CN216904847U - Synchronous constant amplitude sawtooth generator based on mirror current source - Google Patents

Abstract

The utility model discloses a synchronous constant amplitude sawtooth wave generator based on a mirror current source, wherein a rectangular pulse is connected with a B pole of a T3 through R1, a +12V is connected with A6 pin of the A2 through an E-C pole of T2, a C-E pole of R2 and a C-E pole of T3 in turn, a +12V is connected with A6 pin of the A2 through an E-C pole of T1, a B, E pole of T1 is in short circuit, a C pole of T2 is connected with the ground through a capacitor C1, a C pole of T2 is simultaneously connected with A3 pin of A1, A6 pin of A1 is in short circuit with a2 pin thereof, A6 pin of A1 is simultaneously connected with a 5 pin of A1 through C5, a1 pin of A1 is connected with an 8 pin of A1 through C4, A6 pin of A1 is connected with the ground through R4 and C3 in turn, R4, the connection point of C3 is connected with pin 3 of A2, pin 2 of A2 is connected with pin 6 of A2 through R3 and C2 in turn, +12V is connected with pin 2 of A2 through R5 and R6 in turn, the connection point of R5 and R6 is connected with pin 6 of A2, and pin 6 of A1 outputs a sawtooth wave signal synchronous with the input rectangular pulse.

Description

Synchronous constant amplitude sawtooth generator based on mirror current source

Technical Field

The utility model relates to a technology of a sawtooth wave generator, in particular to a synchronous constant amplitude sawtooth wave generator based on a mirror current source.

Background

The sawtooth wave is one of common waveforms, and the waveform of a standard sawtooth wave firstly rises in a straight line, then falls off steeply, rises again, then falls off steeply, and repeats the steps, and is a non-sine wave, and is named as the sawtooth wave because the sawtooth wave has the waveform similar to a saw.

The fundamental principle of a sawtooth generator is the charge and discharge control of a capacitor, which can generate a sawtooth wave by charging a capacitor at a constant rate and then rapidly discharging the capacitor using a switch.

Usually, an operational amplifier can be used to form a sawtooth voltage generator, an integrating circuit composed of operational amplifiers is used to perform constant current charging on a capacitor, a linearly rising waveform can be obtained, a hysteresis comparator is used to compare the amplitude of the linearly rising waveform, and the capacitor is discharged after the peak value is reached, so that a sawtooth wave signal can be formed.

Although the operational amplifier circuit adopts various means to reduce the zero drift, the zero drift phenomenon still exists in certain environments, so the amplitude of a sawtooth wave signal generated by a common sawtooth wave generator circuit is unstable, but a sawtooth waveform pulse signal with very stable amplitude is required in certain circuit automatic control fields such as a pulse width modulation control system, and a constant amplitude sawtooth wave generator is required to be designed.

On the basis of a traditional sawtooth wave generator circuit, the design utilizes a mirror current source circuit to control an operational input signal, utilizes a comparator circuit to compare an operational output level value with a reference voltage, and the output of the comparator controls the operational input signal in reverse, so that the average value of the operational output signal is in a constant state, and synchronous and constant-amplitude sawtooth wave generation is realized.

Disclosure of Invention

The utility model aims to solve the technical problem of providing a sawtooth wave generator technology which has simple structure, low manufacturing cost and reliable use.

In order to achieve the above purpose, the present invention provides a synchronous constant amplitude sawtooth wave generator based on a mirror current source, wherein a rectangular pulse signal is connected with a base of a transistor T3 through a resistor R1, a +12V power supply is connected with an output terminal 6 pin of an operational amplifier a2 through an E-C electrode of a transistor T2, a resistor R2 and a C-E electrode of a transistor T3 in sequence, the +12V power supply is connected with an output terminal 6 pin of the operational amplifier a2 through an E-C electrode of a transistor T1, a base of the transistor T1 is short-circuited with a collector, a collector of the transistor T2 is connected with an operation ground through a capacitor C1, a collector of the transistor T2 is connected with a non-inverting input terminal 3 pin of an operational amplifier a1, an output terminal 6 pin of the operational amplifier a1 is short-circuited with an inverting input terminal 2 pin of the operational amplifier a1, an output terminal 6 pin of the operational amplifier a1 is connected with an output terminal 5 pin of the operational amplifier a1 through a capacitor C5, a pin 1 of the operational amplifier a1 is connected with a pin of an operational amplifier a1 through a capacitor C4, an output end 6 pin of the operational amplifier A1 is connected with a working ground through a resistor R4 and a capacitor C3 in sequence, a connection point of a resistor R4 and a capacitor C3 is connected with a non-inverting input end 3 pin of the operational amplifier A2, an inverting input end 2 pin of the operational amplifier A2 is connected with an output end 6 pin of the operational amplifier A2 through a resistor R3 and an inverting electrolytic capacitor C2 in sequence, a +12V power supply is connected with the working ground through a resistor 5 and a resistor R6 in sequence, a connection point of a resistor R5 and a resistor R6 is connected with an inverting input end 2 pin of the operational amplifier A2, and an output end 6 pin of the operational amplifier A1 outputs a sawtooth wave signal which is synchronous with an input rectangular pulse signal and has a constant amplitude.

