz to 200 kHz.

The closest in technical essence to the claimed device is a crystal oscillator (see RF patent No. 2301491 of November 30, 2005, published on June 20, 2007, B.I. No. 17), containing a crystal, the first inverting amplifier, the input and output of which are interconnected through the first resistor, the second inverting amplifier, the input of which is connected to the first output of the capacitor.

The above device is the closest in technical essence to the claimed and therefore selected as a prototype.

The disadvantage of the prototype is the complexity of the settings to achieve accurate compensation of the current static capacitance of the quartz resonator, which leads to an increase in the transition process of establishing a stable generation mode, which in some cases is unacceptable.

The problem to be solved is the creation of a quartz oscillator with a short availability time for reaching a stable mode of operation.

Achievable technical result is to increase the accuracy of current compensation of the static capacitance of the quartz resonator and to reduce the transmitted signal through the quartz resonator in a wide frequency band.

To achieve a technical result in a crystal oscillator containing a crystal, the first inverting amplifier, the input and output of which are connected to each other through the first resistor, the second inverting amplifier, the input of which is connected to the first output of the capacitor, is new, that a resistive divider and a second a resistor, the first output of which is connected to the input of the first inverting amplifier, and the second output is connected to the first output (input) of the resistive divider and the output of the second inverter amplifier, the input of which is connected to the first output of the quartz resonator, the second output of which is connected to the output of the first inverting amplifier, the second output of the capacitor is connected to the second output (output) of the resistive divider, the third output of which is connected to a common point, while the output of the second inverting amplifier is device output.

The figure 1 shows a functional diagram of a crystal oscillator. The figure 2 presents the equivalent circuit of a quartz resonator.

The device comprises a quartz resonator 1, a first inverting amplifier 2, the input and output of which are interconnected through the first resistor 3, a second inverting amplifier 4, the input of which is connected to the first output of the capacitor 5, a resistive divider 6 and a second resistor 7, the first output of which is connected to the input of the first inverting amplifier 2, and the second output is connected to the first output (input) of the resistive divider 6 and the output of the second inverting amplifier 6, the input of which is connected to the first output of the quartz resonator 1, the second the output of which is connected to the output of the first inverting amplifier 2, the second output of the capacitor 5 is connected to the second output (output) of the resistive divider 6, the third output of which is connected to a common point, while the output of the second inverting amplifier 4 is the output of the device.

The accuracy of compensation of the current of the static capacitance of the quartz resonator 1 is improved by using a resistive divider 6. More accurate compensation is achieved by selecting the transmission coefficient of the resistive divider 6 and the capacitance of the capacitor 5.

The device operates as follows. A section of the circuit "A-G", consisting of a resistive divider 6, a capacitor 5, is used to neutralize the static capacitance C _{0 of the} resonator 1.

The voltage at the output of the first inverting amplifier 1, due to the current flowing through the second resistor 7 (R ₂ ), is equal to the product of the resistance value of the first feedback resistor 3 (R ₁ ) and the input current value equal to U _A / R ₂ (property of the inverting amplifier with a coefficient gain K >> 1 with negative feedback):

where R ₁ is the resistance value of the first resistor 3;

R ₂ is the resistance value of the second resistor 7;

U _A - alternating voltage (point of circuit A).

много больше входного сопротивления второго инвертирующего усилителя 4 (Z_Q>>Z_вx2; Z_C1>>Z_вx2), ток, протекающий через кварцевый резонатор 1 I_K, определяется суммой двух составляющихIn the case when the impedance of a quartz resonator 1 Z _Q and a compensating capacitor 5 equal to

much more than the input resistance of the second inverting amplifier 4 (Z _Q >> Z _bx2 ; Z _C1 >> Z _bx2 ), the current flowing through the quartz resonator 1 I _K is determined by the sum of the two components

where Z _in - the value of the input impedance of the second inverting amplifier 4;

U _B - alternating voltage applied to the quartz resonator 1 (point of circuit B);

Z _K - the impedance of the resonant branch of the quartz resonator 1;

R _K , L _K , C _K are the equivalent parameters of quartz resonator 1 (see figure 2).

имеют соизмеримые значения.The current component of the quartz resonator 1, due to its static capacitance C ₀ , reduces the real quality factor and the steepness of the phase-frequency characteristic of the resonator and, accordingly, affects the frequency stability of the generator. The strongest negative effect of the capacitive current of the quartz resonator 1 on the frequency stability of the generator is manifested in cases where the components of the capacitive current ωС ₀ U _B and the resonant current

have commensurate meanings.

The current flowing through the capacitor 5 is determined by the expression

where C ₁ - the value of the capacitance of the capacitor 5 (see figure 1);

To _affairs - the transmission coefficient of the circuit section "AB" (transmission coefficient of the resistive divider 6);

U _B - alternating voltage at the output of resistive divider 6 (point of circuit B);

U _A - alternating input voltage (point of circuit A).

The transmission coefficient of the resistive divider 6 is determined by the choice of resistance values included in its composition.

The compensation condition for the shunt effect of the static capacitance can be determined from the sum of the currents flowing through the static capacitance C _{0 of the} resonator and capacitor 4:

, отсюдаFrom equation (6) it follows

from here

or

At the resonant frequency of the resonator 1 under condition (5), (6), (7), the capacitive current through the capacitance C _{0 of the} resonator is neutralized by the antiphase current (4) through the capacitor 5 C ₁ and the voltage at the input of the second inverting amplifier 4 is determined by the expression

where Z _K is the impedance of the resonant branch of the quartz resonator 1;

Z _Bx2 - input impedance of the second inverting amplifier 4.

With the active nature of the input impedance Z _Vx = R _{Vx the} voltage at the output of the second inverting amplifier 4 is determined by the expression

where K _{y_inv2} is the gain of the second inverting amplifier 4.

The transfer coefficient of the plot "A - output of the second inverting amplifier 4" is determined from the expression (9):

The transfer coefficient K _n will have a maximum and real value at a frequency equal to the resonant frequency of the quartz resonator 1, for which Z _K = R _K.

To ensure stable operation of the generator, two conditions must be met:

- the condition of the balance of the amplitudes, in which the transmission coefficient of the undistorted signal in the positive feedback loop K _{n of the} generator should be greater than 1;

is the condition of the phase balance under which

where K _n is the total transmission coefficient at the generation frequency;

φ _n - phase shift in the plot "A is the output of the second inverting amplifier 4" at the generation frequency.

According to the invention, prototype generators were manufactured, tests of which confirmed their efficiency and effectiveness. Moreover, the first inverting amplifier 2 and the second inverting amplifier 4 are made on complementary pairs of CMOS transistors. The second inverting amplifier 4 may include an amplitude diode limiter circuit or an automatic gain control (AGC) circuit, which is used to limit the amplitude of the alternating voltage supplied to the quartz resonator 1.

Claims (1)

A quartz oscillator comprising a quartz resonator, a first inverting amplifier, the input and output of which are connected to each other through a first resistor, a second inverting amplifier, the input of which is connected to the first output of the capacitor, characterized in that an additional resistive divider and a second resistor are introduced, the first output of which is connected with the input of the first inverting amplifier, and the second output is connected to the first output (input) of the resistive divider and the output of the second inverting amplifier, the input of which is connected to the first output of a quartz resonator, the second output of which is connected to the output of the first inverting amplifier, the second output of the capacitor is connected to the second output (output) of the resistive divider, the third output of which is connected to a common point, while the output of the second inverting amplifier is the output of the device.

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