RU2504892C1 - Generator - Google Patents

Abstract

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.

3 dwg

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.

The famous "Generator" (see RF patent No. 2453983 dated March 18, 2011, published in BI No. 17 dated June 20, 2012), which contains an electromechanical resonator and a neutralizing capacitor, the first conclusions of which are interconnected, a differential cascade on MOS transistors with the same type of conductivity, the output of which is connected to the input of the amplifier, which is made on two complementary pairs of MOS transistors, a low-pass filter, the input of which is connected to the output of the amplifier, and the output is connected to a common connection point of the first conclusions of the electromechanical a resonator and a neutralizing capacitor, while the amplifier is made in two stages, the first stage of which is covered by negative feedback, and seven resistors are additionally introduced into the differential stage, the first conclusions of the first, second, third and fourth resistors are combined and connected to the positive power bus, and the negative the power bus is connected to the first terminals of the fifth, sixth and seventh resistors, the second terminals of the fifth and sixth resistors are connected to the gates of the first and second MOS transistors, to the second th and the first terminal of the fourth resistor and to the second terminal of the electromechanical resonator and a neutralizing capacitor, respectively, the second terminals of the second and third resistors are connected to the drains of MOS transistors whose sources are tied together and connected to the second terminal of the seventh resistor, the amplifier output is the output device.

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

The disadvantages of the prototype are:

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

- a relatively significant time to enter the operating mode due to insufficient gain.

The technical problem to be solved is the creation of a generator with a quartz frequency-setting resonator with increased stability of the generation frequency and a short exit time to the operating mode.

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

To achieve a technical result in a generator containing an electromechanical resonator and a neutralizing capacitor, the first conclusions of which are connected to each other, a differential cascade on two MOS transistors with the same type of conductivity, the output of which through the first capacitor is connected to the input of the amplifier, including complementary pairs connected in series MOS transistors, the amplifier output is the output of the device and is connected to the input of the low-pass filter, while in the differential cascade of drains the first and second MOSFETs are connected through the first and second resistors to the positive power bus and to the first terminals of the third and fourth resistors, the second terminals of which are connected to the gates of the first and second MOSFETs and through the fifth and sixth resistors are connected to the negative power bus and the first the output of the seventh resistor, the second output of which is connected to the sources of the first and second MOS transistors, the gates of which are connected to the second terminals of the neutralizing capacitor and the electromechanical resonator, respectively It is new, that two complementary pairs connected to the existing ones are additionally introduced into the amplifier, the output of the last of which through the eighth resistor is connected to the output of the previous complementary pair and through the ninth and tenth resistors connected in series is connected to the input of the first complementary pair, the output which is connected to the output of the subsequent complementary pair through the eleventh resistor, while the common connection point of the ninth and tenth resistors through the second capacitor Keys to the negative supply rail, the lowpass filter output is connected via a third capacitor is further inputted with a common connection point of first terminals of the electromechanical resonator and the neutralizing capacitor.

The introduction into the generator of the capacitor and additional complementary pairs of MOS transistors in the amplifier eliminates the constant component of the excitation voltage at the input of the resonator and increases the gain of the amplifier in the inventive generator. The output voltage of the generator is the input voltage of the low-pass filter, and the excitation voltage is formed on the third capacitor and is supplied to the frequency-setting resonator. The low-pass filter is adjusted so that the ratio of the first and third harmonics at its output is maximum.

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

The figure 2 presents the equivalent circuit of a quartz resonator.

The figure 3 shows the dependence of the transfer characteristics of the field effect transistor on temperature.

The figure 4 shows a plot of the voltage signal at the input of the low-pass filter.

The figure 5 presents the spectrum of the signal at the input of the low-pass filter.

The figure 6 shows a plot of the excitation voltage of the inventive generator.

The generator (see Fig. 1) contains an electromechanical resonator 1 and a neutralizing capacitor 2, the first terminals of which are connected to each other, a differential stage 3 on two n-channel MOS transistors 4 and 5, the output of which is connected through the capacitor 6 to the input of the amplifier 7, including complementary pairs of MOS transistors 8, 9 connected in series, while the output of the amplifier 7 is the output of the device and connected to the input of the low-pass filter 10, while in the differential stage 3 the drains of the n-channel MOS transistors 4 and 5 are connected They are connected through 11 and 12 resistors to the positive power bus 13 and the first conclusions 14 and 15 of the resistors, the second conclusions of which are connected to the gates of 4 and 5 n-channel MOS transistors and through 16 and 17 resistors are connected to the negative power bus 18 and the first output of the resistor 19, the second terminal of which is connected to the sources of 4 and 5 n-channel MOS transistors, the gates of which are connected to the second terminals of the neutralizing capacitor 2 and the electromechanical resonator 1, respectively, two complementary pairs of MOS transistors 20 and 21 are additionally introduced into the amplifier 7, connected to the existing complementary pairs 8 and 9 in series, with the output 21 of the complementary pair through the resistor 22 connected to the output of the complementary pair of MOS transistors 20 and through the series-connected resistors 23, 24 connected to the input of the complementary pair 8, the output of which is connected to the output of the complementary MOS pair -transistors 9 through a resistor 25, while the common connection point of the resistors 23, 24 through a capacitor 26 is connected to the negative power bus 18, while the sources of p-channel MOS transistors included in the set Mental pairs 8, 9, 20, 21 are connected to the positive power bus 13, and the sources of n-channel MOS transistors that are part of the complementary pairs 8, 9, 20, 21 are connected to the negative power bus 18, low-pass filter output 10 is connected through a capacitor 27 to a common point of connection of the first terminals of the electromechanical resonator 1 and the neutralizing capacitor 2.

