Generator

FIELD: electricity.

SUBSTANCE: generator contains electromechanical resonator and neutralising capacitor, differential staged based on two MOS-transistors with the same conductivity type, amplifier including in-series four complementary pairs of MOS-transistors, low-pass filter.

EFFECT: excluding permanent component of excitation voltage at resonator input and increasing amplification factor for amplifier.

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The invention relates to the field of electronic technology and can be used to generate electrical signals, stable Electromechanical resonators, in particular in piezoresonance sensors.

Known as the "Generator" (see RF patent №2453983 from 18.03.2011, published in B. I. No. 17 dated 20.06.2012), which contains the Electromechanical resonator and a neutralizing condenser, the first conclusions which are interconnected differential cascade MOS-transistors with the same conductivity type, the output of which is connected to the input of the amplifier, which is made in two complementary pairs of MOS transistors, the low-pass filter, whose input is connected to the output of the amplifier, and the output is connected to the common connection point of the first conclusions of the Electromechanical resonator and a neutralizing capacitor, and the amplifier is made of two stage, the first stage which covered a negative feedback and differential cascade added seven resistors, the first conclusions of the first, second, third and fourth resistors connected together and connected to the positive power bus and the negative power bus connected to the first conclusions of the fifth, sixth and seventh resistors, the second the conclusions of the fifth and sixth resistors connected to the gates of the first and second MOS transistors, cultorum conclusions of the fourth and first resistors and second findings of the Electromechanical resonator and a neutralizing capacitor, respectively, second, the findings of the second and third resistors is connected to the drains of the MOS transistors, the sources of which are connected together and connected to the second output of the seventh resistor, the output of the amplifier is the output device.

The above device is the closest to the technical nature of the claimed device and, therefore, selected as a prototype.

The disadvantages of the prototype are:

- instability of its frequency due to the change in the DC component of the excitation voltage when changing the operation mode of the amplifier stages under the influence of external factors in the operating supply voltage, ambient temperature, storage etc.);

a relatively significant time in working mode due to insufficient gain.

Solved technical problem is the creation of a generator with quartz customizados resonator with high stability of oscillation frequency and low time output in operating mode.

Achievable technical result is the elimination constant component of the excitation voltage at the input of the resonator and increasing the gain of the amplifier.

To achieve a technical result in the generator containing the Electromechanical resonator and a neutralizing condenser, the first conclusion is which are interconnected, differential cascade of two MOS transistors with the same conductivity type, the output of which through the first capacitor is connected to the input of the amplifier, which includes serially connected complementary pair of MOS transistors, the output of the amplifier is the output device and connected to the input of a lowpass filter in the differential cascade drains of the first and second MOS transistors are connected through first and second resistors to the positive power bus and to the first conclusions of the third and fourth resistors, the second set of conclusions which are connected with gates of the first and second MOS transistors and through the fifth and sixth resistors connected to the negative power bus and the first conclusion of the seventh resistor, the second terminal of which is connected with the origins of the first and second MOS transistors, the gates of which are connected with the second findings of the neutralizing condenser and Electromechanical resonator, respectively, what is new is that the amplifier is additionally introduced two complementary pairs connected with an existing series, the last of which through the eighth resistor connected to the output of the previous complementary pairs and connected in series through the ninth and tenth resistors connected to the input of the first complementary pair, the output of which is connected to the output of p is the following complementary pairs through an eleventh resistor, this common connection point of the ninth and tenth resistors via a second capacitor connected to the negative power bus, the output of the lowpass filter is connected across the inputs of the third capacitor with the common connection point of the first conclusions of the Electromechanical resonator and a neutralizing condenser.

Introduction to the generator, condenser and additional complementary pairs of MOS transistors in the amplifier eliminates the DC component of the excitation voltage at the input of the resonator and to increase the gain of the amplifier in the inventive generator. The output voltage of the generator is the input voltage of the lowpass filter and the excitation voltage is formed on the third capacitor and fed to the frequency control cavity. The lowpass filter is configured so that the first and third harmonics at the output was maximum.

The figure 1 presents a schematic diagram of the inventive device.

The figure 2 presents the equivalent circuit of the quartz crystal.

The figure 3 shows the dependence of the transfer characteristics of the FET temperature.

Figure 4 depicts a plot of the voltage signal at the input of the lowpass filter.

The figure 5 presents the spectrum of the signal at the input of the lowpass filter.

the figure 6 depicts a plot of the excitation voltage of the proposed generator.

