Simple digital width modulation narrow pulse generation circuit

Abstract

The invention discloses a simple digital width modulation narrow pulse generation circuit, and relates to the technical field of electronic circuits. The circuit comprises a multivibrator, an RC series-parallel network, a digital adjustable stabilized voltage supply and a comparator. The multivibrator is composed of an NAND gate 1 and an NAND gate 2, outputs a rectangular wave signal to drive an RC series-parallel network, and generates a pinnacle pulse waveform on a resistor R3; the adjustable voltage-stabilized power supply is designed based on TL431, outputs adjustable stable voltage by controlling a binary resistance network, and is connected with the anti-phase end of the comparator; the in-phase end of the comparator receives a pinnacle pulse signal, and outputs a width-adjustable narrow pulse through dynamic threshold comparison. Through combination of RC charging and discharging characteristics and an adjustable threshold value, digital controllable adjustment of the pulse width from 30 ns to 660 ns is realized, and the circuit is simple in structure, low in cost and high in anti-interference performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of analog and digital hybrid circuits, and particularly relates to a narrow pulse generation circuit with simple digital pulse width modulation. Background Art

[0002] Narrow pulse signals are widely used in various fields, including communication, radar, computer buses, sensors, etc. Therefore, various narrow pulse signal generation circuits have been developed to meet various requirements. Traditional narrow pulse generation circuits mainly rely on monostable flip-flops or complex logic chips (such as FPGAs), and generally have problems such as low adjustment accuracy, high circuit complexity, and high cost. Therefore, there is an urgent need to develop a narrow pulse generation circuit with simple digital pulse width modulation to achieve high-precision and low-cost digital pulse adjustment. Summary of the Invention

[0003] Object of the Invention: To solve the above technical problems, the present invention provides a narrow pulse generation circuit with simple digital pulse width modulation. Through the collaborative design of a multivibrator, an RC charge and discharge network, a digitally adjustable regulated power supply, and a dynamic threshold comparison, the circuit structure is simplified, and high-precision digital pulse adjustment is achieved.

[0004] Technical Solution: A narrow pulse generation circuit with simple digital pulse width modulation provided by the present invention includes:

[0005] A multivibrator, which is composed of NAND gate 1 and NAND gate 2 connected in series, and is used to generate a periodic rectangular wave signal;

[0006] An RC series-parallel circuit, including a parallel combination of resistor R2 and capacitor C2, one end of which is connected to the output end of the multivibrator, and the other end is grounded after being connected in series with resistor R3;

[0007] A digitally adjustable regulated power supply, including a controllable precision voltage regulator TL431, resistor R4, resistor R6, and a binary resistor network composed of R51 - R5n. The cathode of TL431 is connected to the positive power supply through resistor R4, the anode of TL431 is grounded, and the resistors R51, R52, R53,..., R5n in the binary resistor network are respectively connected in parallel with switches K1, K2, K3,..., Kn. The binary resistor network is connected in series with resistor R6 and then connected in parallel between the reference terminal and the anode of TL431. Among them, the on / off states of switches K1 - Kn correspond to digital logic 0 / 1, and n is an integer not less than 4;

[0008] Comparator A, whose non-inverting input terminal is connected to the voltage dividing point of resistor R3, and the inverting input terminal is connected to the cathode of TL431, and is used to compare the sharp pulse with the adjustable voltage and output a narrow pulse signal with digitally adjusted pulse width.

[0009] Furthermore, in the multivibrator:

[0010] The input terminal of NAND gate 1 is fed back to the output terminal through resistor R1; the output terminal of NAND gate 2 is coupled to the input terminal of NAND gate 1 through capacitor C1 to form a self-excited oscillation loop, and its oscillation period is T = 2.2R1C1.

[0011] Further, in the RC series-parallel circuit: the resistance value of resistor R2 is 1 kΩ - 10 kΩ, and the capacitance value of capacitor C2 is 100 pF - 1 nF; the resistance value of resistor R3 is 500 Ω - 5 kΩ, which is used for voltage division and generating a spiked pulse waveform, and its peak voltage is 80% - 95% of the amplitude of the rectangular wave.

[0012] Further, the binary resistance network satisfies:

[0013] The resistance values of R51, R52, R53, …, R5n decrease in binary weight, and satisfy R51 = 0.5R6, R52 = 0.5R51, R53 = 0.5R52, and so on;

[0014] The output voltage of the digitally adjustable regulated power supply satisfies:

[0015]

[0016] where Ki is the switch state, 0 is closed, 1 is open, and the output voltage range is 2.5 V - 5 V.