Drawings

Fig. 1 and 2 are included to provide a further understanding of the present invention and form a part of the present application, and fig. 1 is a mirror current source operating principle; fig. 2 is a circuit diagram of a synchronous constant amplitude sawtooth generator.

Detailed Description

Mirror current source theory of operation: the mirror current source is composed of two transistors T with identical characteristics₀And T₁Is formed, as shown in FIG. 1, due to the transistor T₀Tube voltage drop ofU _CE0And b-e voltage thereofU _BE0Is equal to that at this timeU _CB=0, thereby enabling the transistor T to be secured₀Operating in an amplifying state without entering a saturation operating state, so that the transistor T₀Collector currentI _C0= β ₀ I _B0。

Due to T in FIG. 1₀And T₁B-e are equal, so that the base currents of the two transistors are equalI _B0= I _B1= I _BDue to the current amplification factor of the two transistorsβ ₀=β ₁=βSo that the collector currents of the two transistorsI _C0= I _C1= I _C= βI _B。

It can be seen that it is due to this particular connection of the circuit thatI _C1AndI _C0in mirror image relationship, the circuit is thus referred to as a mirror current source, in which the current through resistor RI _RIs used as a reference current and is used as a reference current,I _C1to supply the output current to the load.

When in useβWhen the current is far more than 2, the output currentI _CThis can be found by the following equation:

I_C≈I_R=(V_CC-V_BE)/R

therefore, when V_CCAnd when the value of the resistance R is determined, the current is outputI _C1Then determines, for the same reason, the reference currentI _RIncrease and output currentI _C1It must be increased.

Similar to the conventional sawtooth generator, the synchronous constant amplitude sawtooth generator is also a sawtooth pulse signal generator synchronized with the input pulse, and the electrical principle is shown in fig. 2, and it can be seen that the sawtooth generator is composed of a rectangular pulse signal input circuit, a common emitter amplifier circuit, a high frequency filter circuit, a mirror current source circuit, a voltage follower circuit, an integrating circuit, a comparator circuit, and the like.

Transistor T₃And a peripheral circuit constituting a common emitter amplifier, the rectangular pulse signal passing through an input resistor R₁Enter T₃The common emitter amplifier through the output resistor R of the collector₂Outputting the amplified rectangular pulse signal through a high-frequency filter capacitor C₁Filtering out interference signals, and sending the interference signals to an operational amplifier A₁The non-inverting input terminal of (1).

Transistor T₁、T₂Forming a mirror current source circuit, a transistor T₂The collector current is the output current of the mirror current source described in the above formulaI _CTransistor T₁Collector and operational amplifier A₂The current between the output ends is the reference current of the mirror current sourceI _RNote here that since comparator A₂There is a reference current as described in the designI _RThe value is not fixed, but follows the comparator A₂Inversion of output, reference currentI _RThe value is in the process of being adjusted at any time, which is due toI _RThe value is continuously adjusted, so that the operational amplifier A can be used₁The output sawtooth signal amplitude is in a relatively constant state, as will be described in more detail below.

Therefore, as can be seen from FIG. 2, the transistor T₃Is not only controlled by the input rectangular pulse signal, but also by the transistor T of the mirror current source circuit₂Control of the collector current.