The generator (see figure 1) contains the Electromechanical resonator 1 and a neutralizing condenser 2, the first conclusions which are interconnected differential cascade 3 two n-channel MOS transistors 4 and 5, the output of which through the condenser 6 is connected to the input of the amplifier 7, which includes serially connected complementary pair of MOS transistors 8, 9, while the output of the amplifier 7 is an output device and connected to the input of the lowpass filter 10, while in the differential stage 3 drains of n-channel MOS transistors 4 and 5 are connected through 11 and resistors 12 to the positive power bus 13 and the first conclusions 14 and 15 resistors, the latter findings are connected to gates 4 and 5 of the n-channel MOS transistors 16 and 17, the resistors connected to the negative power bus 18 and the first output resistor 19, the second terminal of which is connected to the sources 4 and 5 are n-channel MOS transistors, the gates of which are connected with the second findings of the neutralizing condenser 2 and Electromechanical resonator 1, respectively, in the amplifier 7 additionally introduced two complementary pairs of MOS transistors 20 and 21, connected to the existing complementary pairs 8 and 9 sequentially, with the output 21 of the complementary pair through a resistor 22 connected to the output of complementary pairs of MOSFETs 20 and through sequentially connect the n resistors 23, 24 connected to the input complementary pair 8, the output of which is connected to the output of complementary pairs of MOS transistor 9 through a resistor 25, while the common connection point of the resistors 23, 24 through the condenser 26 is connected to the negative power bus 18, while the sources of the p-channel MOS transistors included in complementary pairs 8, 9, 20, 21 connected to the positive power bus 13, and the sources of n-channel MOS transistors included in complementary pairs 8, 9, 20, 21 connected to the negative power bus 18 the output of low pass filter 10 is connected through a capacitor 27 to the common connection point of the first conclusions of the Electromechanical resonator 1 and a neutralizing condenser 2.

The output of the differential cascade 3, the aggregation point of the second output resistor 12 and a drain of n-channel MOS transistor 5 connected to the first output capacitor 6, the second terminal of which is connected to the input of the amplifier 7, the capacitor 6 is used for the galvanic isolation of the input of the amplifier 7 from the output circuits of the differential cascade 3. The lowpass filter 10 consists of two series-connected integrating RC-chains: 28-29, 30-31.

The device operates as follows. Differential cascade 3 is an amplifier constructed of two symmetrical shoulders, each of which represents an independent usilitel the th cascade. The amplifiers are connected sources of the transistors 4, 5 and resistor 19. When complete symmetry all the settings right and left sides of the differential cascade must be equal.

Differential cascade 3 can be calculated by analytical or semi-graphic method. When the current operating point, it is recommended to choose the value I_DZ(see figure 3). This amount of current of the transistor is the most suitable for transistors 4, 5 differential cascade 3, since the drift of the operating point slightly depends on the inaccuracy of matching identical pairs of field-effect transistors 4, 5. In addition, when calculating the differential cascade 3 it is necessary to achieve maximum gain useful (paraphase or differential) signal.

Through the quartz resonator 1 flows a current I_QZdetermined by the sum of two components:

where U_IN- AC input n is Prairie;

Z_K- impedance resonant branches of the quartz resonator 5 (QZ);

R_IN- input impedance differential cascade;

R_K, L_KC_Kequivalent parameters of the crystal (see figure 2).

Component of the current of the quartz resonator 1, due to its static container₀(see figure 2), distorts the frequency response and phase characteristics of the resonator and, as a consequence, reduces the real factor and the slope of the phase-frequency characteristics of the resonator and, therefore, affects the frequency stability of the generator.

Compensation current component of the static capacitance of the crystal resonator 1 is similar to prototype and is due to the capacitive current of the neutralizing condenser 2.

The value of the neutralizing capacity of the capacitor 2 is selected from the formula:

In practice C0 a very small value share pF), so

,X_C2>>R_IN

Therefore, the expression(6), (7), (10) have the form:

Due to the features of differe the social cascade 3 under the conditions (1), (2), (3), (4), (12), (13), (14), (15) common mode currents static capacitance of the crystal resonator 1 and a neutralizing condenser 2 compensate each other (transferred to the output of the differential cascade 3 with significant reduction).

The gain section of the first output of the quartz resonator 1 - input differential cascade 3" is equal to:

The amplification factor of the differential signal is equal to:

wherethe steepness of the transistor

differential output impedance.

In the amplifier 7 according to figure 1, the working point is set automatically, which leads to the stability of the amplifier. The working point for such inclusion lies at the intersection of the transfer characteristics of a complementary pair of MOS transistors 8 straight U_BX=U_O. Due to the high input resistance transistor of MOS structure, the position of the working point does not depend on the resistance of the resistors 23 and 24 if it is changed in the range of hundreds of Ohms to several tens of Mω. The gain value of the complementary pairs 8, 9 MOS transistors of at least 20. Additionally introduced complementary pairs 20, 21 having a gain, also any 20, and necessary to increase the overall gain of the amplifier 7, which is the 20⁴.

To the input of the lowpass filter 10 is supplied from the amplifier 7 rectangular pulse sequence, which he converts into a signal of a sine wave (or approximate the shape of a sine wave).

Consider the case when a rectangular pulse sequence is characterized by the following expression : t_And=T/2 (see figure 4).

The spectrum of such a signal is presented on figure 5. The analysis of the diagram shows that the amplitude of the even-numbered (2, 4, 6, etc. harmonics, minimum, and there is no need for suppression. However, the odd harmonics (3, 5, 7 etc) should be suppressed, so that only the first harmonic. In this case, the signal at the output of the lowpass filter 10 will be as close to the sine wave shape.