[0017] Even further, the n = 4.

[0018] Further, the comparator A is a high-speed voltage comparator, its output terminal is connected to the positive power supply through a pull-up resistor, and the output signal drives an external load through a transistor buffer stage.

[0019] Further, the width adjustment range of the narrow pulse is 50 ns to 1 μs, and satisfies the relationship:

[0020]

[0021] where tw is the pulse width, R2C2 is the time constant of the RC series-parallel circuit, Vo is the output voltage of the adjustable regulated power supply, and Vpeak is the peak voltage of the spiked pulse.

[0022] Further, a filter capacitor with a capacitance value of 10 nF - 100 nF is connected in series between the inverting input terminal of the comparator A and the cathode of TL431, which is used to suppress high-frequency noise interference.

[0023] Further, a protection diode is connected in series between the output terminal of the multivibrator and the RC series-parallel circuit, its anode is connected to the output terminal of the multivibrator, and its cathode is connected to the RC series-parallel circuit, which is used to prevent reverse current impact.

[0024] Further, a filtering capacitor C with a capacitance value of 1 μF is connected in parallel between the reference terminal and the anode of the voltage regulator TL431 to stabilize the output voltage.

[0025] Further, the circuit is integrated on a single-layer PCB board with a total power consumption of less than 100 mW and is adapted to be powered by a 5V DC power supply.

[0026] The present invention also provides a digitally controlled monostable flip-flop, and the adjustment process of the narrow pulse generation circuit is as follows:

[0027] The multivibrator outputs a rectangular wave signal. When the rising edge of the rectangular wave signal occurs, the voltage of the capacitor C2 cannot change suddenly, and the voltage division of the resistor R3 is at a high level. As the capacitor C2 charges, the voltage division of the resistor R2 rises, and the voltage division of the resistor R3 starts to drop from the high level. Under the action of the periodic rectangular wave signal, the voltage division of the resistor R3 presents a spiked pulse waveform;

[0028] The digitally adjustable regulated power supply includes a controllable precision voltage regulator TL431, a resistor R4, a resistor R6, and a binary resistor network composed of R51 - R5n. The cathode of TL431 is connected to the positive power supply through the resistor R4, the anode of TL431 is grounded. After the resistors R51, R52, R53,..., R5n in the binary resistor network are respectively connected in parallel with the switches K1, K2, K3,..., Kn, the binary resistor network is connected in series with the resistor R6 and then connected in parallel between the reference terminal and the anode of TL431; the reference terminal R of TL431 is connected between the binary resistor network and the resistor R6. Among them, the on / off states of the switches K1 - Kn correspond to digital logic 0 / 1; the cathode of the controllable precision voltage regulator TL431 is connected to the resistor R5n and one end of the switch Kn to a comparator. By controlling the on / off of the switches K1, K2, K3,..., Kn, the regulated power supply outputs a voltage value within the range of 2.5V - 5V.

[0029] The non-inverting input terminal of the comparator obtains a signal with a spiked pulse waveform from the resistor R3 in the RC series-parallel circuit, and the adjustable regulated power supply is connected to the inverting input terminal of the comparator. When the voltage at the non-inverting input terminal of the comparator is higher than the voltage at the inverting input terminal of the comparator, the comparator outputs a high level, otherwise the comparator outputs a low level.

[0030] During the process of adjusting the voltage of the adjustable regulated power supply from a low voltage value to a high voltage value, the time for the comparator to output a high level decreases, the width of the positive pulse of the rectangular wave changes, becoming a rectangular waveform, and the width of the positive pulse also becomes narrower. By controlling the on / off of the switches K1, K2, K3,..., Kn, the voltage value of the adjustable regulated power supply can be accurately adjusted, the width of the positive pulse can be changed, and a narrow pulse with an adjustable width can be output.

[0031] Working principle: Multivibrator: Outputs a rectangular wave signal. The rising edge triggers the RC circuit to charge, and the voltage division of R3 instantaneously becomes high level. As C2 charges, the voltage division of R3 gradually decreases, forming periodic spike pulses. Adjustable regulated power supply: Adjusting R5 changes the threshold voltage of the comparator. When the spike pulse is higher than the threshold, the comparator outputs a high level; otherwise, it outputs a low level. Pulse width adjustment: When the threshold voltage increases, the high-level output time shortens and the pulse width becomes narrower.