The output of the differential stage 3, the union point of the second output of the resistor 12 and the drain of the n-channel MOS transistor 5, is connected to the first output of the capacitor 6, the second output of which is connected to the input of the amplifier 7, the capacitor 6 is used for galvanic isolation of the input of the amplifier 7 from the output circuits of the differential cascade 3. The low-pass 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 built of two symmetrical arms, each of which is an independent amplification cascade. The amplifiers are interconnected by the sources of transistors 4, 5 and resistor 19. With full symmetry, all parameters of the right and left parts of the differential cascade must be equal to each other.

Differential cascade 3 can be calculated by analytical or graphoanalytical method. In this case, the current of the operating point is recommended to be selected equal to I _DZ (see figure 3). It is this current value of the transistor that is most suitable for transistors 4, 5 of the differential stage 3, since the drift of the operating points does not depend much on the inaccuracy of selecting an identical pair of field effect transistors 4, 5. In addition, when calculating the differential stage 3, it is necessary to achieve the maximum value of the gain (paraphase or differential) signal.

A current I _QZ flows through the quartz resonator 1, which is determined by the sum of two components:

where U _IN - alternating input voltage;

Z _K is the impedance of the resonant branch of the quartz resonator 5 (QZ);

R _IN - input impedance of the differential stage;

R _K , L _K , C _K - equivalent parameters of a quartz resonator (see figure 2).

The current component of the quartz resonator 1, due to its static capacitance C ₀ (see Fig. 2), distorts the frequency response and phase response of the resonator and, as a result, reduces the real quality factor and the steepness of the phase-frequency characteristic of the resonator and, accordingly, degrades the frequency stability of the generator.

Compensation of the current component of the static capacitance of the quartz resonator 1 is similar to the prototype and is carried out due to the capacitive current of the neutralizing capacitor 2.

The value of the capacitance of the neutralizing capacitor 2 is selected from the ratio:

In practice, C0 is a very small value (fractions of pF), therefore

,

, X_C2>>R_IN

,

, X _C2 >> R _IN

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

Due to the peculiarity of differential cascade 3, when conditions (1), (2), (3), (4), (12), (13), (14), and (15) are satisfied, the common-mode currents of the static capacitance of quartz resonator 1 and a neutralizing capacitor 2 cancel each other (transmitted to the output of the differential stage 3 with significant attenuation).

The transfer coefficient of the plot "the first output of the quartz resonator 1 is the input of the differential cascade 3" is equal to:

The gain of the differential signal is equal to:

- крутизна транзистора,Where

- transistor slope,

- дифференциальное выходное сопротивление.

- differential output impedance.

In the amplifier 7, according to figure 1, the operating point is set automatically, which determines the stability of the amplifier. The operating point with this inclusion lies at the intersection of the transfer characteristic of a complementary pair of MOS transistors 8 with a straight line U _BX = U _OUT . Due to the high input resistance of the transistors of the MOS structure, the position of the operating point does not depend on the resistance of the resistors 23 and 24 when it changes from hundreds of ohms to several tens of megohms. The gain of the complementary pairs of 8, 9 MOS transistors is not less than 20. Additionally introduced complementary pairs of 20, 21 have a gain also equal to 20, and are necessary to increase the overall gain of the amplifier 7, which is 20 ⁴ .

At the input of the low-pass filter 10, a rectangular pulse sequence is supplied from the amplifier 7, which it converts into a sinusoidal waveform (or close in shape to a sinusoid).

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

The spectrum of such a signal is shown in figure 5. From the analysis of the diagram it can be seen that the amplitude of the even (2, 4, 6, etc.) harmonics is minimal, and there is no need to suppress them. However, the odd harmonics (with numbers 3, 5, 7, etc.) must be suppressed as much as possible so that only the first harmonic remains. In this case, the signal at the output of the low-pass filter 10 will have a shape as close as possible to the sine wave.

Harmonic frequencies are characterized by the ratio:

As a low-pass filter, we consider a filter consisting of two links of the simplest RC chains.

The transmission coefficient of the low-pass filter 10 according to figure 1 is determined by the formula:

To simplify the calculation of the scheme, the following assumption is accepted:

R28 = R30 = R,

C29 = C31 = C.

Then the expression for determining the transmission coefficient of the filter has the form:

, находим выражение для определения полосы пропускания ƒ_П фильтра.Solving the equation

, we find the expression for determining the passband ƒ _{П of the} filter.

