RU2479104C1 - Pulse generator of wobble frequency on schmitt triggers with switched direction of scanning by frequency - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device comprises a scanning unit representing a sweep generator setting the range and speed of scanning, and a generator unit controlled by voltage, which generates square-wave pulses with increasing or decreasing frequency of output pulses.

EFFECT: expansion of frequency scanning range.

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Description

The invention relates to pulsed technology, namely to pulsed generators on Schmitt triggers, and can be used in testing systems, devices, sensors and other objects in communication devices, measuring equipment and automation, as well as in separate units when constructing self-adjusting control systems, in biophysical information converters based on silicon chips, etc.

Known oscillator frequency circuits (GKCH) on analog and discrete elements, for example on operational amplifiers, moreover, on their basis meters for the amplitude-frequency characteristics of active and passive elements of electronic devices are mass-produced.

However, these are rather cumbersome devices that cannot be integrated into electronic circuits, and simple small-sized GKCH on digital elements, capable, for example, of integrating biophysical information sensors into chips, are probably not available at present.

The closest analogues of the invention are voltage controlled square wave (VCO) generators built on digital microcircuits - Schmitt triggers [1], and a linear pulse-width converter with a linear characteristic [2].

As a prototype taken the input unit of the source of frequency-modulated sound signals, given in [1, p.81-82, Fig.2.38], the electrical circuit of which is presented in figure 1.

The device generates rectangular pulses, the frequency of which periodically changes in a certain range, and is implemented on digital CMOS Schmitt triggers. It can be represented in the form of 2 blocks: a scan unit 1 that produces a time-varying (periodically increasing and falling with a scan frequency F _ra ) control voltage, and block 2, consisting of a pulse generator (VCO) controlled by this voltage, which generates pulses with a frequency of F. Thus, the sweep generator 1, periodically smoothly changing the voltage at its output within certain limits, sets the scanning frequency range of the generator 2.

The sweep generator 1 in the prototype consists of an uncontrolled generator of rectangular pulses on a Schmitt trigger and an integrating chain R ₂ -C ₂ , which generates a voltage for the voltage-controlled generator 2 (VCO) due to periodic charging and discharging of the capacitor C ₂ .

F frequency sweep _isolator values defined chain R ₁ -C _1, and the frequency of output pulses of the entire device F and the scan range determined by the values of resistors R, _y R, and capacitors C _1, C _2, C _3.

The width of the region of variation of the voltage across the capacitor C ₂ , equal to ΔU _c , which is the range of variation of the control voltage, is defined as ΔU _c = U _st -U _cn , where U _cv is the voltage of the upper and U _cn -lower levels on the integrating capacitor C ₂ , and connected with the sweep frequency F _ra and the parameters of the integrating chain R ₂ -C _{2 the} ratio:

where U _p - trigger voltage;

γ = T _and / T is the fill factor of the pulse stream from the generator of block 1,

where T _and is the pulse duration, T is the sweep period, T = 1 / F _sc ;

a = exp {- (F ₀ / F _dec )},

where F ₀ = 1 / (R ₂ C ₂ ) is the characteristic frequency of the integrating chain.

Figure 2 shows the dependence of the stress of the upper and lower U U _{CB CH} levels on the integrating capacitor C ₂ to the reduced sweep frequency F ₀ F _isolator.

The average voltage across the capacitor C ₂ remains constant and is determined by the ratio:

When using the standard CMOS Schmitt trigger in the scan generator circuit, y ~ 0.5.

As can be seen from figure 2, in the prototype when changing the sweep frequency, the amplitude of the deployment voltage ΔU _c on the capacitor C ₂ also changes. For example, at a low sweep frequency F _ra / F ₀ = _{n1, the} span of the control voltage ΔU _c.1 = U _{c max} -U _{c min is} greater than at a higher frequency corresponding to a larger value of _n2 .

Thus, the range of variation of the output frequency F turns out to depend on the reduced sweep frequency F _ra / F ₀ .

If you need to change the sweep speed (sweep frequency F _sw ) to maintain the scanning range at the output of the device, in addition to changing the value of the capacitor C ₁ or the resistance value of the resistor R _1, it is necessary to simultaneously change the parameters of the integrating chain R ₂ -C ₂ .

This is a significant disadvantage of the prototype.