[0032] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following remarkable advantages: (1) Digital precise adjustment, an n-bit switch provides 2^n levels of precision (e.g., a 4-bit switch steps 0.165625V), and the pulse width adjustment range is 30ns - 660ns; (2) Strong anti-interference ability. A filtering capacitor (1μF) is connected in parallel to the reference terminal of TL431, and a filtering capacitor is added to the input terminal of the comparator to suppress power supply noise; (3) Low implementation cost, only requiring general logic gates, TL431, and discrete components, with a cost lower than the traditional FPGA solution. Description of the drawings

[0033] Figure 1 It is a schematic diagram of a narrow pulse generation circuit with simple digital pulse width modulation of the present invention. Specific embodiments

[0034] The following further details the technical solution of the present invention through specific embodiments. However, it is necessary to point out that the following embodiments are only used for describing the content of the invention and do not constitute a limitation to the protection scope of the present invention.

[0035] A narrow pulse generation circuit with simple digital pulse width modulation, comprising:

[0036] A multivibrator, composed of two NAND gates connected in series, for generating a periodic rectangular wave signal;

[0037] An RC series-parallel circuit, including a parallel combination of resistor R2 and capacitor C2, one end of which is connected to the output terminal of the multivibrator, and the other end is grounded after being connected in series with resistor R3;

[0038] A digitally adjustable regulated power supply, including a controllable precision voltage regulator TL431, resistor R4, resistor R6, and a binary resistor network composed of R51 - R5n. The cathode of TL431 is connected to the positive power supply through resistor R4, the anode of TL431 is grounded, and the resistors R51, R52, R53,..., R5n in the binary resistor network are respectively connected in parallel with switches K1, K2, K3,..., Kn. The binary resistor network is connected in series with resistor R6 and then connected in parallel between the reference terminal and the anode of TL431; among them, the on / off states of switches K1 - Kn correspond to digital logic 0 / 1, and n is an integer not less than 4;

[0039] Comparator A, whose non-inverting input terminal is connected to the voltage-dividing point of resistor R3 and whose inverting input terminal is connected to the cathode of TL431, is used to compare the spiky pulse with the adjustable voltage and output a narrow pulse signal with digitized pulse width modulation.

[0040] The multivibrator is composed of NAND gate 1 and NAND gate 2, and its output terminal generates a periodic rectangular wave signal. The specific working process is as follows:

[0041] Rising edge stage of the rectangular wave: When the rectangular wave signal jumps from low level to high level, the voltage of capacitor C2 cannot change suddenly. At this time, the voltage division of resistor R3 instantaneously reaches a high level (close to the amplitude of the rectangular wave).

[0042] Capacitor charging stage: During the period when the rectangular wave maintains a high level, capacitor C2 slowly charges through resistor R2, and the charging current gradually decreases, resulting in the voltage division of resistor R3 starting to decrease exponentially from the high level.

[0043] Falling edge stage of the rectangular wave: When the rectangular wave jumps to a low level, capacitor C2 quickly discharges through resistor R2, and the voltage division of R3 returns to zero.

[0044] Formation of periodic spiky pulses: Driven by the continuous rectangular wave signal, the voltage division of resistor R3 presents a periodic spiky pulse waveform, whose peak voltage Vpeak = Vrectangular wave × R3 / (R2 + R3), and the decay time constant T = R2C2.

[0045] The adjustable regulated power supply is composed of (see Figure 1 ):

[0046] Connection of TL431: The cathode of TL431 is connected to the positive power supply (5V) through resistor R4, the anode is grounded, and the reference terminal is connected to the voltage division network.

[0047] Voltage division network: The binary resistor network is connected in series with a fixed resistor R6 (10 kΩ) and then connected in parallel between the reference terminal and the anode of TL431. The output voltage satisfies:

[0048]

[0049] where Ki is the switch state, 0 means closed, 1 means open, and the output voltage range is 2.5V - 5V.

[0050] By adjusting the closed and open states of K1, K2, K3,..., Kn, the output voltage can be accurately adjusted within the range of 2.5V to 5V.