The low-pass filter 1 must be adjusted so that the ratio of the amplitudes of harmonics 1 and 3 after passing through the filter is maximum.

The above is illustrated by the graph shown in figure 6, which shows the waveform of the excitation voltage of the inventive generator using a low-pass filter 11, according to the proposed setting, the transfer coefficient of which at the resonator frequency will be:

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

. В этом случае амплитуда колебаний стремится возрастать до тех пор, пока усилитель 7 не попадает в нелинейную область, где наступает ограничение амплитуды;1) the condition of the balance of the amplitudes, which consists in the fact that the ratio

. In this case, the amplitude of the oscillations tends to increase until the amplifier 7 falls into the nonlinear region where the amplitude is limited;

2) the condition of phase balance, which consists in the fact that self-oscillations in a closed loop occur under the condition that the open-loop transmission coefficient is a real value, i.e. the total phase shift of the differential stage 3, amplifier 7, low pass filter 10 and resonator 1 is equal to or a multiple of 2π. In this case, the amplifier 7 at the self-oscillation frequency is covered by positive feedback.

where K _Σ is the total transmission coefficient;

K _i , K _n - transmission coefficients of the i-th and n-th links in the positive feedback loop, respectively;

φ _Σ is the total phase shift;

φ _i is the phase shift introduced by the ith link in the feedback loop at the generation frequency.

In the inventive generator, it is conditionally possible to distinguish three links that determine the total transmission coefficient and the total phase shift.

The first link is formed by a quartz resonator 1 and a differential cascade 3, its transmission coefficient at the resonant frequency of the quartz resonator 1 is determined by the product of expressions (16), (17) and is K ₁ = K _IN · K _D = 0.5 (K _IN = 0.025; K _D = 20), and the phase shift φ ₁ is close to the value equal to π (180 °).

The second link is the amplifier 7, its transmission coefficient depends on the selected circuitry option. In the embodiment, according to figure 1, the transmission coefficient corresponds to the expression (18) K _Y = 160000, and the phase shift φ ₂ is close to a value equal to 0 (360 °).

The third link is a low-pass filter 10, its transmission coefficient at the resonant frequency of the quartz resonator 1 is determined by the expression (24) K ₃ = K _{low-pass filter} = 0.3, and the phase shift φ ₃ is close to -110 ° (250 °).

In the inventive generator, according to figure 1, with the above values of the transmission coefficient and phase shift of each link, the value of the total transmission coefficient in the mode of a 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) - the condition of the "balance of amplitudes". The phase advance created by the low-pass filter 10 is compensated by selecting the appropriate value of the capacitance of the separation capacitor 6. In this case, the condition of "phase balance" is fulfilled. Thus, the fulfillment of conditions (25) ensures stable generation at a frequency equal to the resonant frequency of the resonator 1 after applying a supply voltage to the generator.

The process of establishing oscillations of the generator begins with very small amplitudes with a sinusoidal undistorted shape of the output signals and ends with a rectangular signal at the output of the generator. However, the generator output signal is fed to a low-pass filter 10, after which it acquires a shape close to a sinusoid (figure 6). This signal is the excitation voltage of the resonator 1.

In the inventive generator, due to the introduction of a capacitor and additional complementary pairs of MOS transistors into the amplifier, it is possible to exclude the constant component of the excitation voltage at the resonator input and increase the gain of the amplifier, increase the stability of the generation frequency and reduce the time the generator goes into the operating mode of generation.

The operability of the proposed technical solution has been experimentally verified and confirmed by testing existing models of the generator using frequency-setting resonators with frequencies from 20 kHz to 200 kHz.

Claims (1)

A generator containing an electromechanical resonator and a neutralizing capacitor, the first conclusions of which are connected to each other, a differential cascade on two MOS transistors with the same type of conductivity, the output of which through the first capacitor is connected to the input of the amplifier, which includes series-connected complementary pairs of MOS transistors, the output the amplifier is the output of the device and is connected to the input of the low-pass filter, while in the differential stage the drains of the first and second MOS transistors are connected They are connected through the first and second resistors to the positive power bus and to the first terminals of the third and fourth resistors, the second conclusions of which are connected to the gates of the first and second MOS transistors and through the fifth and sixth resistors are connected to the negative power bus and the first terminal of the seventh resistor, the second terminal which is connected to the sources of the first and second MOS transistors, the gates of which are connected to the second terminals of the neutralizing capacitor and the electromechanical resonator, respectively, characterized in that the additional Two complementary pairs are connected to the existing one in series, the output of the last of which through the eighth resistor is connected to the output of the previous complementary pair and through the ninth and tenth resistors connected in series is connected to the input of the first complementary pair, the output of which is connected to the output of the subsequent complementary pair through the eleventh a resistor, while the common connection point of the ninth and tenth resistors is connected to the negative power bus through the second capacitor, the output is fil Three low frequencies are connected through an additionally introduced third capacitor to a common point of connection of the first terminals of the electromechanical resonator and the neutralizing capacitor.

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