Consider the work of the VCO. The dependence of the output frequency of the VCO from the control voltage is determined by the ratio:

Here

Where

k = (1 + R / R _y )

U _N , U _B - fixed voltage of the lower and upper thresholds of the Schmitt trigger at a supply voltage U _P ,

U _UPR - _control voltage at the input of the VCO,

R _y , R is the resistance of the control resistor at the input of the VCO and the resistance of the feedback resistor,

C is the timing of the capacitor of the VCO.

Qualitatively, the dependence of the frequency F on U _control for different ratios R _y / R is presented in figure 3. This dependence is a semblance of a family of downward parabolas. As can be seen from the figure, the sweep range for the VCO ΔU _c is determined by the voltage of the upper and lower levels on the integrating capacitor C ₂ , which depend on the frequency of the reduced sweep F _ra / F ₀ , and is located in the region of maximum frequencies in the ambiguity zone.

This is another disadvantage of the prototype.

Type of characteristics (figure 3), frequency values and the degree of expansion of the frequency range are determined by the ratio R _y / R.

It is seen that with an increase in the ratio R _y / R, the steepness of the curves decreases, i.e. the relative change in the scanning frequency range narrows. Thus, the prototype has the following main disadvantages:

- the frequency scanning region with increasing sweep speed is characterized by a narrowing region of the scanning frequency change due to a decrease in the control voltage range ΔU _c (Fig. 2);

- the law of change in the frequency of pulses F from time to time at the output of the device in the selected range is ambiguous (figure 3);

- the maximum value of the output frequency F lies within the scanning range (figure 3), and not on one of its boundaries;

- when switching from one sweep frequency to another in order to preserve the width of the range of output frequencies, it is necessary to simultaneously reconfigure all parameters of the circuit, changing the values of the resistances and capacities of the device.

The aim of this invention is a pulsed oscillator of oscillating frequency on Schmitt triggers with a switchable scanning direction in frequency, free from the listed disadvantages of the prototype.

The inventive device consists of 2 interacting units implemented on standard digital Schmitt CMOS triggers: scan unit 1, which plays the role of a scan generator that sets the range and speed of scanning, and a VCO unit 2, generating rectangular pulses inside this region with increasing or decreasing frequency F output pulses.

The electrical circuit of the proposed device is presented in figure 4.

The output of the Schmitt trigger of the scanner 1 through a timing resistor R ₃ and a shunting circuit consisting of a limiting resistor R _ogp1 and a diode D ₁ , with its cathode directed to the output of the trigger, is connected to the top terminal of the grounded timing driver capacitor C ₁ , in parallel with which a controlled voltage divider is connected from series-connected resistors R ₁ , R ₂₁ , ΔR, and the upper terminal of the resistor R _{1 is} connected to the upper terminal of the capacitor C ₁ and the input terminal of the resistor R _y VCO of block 2, the common terminal of the resistors R ₁ , R ₂₁ s connected to the input of the Schmitt trigger of block 1, and in parallel with the resistor ΔR, the output of the electronic key EC is connected, the input of which is connected to the output of the Schmitt trigger of block 1; the output of the Schmitt trigger of block 2, being both the output of the device, is connected to the changeover contact 3 of the forward and reverse switcher switch P, the upper contact 1 of which is connected to the output of the timing resistor R, the other terminal of which is connected to the upper terminal of the grounded timing driver C ₂ , the common terminal resistor R _y and the input of the Schmitt trigger of block 2, as well as with the output of the resistor R _оgp2 , the other terminal of which is connected to the anode of the diode D ₂ , the cathode of which is connected to terminal 2 of the switch P.

The operation of the claimed device depends on the choice of the direction of the frequency change in a given scanning range, determined by the switch P.

Consider the operation of the device for the upper position of the switch (contacts 1-3 closed), corresponding to a decreasing frequency in the forward sweep section (Fig. 5). Fig. 5a shows voltage plots in the scanning unit 1, and Fig. 5b represents the dependence of the output frequency on the main parameters of the circuit.