[0051] Taking n = 4 as an example:

[0052] When the resistance values of R51, R52, R53, and R54 decrease in binary weight and satisfy R51 = 0.5R6, R52 = 0.5R51, R53 = 0.5R52, R54 = 0.5R53; when switches K1 - 4 are all closed, the output voltage is 2.5V;

[0053] When the resistance values of R51, R52, R53, and R54 decrease in binary weight and satisfy R51 = 0.5R6, R52 = 0.5R51, R53 = 0.5R52, R54 = 0.5R53; by controlling the on and off of switches K1 - 4, the voltage output can be realized digitally;

[0054] When the resistance values of R51, R52, R53, and R54 decrease in binary weight and satisfy R51 = 0.5R6, R52 = 0.5R51, R53 = 0.5R52, R54 = 0.5R53; when switches K1 - 4 are all open, the output voltage is 4.84375V.

[0055] Comparator working logic and pulse width adjustment:

[0056] Signal input: The non - inverting input terminal of comparator A is connected to the voltage - dividing point of resistor R3 to receive the spike pulse signal; the inverting input terminal is connected to the output terminal (Vo) of the adjustable regulated power supply.

[0057] Output logic: When the spike pulse voltage VR3 > Vo, the comparator outputs a high level; when VR3 < Vo, the comparator outputs a low level.

[0058] Pulse width adjustment mechanism:

[0059] Lowering the threshold voltage (lowering Vo): The time period during which the spike pulse exceeds the threshold is extended, and the output pulse width increases;

[0060] Raising the threshold voltage (raising Vo): The time period during which the spike pulse exceeds the threshold is shortened, and the output pulse width becomes narrower.

[0061] Mathematical relationship: The pulse width tw satisfies the relationship:

[0062]

[0063] where tw is the pulse width, R2C2 is the time constant of the RC series - parallel circuit, Vo is the output voltage of the adjustable regulated power supply, and Vpeak is the peak voltage of the spike pulse.

[0064] Taking n = 4 as an example to set parameters: Multivibrator: R1 = 10kΩ, C1 = 100pF, oscillation period T = 2.2R1C1 = 2.2×10^4×10^ - 10 = 2.2μs, output frequency f ≈ 454kHz;

[0065] RC network: R2 = 2 kΩ, C2 = 470 pF, R3 = 4 kΩ, Vpeak = 5 V (At the instant of the rising edge of the square wave, the capacitor C2 is equivalent to a short circuit, and the voltage division on the resistor R3 is equal to the amplitude of the square wave output by the multivibrator;

[0066] Digital voltage regulator: R6 = 1 kΩ, R51 = 500 Ω, R52 = 250 Ω, R53 = 125 Ω, R54 = 62.5 Ω.

[0067] Test data:

[0068] Switch combination 0000: Vo = 2.5 V, pulse width 660 ns;

[0069] Switch combination 1111: Vo = 4.84 V, pulse width 30.6 ns;

[0070] PCB layout and anti-interference design:

[0071] Key signal path: The RC network (R2, C2, R3) is close to the comparator input terminal to reduce the influence of parasitic capacitance; The TL431 of the adjustable voltage regulator and the voltage division network (R5, R6) are compactly arranged to avoid introducing noise.

[0072] Filter design: A filtering capacitor C3 (10 nF) is connected in series at the inverting input terminal of the comparator, and the cut-off frequency fc

[0073] = 1 / 2πRthC3 ≈ 160 kHz (Rth is the output impedance of TL431, 100 Ω); A capacitor C4 (1 μF) is connected in parallel at the reference terminal of TL431 to suppress the output voltage ripple (< 10 mV).

[0074] Taking a 4-bit switch as an example (n = 4), some of its output values are shown in the following table:

[0075] Switch K1 Switch K2 Switch K3 Switch K4 Output voltage Vo (V) 0 0 0 0 2.5 0 0 0 1 2.665625 0 0 1 0 2.8125 0 0 1 1 2.96875 0 1 0 0 3.125 0 1 0 1 3.28125 0 1 1 0 3.4375 0 1 1 1 3.59375 1 0 0 0 3.75 1 0 0 1 3.90625 1 0 1 0 4.0625 1 0 1 1 4.21875 1 1 0 0 4.375 1 1 0 1 4.53125 1 1 1 0 4.6875 1 1 1 1 4.84375

[0076] By adjusting the binary resistor network composed of R51 - R5n, during the process of the circuit adjusting from a low voltage value to a high voltage value, the high-level time of the comparator output decreases, the width of the positive pulse of the square wave changes, becoming a rectangular waveform, and the width of the positive pulse also becomes narrower. By controlling the on / off of the switches K1 - K4, the voltage value of the adjustable voltage regulator can be digitally changed, the width of the positive pulse is changed, and a narrow pulse with an adjustable width is output.