Harmonic frequencies are characterized by the equation:

As a lowpass filter consider a filter consisting of two links of simple RC circuits.

The gain of the lowpass filter 10 according to figure 1 is determined by the formula:

To simplify the calculation circuit made the following assumptions:

R28=R0=R,

C29=C31=C.

Then the expression for determining the transmission factor of the filter is:

Solving equation, find an expression for determining the bandwidth ƒ_Pfilter.

The lowpass filter 1 must be configured so that the ratio of amplitudes of harmonics 1 and 3 after passing through the filter was maximum.

The above explains the schedule shown in figure 6, which shows the waveform of the excitation voltage of the proposed generator using a lowpass filter 11 according to the proposed configuration, the gain of which the frequency of the resonator will be:

To ensure stable operation of the generator, you need to meet two conditions:

1) the condition of amplitude balance, which is that the natural frequency of the resonator should be the ratio of. In this case, the oscillation amplitude tends to increase up until the amplifier 7 misses in the nonlinear region, where there comes a limit amplitude;

2) the condition of balance of the phases, which is what the self-oscillations in a closed loop to occur if the transfer ratio open-loop system is a real value, i.e. the total phase shift differential cascade 3, the amplifier 7, the low pass filter 10 and the resonator 1 is equal to or a multiple of 2π. In this case, the amplifier 7 at the frequency of self-oscillations covered by positive feedback.

where K_Σ- the total gear ratio;

K_i, K_n- transfer coefficients of the i-th and n-th link in the positive feedback loop, respectively;

φ_Σ- total phase shift;

φ_i- phase shift introduced by the i-th element in the feedback circuit at the frequency of generation.

In the inventive generator can be roughly divided into three segments, determining the total gain and a total phase shift.

The first link is formed of a quartz-crystal resonator 1 and a differential cascade 3 transfer coefficient at the resonant frequency of the quartz resonator 1 is determined by the product of the expressions (16), (17) and is To₁=K_IN·_D=0,5 (K_IN=0,025;_D=20), and a phase shift φ₁close to the value of π (180°).

The second component is the amplifier 7, his transfer coefficient depends on the selected circuit option. In the variant according to figure 1, the transmission coefficient corresponds expression is s (18) _Y=160000, and the phase shift φ₂close to the value of 0 (360°).

The third element is a low pass filter 10, his transfer coefficient at the resonant frequency of the quartz resonator 1 is determined by the expression (24)₃=K_LPF=0.3 and a phase shift φ₃close to the value of -110° (250°).

In the inventive generator, according to figure 1, when the above values of the transmission coefficient and phase shift of each of the units, the value of the total gear ratio in the small-signal at a frequency equal to the resonant frequency of the resonator 1 will be K_Σ=24000, which provides the first condition (32) is the condition of amplitude balance". Timing phase generated by the lowpass filter 10 are compensated for by selecting an appropriate value of capacitance coupling capacitor 6. When this is the condition of balance of phases". Thus, the conditions (25) provides a robust generation at a frequency equal to the resonant frequency of the resonator 1 after the filing of the generator voltage.

The process of establishing oscillation generator starts with very small amplitudes of the sine wave, undistorted form output signals and ends with a rectangular signal generator output. However, the output signal generator is supplied to the lowpass filter 10, p the following which gets close to the sine wave shape (figure 6). This signal is the excitation voltage of the resonator 1.

In the inventive generator by introducing a capacitor and additional complementary pairs of MOS transistors in the amplifier is possible to eliminate the DC component of the excitation voltage at the input of the resonator and to increase the gain of the amplifier, to increase the stability of the oscillation frequency and to reduce the time of generator output in operating mode of generation.

The efficiency of the proposed technical solutions are experimentally tested and confirmed by testing existing layouts generator using the frequency control resonators with frequencies from 20 kHz to 200 kHz.

The generator containing the Electromechanical resonator and a neutralizing condenser, the first conclusions which are interconnected, differential cascade of two MOS transistors with the same conductivity type, the output of which through the first capacitor is connected to the input of the amplifier, which includes serially connected complementary pair of MOS transistors, the output of the amplifier is the output device and connected to the input of a lowpass filter in the differential cascade drains of the first and second MOS transistors are connected through first and second resistors to the positive power bus and to the first conclusions of the third and fourth resist the ditch, the latter findings are connected to the gates of the first and second MOS transistors and through the fifth and sixth resistors connected to the negative power bus and the first output of the seventh resistor, the second terminal of which is connected with the origins of the first and second MOS transistors, the gates of which are connected with the second findings of the neutralizing condenser and Electromechanical resonator, respectively, characterized in that the amplifier is additionally introduced two complementary pairs connected with an existing series, the last of which through the eighth resistor connected to the output of the previous complementary pairs and connected in series through the ninth and tenth resistors connected to the input of the first complementary pair, the output of which is connected to the output of subsequent complementary pairs through an eleventh resistor, with a common connection point of the ninth and tenth resistors via a second capacitor connected to the negative power bus, the output of the lowpass filter is connected across the inputs of the third capacitor with the common connection point of the first conclusions of the Electromechanical resonator and a neutralizing condenser.