In addition, it can be seen that in this design the common emitter amplifier is not driven from T₃But through a resistor R₂Output to operational amplifier A₁Inverting input terminal, so that transistor T₃And a resistance R₂The combination of the two can be actually regarded as an adjustable resistor, so that the transistor T is easier to understand₃The resistance value of the adjustable resistor is controlled by the input rectangular pulse signal and the reference current.

The larger the reference current is, the larger the adjustable resistor is, and the resistor R is₂The higher the amplitude of the pulse signal at the upper end is, the higher the amplitude is, the lower the amplitude is, the higher the amplitude is, the lower the amplitude is, and the amplitude is₁The higher the amplitude of the rectangular pulse wave formed after the high-frequency interference is filtered, so the operational amplifier A₁The higher the input signal level value.

Operational amplifier A₁Form an in-phase proportional operation circuit due to A₁The output end is directly connected with the inverting input end in a conducting way, so all output voltages are fed back to the inverting input end, the circuit introduces voltage series negative feedback, and the feedback coefficient is 1u _O=u _P=u _NTherefore, operational amplifier A₁The relationship between the output voltage and the input voltage is:

u _O=u _I

therefore, the in-phase proportional operation circuit forms a voltage follower circuit, a capacitor C₁The square pulse is the input voltage of the voltage follower, and the higher the input voltage of the follower is, the higher the output voltage of the follower is.

The output end of the voltage follower is connected with a resistor-capacitor network R₄/C₃The formed integral circuit forms the rising edge of the sawtooth wave signal.

The conventional sawtooth wave generating circuit can generate a sawtooth pulse signal from a rectangular pulse wave signal because the time constant of forward integration of an integrating circuit is far larger than the time constant of reverse integration, or the time constant of reverse integration is far larger than the time constant of forward integration, so that the rising slope and the falling slope of the output voltage are different greatly, and the sawtooth wave can be obtained.

Generally, the sawtooth wave generating circuit is obtained by making the integration paths of the integrating circuit in two directions different by using the unidirectional conductivity of the diode.

The design also needs to use an integrating circuit to form a sawtooth wave signal, and the charging process of a capacitor in the integrating circuit forms the rising edge of the sawtooth wave signal, which is the same as that of the traditional sawtooth wave generating circuit, but the forming of the falling edge of the sawtooth wave is greatly different from that of the traditional circuit.

As can be seen from FIG. 2, the capacitance C₁The rectangular pulse signal passes through a voltage follower and a resistor R₄To the capacitor C₃The charging and capacitor charging process forms a sawtooth wave rising edge curve, and the sawtooth wave falling edge curve is different from that of a traditional sawtooth wave generator circuit in that the sawtooth wave falling edge curve is amplified by an operational amplifier A₂The composed comparator is controlled.

The power supply voltage of 12V passes through a divider resistor R₅、R₆Form a DC voltage as the comparator A₂Reference voltage of inverting terminal, capacitor C₃Is connected to the comparator A₂In the same phaseThe input end and the output end of the comparator are connected with a mirror current source circuit transistor T₁The collector electrode of (1).

Based on the property that the voltage across the capacitor cannot change abruptly, it should be noted here as well that the comparator A₂Is in a continuously inverted state, and an electrolytic capacitor C₂Will cause comparator A to exist₂The reference voltage at the inverting terminal of the circuit is not a stable voltage value but is in a continuous change, A₂When the output is high, A₂Will be at a₂And outputting high level and superposing.

So comparator A₂The voltage follower A₁In the capacitor C₃Upper charging signalU _C3（U _C3Can be regarded as A₁Average value of output signal) with the reference voltage of the inverting terminal, the comparison result will change the reference current of the mirror source circuitI _RThereby forming a falling edge curve of the sawtooth wave signal, and the process is briefly as follows:

if the maximum value of the sawtooth signal outputted by the sawtooth generator reaches the expected amplitude (in this case, the comparator A is exactly the case)₂The reference voltage value of the inverting terminal), and then an infinitesimal amount is added, the comparator a₂When the output is inverted to a high level, the reference current of the mirror current source is reduced to almost '0', thereby controlling the output current of the mirror current sourceI _C2(transistor T)₂Collector current) is also almost "0", further controlling the common emitter amplifier T₁Through a resistance R₂Is almost '0', and the voltage follower A₁The output is abruptly changed to "0" (to be operationally a logic 0) to form the falling edge of the sawtooth signal.