[0077] The above are only the preferred embodiments of the present invention. It should be noted that the present circuit uses a 4-bit switch. For those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, such as using an 8-bit switch and other methods. These improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A simple narrow pulse generating circuit with adjustable width, characterized in that: include: A multivibrator, composed of a NAND gate 1 and a NAND gate 2 connected in series, is used to generate a periodic rectangular wave signal; An RC series-parallel circuit includes a resistor R2 and a capacitor C2 connected in parallel, one end of which is connected to the output end of the multivibrator, and the other end is connected in series with a resistor R3 and then grounded; A digital adjustable voltage-stabilized power supply comprises a controllable precision voltage-stabilized source TL431, a resistor R4, a resistor R6 and a binary resistor network composed of R51-R5n, wherein the cathode of TL431 is connected to the positive electrode of the power supply through the resistor R4, the anode of TL431 is grounded, the resistors R51, R52, R53, ..., R5n in the binary resistor network are respectively connected in parallel with switches K1, K2, K3, ..., Kn, and the binary resistor network is connected in series with the resistor R6 and then connected in parallel between the reference end and the anode of TL431; wherein the on-off state of the switches K1-Kn corresponds to the digital logic 0 / 1, and n is an integer not less than 4; Comparator A, whose non-inverting input terminal is connected to the voltage dividing point of resistor R3 and whose inverting input terminal is connected to the cathode of TL431, is used to compare the peak pulse with the adjustable voltage and output a digitally width-adjusted narrow pulse signal.

2. The narrow pulse generating circuit according to claim 1, characterized in that: In the multivibrator: The input end of NAND gate 1 is fed back to the output end through resistor R1; the output end of NAND gate 2 is coupled to the input end of NAND gate 1 through capacitor C1, forming a self-excited oscillation loop, whose oscillation period is T=2.2R1C1.

3. The narrow pulse generating circuit according to claim 1, characterized in that: In the RC series-parallel circuit: The resistance value of resistor R2 is 1kΩ-10kΩ, the capacitance value of capacitor C2 is 100pF-1nF; the resistance value of resistor R3 is 500Ω-5kΩ, which is used to divide the voltage and generate a peak pulse waveform, and its peak voltage is 80%-95% of the rectangular wave amplitude.

4. The narrow pulse generating circuit according to claim 1, characterized in that: The binary resistor network satisfies: The resistance values ​​of R51, R52, R53, ..., R5n decrease according to the binary weight, and satisfy R51 = 0.5R6, R52 = 0.5R51, R53 = 0.5R52, and so on; The output voltage of the digital adjustable regulated power supply meets: Among them, Ki is the switch state, 0 is closed, 1 is open, and the output voltage range is 2.5V-5V.

5. The narrow pulse generating circuit according to claim 4, characterized in that: Said n=4.

6. The narrow pulse generating circuit according to claim 1, characterized in that: The comparator A is a high-speed voltage comparator, whose output terminal is connected to the positive pole of the power supply through a pull-up resistor, and the output signal drives the external load through a transistor buffer stage.

7. The narrow pulse generating circuit according to claim 6, characterized in that: The width adjustment of the narrow pulse satisfies the relationship: Among them, tw is the pulse width, R2C2 is the time constant of the RC series-parallel circuit, Vo is the output voltage of the adjustable voltage-regulated power supply, and Vpeak is the peak voltage of the peak pulse.

8. The narrow pulse generating circuit according to claim 1, characterized in that: A filter capacitor with a capacitance of 10nF-100nF is connected in series between the inverting input terminal of the comparator A and the cathode of TL431 to suppress high-frequency noise interference.

9. The narrow pulse generating circuit according to claim 1, characterized in that: A protection diode is connected in series between the output end of the multivibrator and the RC series-parallel circuit, wherein the anode of the protection diode is connected to the output end of the multivibrator and the cathode of the protection diode is connected to the RC series-parallel circuit to prevent reverse current impact.

10. The narrow pulse generating circuit according to claim 1, characterized in that: A filter capacitor with a capacitance of 1 μF is connected in parallel between the reference terminal and the anode of the TL431 to stabilize the output voltage.

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