If a generator on a Schmitt trigger without a controlled divider were used as a sweep generator, then its output voltage would vary in the range from U _Н to U _В , numerically equal to the thresholds of the Schmitt trigger, regardless of the sweep frequency, i.e. would be in the ambiguity zone (figure 3). By appropriate selection of the parameters of the controlled voltage divider, the boundaries of the output voltage are “transferred” to the unambiguity region (U _H1 -U _в1 ) on the falling sections of the generated frequency versus the control voltage, and the scan itself starts from the upper value of the output frequency F _в corresponding to the voltage U _н1 , and ends with a minimum frequency F _n corresponding to the voltage U _in1 (decreasing frequency sweep).

In this mode, the inventive device operates as follows.

In actual scanning cycle (T _p) is charging the timing capacitor C ₁ to reach voltage values at the input of Schmitt its upper trigger threshold U _B. The voltage on the capacitor C ₁ due to the divider reaches a higher value of U _in1 , prompting the VCO to generate a frequency decreasing in time. During the entire sweep time T _{p the} electronic key EC is open, and the value of the lower arm of the divider R ₂ is equal to (R ₂₁ + ΔR). The relationship of voltage and divider parameters is determined by the ratio:

where R ₂ = R ₂₁ + ΔR.

After reaching the upper threshold of operation, the output voltage of the Schmitt trigger abruptly decreases to a logical zero, and the electronic key EC shorts the lower resistor of the divider ΔR, forming the lower boundary of the selected range U _n1 , determined by the ratio:

The capacitor C ₁ begins to be quickly discharged along the chain R _{оgp1 -Д 1} , forming a reverse sweep with a duration of T _ooh . The limiting resistor R _оgp1 protects the output of the Schmitt trigger from overload with an increased supply voltage.

After the voltage at the input of the Schmitt trigger has a lower threshold, it changes its state, a high voltage is set again at its output, and the next sweep cycle of the output frequency begins.

The operation of the device for the lower position of the switch (contacts 2-3 closed) proceeds similarly to the above, the difference lies in the different dependence of the output frequency of the VCO from the control voltage. For R _ogp2 << R _{y, the} output frequency of the VCO depends on the control voltage as follows:

F = F ₀ D

F ₀ = 1 / R _y C ₂ ;

Figure 6 qualitatively shows the given dependence. It can be seen that, in contrast to the previously considered case, the output frequency of the VCO increases with increasing control voltage. The operation of the claimed device in this mode proceeds similarly to the above.

An experimental qualitative check of the prototype of the oscillating frequency generator was carried out and its quantitative study in the simulation environment Multisim-10. The form of the obtained dependencies is shown in Fig.7.

Literature

1. Braga Newton S. 135 amateur radio devices on a single chip. Per. from English M .: DMK Press, 2007.

2. Zhugan L.I., Matveev V.N. Linear pulse-width converter with two outputs on digital microcircuits - Schmit trigger and two inverters. Patent for invention No. 2409891, 2011.

Claims (1)

A pulsed oscillator of oscillating frequency on Schmitt triggers with a switchable frequency scanning direction, comprising a scan unit and a voltage controlled oscillator (VCO), consisting of two Schmitt triggers, two time-setting capacitors, two diodes and two limiting resistors, characterized in that, with to generate pulses with a selectable scanning direction by frequency, the Schmitt trigger block 1 via scan output of timing resistor R ₃ and a shunt its chain consisting of restrictive ayuschego resistor R _ogr1 and diode D _1, its cathode directed to the output of the flip-flop, connected to the upper terminal grounded timing capacitor C ₁ in parallel is connected to controllable voltage divider of series connected resistors R _1, R _21, ΔR, the upper terminal of the resistor R ₁ connected to the upper terminal of the capacitor C ₁ and the input terminal of the resistor R _y VCO of block 2, the common terminal of the resistors R ₁ , R _{21 is} connected to the input of the Schmitt trigger of block 1, and the output of the electronic key of the EC is connected in parallel with the resistor ΔR, the input of which o associated with the output of the Schmitt trigger block 1; the output of the Schmitt trigger of block 2, being both the output of the device, is connected to the changeover contact 3 of the forward and reverse switcher switch P, the upper contact 1 of which is connected to the output of the timing resistor R, the other terminal of which is connected to the upper output of the grounding timing capacitor C ₂ , the common terminal the resistor R _y and the input of the Schmitt trigger of block 2, as well as with the output of the resistor R _ogp2 , the other output of which is connected to the anode of the diode D ₂ , the cathode of which is connected to terminal 2 of the switch P.

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