The synchronization of the output sawtooth pulse with the input square wave pulse is easily understood as long as the resistor R₄Capacitor C₃The time parameter of the formed integrating circuit is reasonably selected, and the input rectangular wave pulse is in the range of 100 Hz-5 kHz, so that the input and output can be synchronized easily.

Follower A₁Output sawtooth wave signalIf the amplitude becomes large for some reason, comparator A₂The voltage at the same phase terminal becomes larger, A₂Outputting a high level, mirrored current source reference current I_RBecomes "0", follower A₁The average value of the output voltage decreases; on the contrary, if the amplitude of the output sawtooth wave signal is reduced, the voltage and current change phase of each reference point is reversed.

If the amplitude of the input rectangular wave pulse signal of the design is increased for some reason, the resistor R₂Increased output voltage, follower A₁The output will increase, which will result in comparator A₂Output voltage reversal, mirror current source reference current I_RBecomes "0", follower A₁The average value of the output voltage decreases; conversely, if the amplitude of the rectangular wave pulse signal is reduced for some reason, the above change is reversed.

Through the above analysis, the follower A can be found₁The output voltage amplitude of the voltage regulator is always in a relatively stable state.

The amplitude of the output sawtooth signal can be calculated as follows:

U_A1-6=R₆/(R₅+R₆)*2U_b

whereinU _A1-6For the amplitude of the output signal of the sawtooth wave, the circuit supplies power with a voltage ofU _b=12V。

Note that: resistance R₄Capacitor C₃The integral circuit is composed of a time constant of a sawtooth wave signal generation control system, if the time constant is too small, the rising edge of the sawtooth wave is easy to become a sine wave, and therefore the linearity of the output sawtooth wave signal is affected.

If the component value is shown in FIG. 2, the frequency range can reach 100 Hz-5 kHz, if a high-performance operational amplifier is used, the oscillation upper limit frequency can be further widened, and at this time, the capacitor C₁The capacity of (c) needs to be changed accordingly.

The power supply voltage of the circuitU _bAt 12V, the current consumption is less than 10 mA.

According to the design, on the basis of a traditional sawtooth wave generator, output current is controlled by output voltage through a comparator circuit, and the amplitude of an input signal is controlled by utilizing the characteristic that reference current of a mirror current source is equal to the output current, so that the synchronization and constant amplitude of a sawtooth wave signal are finally realized.

Claims (1)

1. A synchronous constant amplitude sawtooth generator based on a mirror current source is characterized in that: according to the sawtooth wave generator, a rectangular pulse signal is connected with the base of a transistor T3 through a resistor R1, a +12V power supply sequentially passes through an E-C pole of a transistor T2, a resistor R2 and a C-E pole of a transistor T3 to be connected with a working ground, a +12V power supply simultaneously passes through an E-C pole of a transistor T1 to be connected with the output end 6 pin of an operational amplifier A2, the base of the transistor T1 is in short circuit with the collector, the collector of the transistor T2 is connected with the working ground through a capacitor C1, the collector of the transistor T2 is simultaneously connected with the non-inverting input end 3 pin of an operational amplifier A1, the output end 6 pin of the operational amplifier A1 is in short circuit with the inverting input end 2 pin of the operational amplifier A1, the output end 6 pin of the operational amplifier A1 is simultaneously connected with the output pin 5 of the operational amplifier A1 through a capacitor C5, the 1 pin of the operational amplifier A1 is connected with the output pin of the operational amplifier A1 through a capacitor C4, the output end 6 pin of the operational amplifier A1 sequentially passes through a resistor R4 and a capacitor C3 to be connected with the working ground, and a resistor R4, The connecting point of the capacitor C3 is connected with the pin 3 of the non-inverting input end of the operational amplifier A2, the pin 2 of the inverting input end of the operational amplifier A2 is connected with the pin 6 of the output end of the operational amplifier A2 through the resistor R3 and the reverse electrolytic capacitor C2 in sequence, the +12V power supply is connected with the working ground through the resistor 5 and the resistor R6 in sequence, the connecting point of the resistor R5 and the resistor R6 is connected with the pin 2 of the inverting input end of the operational amplifier A2, and the pin 6 of the output end of the operational amplifier A1 outputs a sawtooth wave signal which is synchronous with the input rectangular pulse signal and has constant amplitude.

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