CN109004919B - Current/frequency conversion circuit and conversion method based on triangular wave modulation - Google Patents

Abstract

The invention relates to a high-precision current/frequency conversion circuit and a conversion method based on triangular wave modulation, wherein the high-precision current/frequency conversion circuit comprises a main integrator, the input end of the main integrator is an input current end, the output ends of the main integrator and a triangular wave generation circuit are connected with the input end of a comparator, the output end of the comparator is connected with one input end of a digital processing circuit, the two output ends of the digital processing circuit are respectively connected with the control end of an ultra-high-speed switching circuit and the input end of an output circuit, the input end of the ultra-high-speed switching circuit is connected with the output end of a constant current source circuit, the output end of the ultra-high-speed switching circuit is connected with the input end of the main integrator, the output end of a shaping circuit is connected with the other input end of the digital processing circuit, and the input end of the shaping circuit is connected with the output end of the triangular wave generation circuit. The invention solves the problems of high debugging difficulty, high requirements for debugging personnel and incapability of meeting the requirement of mass production in the current production and debugging process.

Description

Current/frequency conversion circuit and conversion method based on triangular wave modulation

Technical field

The present invention is in the technical field of analog-digital hybrid circuits, and specifically relates to current/frequency conversion circuits and conversion methods based on triangular wave modulation.

Background technique

The current/frequency conversion circuit is one of the important components of the inertial navigation system. It is used together with the accelerometer in the inertial navigation system to convert the output current of the accelerometer into a digital pulse signal proportional to it. At present, current/frequency conversion circuits using the charge balance principle are widely used. In the traditional method, the threshold level compared with the main integrator uses a fixed threshold level. When the input current signal is large, the constant current source switches over a large number of times. Since the transition time during the constant current source switching process is the main factor affecting the conversion accuracy, its accuracy is difficult to achieve the ideal target. Compensation or digital calibration methods are usually used for compensation. However, the process is complex, the debugging workload is large, and the requirements for components are high. . Therefore, it is necessary to improve the traditional circuit structure to mechanically reduce the error caused by the above-mentioned transition process, improve circuit accuracy, and reduce the difficulty of debugging.

Contents of the invention

The main purpose of the present invention is to provide a current/frequency conversion circuit and conversion method based on triangular wave modulation, aiming to reduce the overall switching operating frequency of the circuit, mechanically reduce errors caused by the transition process, improve circuit accuracy, and reduce debugging difficulty.

In order to achieve the above objectives, the present invention proposes a current/frequency conversion circuit based on triangular wave modulation, including a main integrator, a comparator, a digital processing circuit, a shaping circuit, an ultra-high-speed switching circuit, a constant current source circuit, an output circuit and a triangular wave generation circuit, the input terminal of the main integrator is the input current terminal, the output terminals of the main integrator and the triangle wave generating circuit are connected to the input terminal of the comparator, the output terminal of the comparator is connected to one input terminal of the digital processing circuit, and the digital processing circuit The two output terminals of the circuit are respectively connected to the control terminal of the ultra-high-speed switching circuit and the input terminal of the output circuit. The input terminal of the ultra-high-speed switching circuit is connected to the output terminal of the constant current source circuit. The output terminal of the ultra-high-speed switching circuit is connected to the main integrator. The input end of the device is connected, the output end of the shaping circuit is connected to the other input end of the digital processing circuit, the input end of the shaping circuit is connected to the output end of the triangular wave generating circuit; the triangular wave generating circuit includes a frequency division circuit, a threshold integration amplifier circuit and a crystal oscillator , the input terminal of the frequency dividing circuit is connected to the input terminal of the shaping circuit through the crystal oscillator, the output terminal of the frequency dividing circuit is connected to the input and output of the threshold integral amplifier circuit, and the output terminal of the threshold integral amplifier circuit is connected to the input terminal of the comparator.

In one embodiment of the present application, the triangular wave generating circuit includes a frequency dividing circuit, a threshold integration amplifier circuit and a crystal oscillator. The input end of the frequency dividing circuit is connected to the input end of the shaping circuit through the crystal oscillator. The output end of the frequency dividing circuit It is connected to the input and output of the threshold integral amplifier circuit, and the output terminal of the threshold integral amplifier circuit is connected to the input terminal of the comparator.

In one embodiment of the present application, the main integrator includes a precision operational amplifier N1, an integrating capacitor Cf1, a transistor VJ1 and a transistor VJ2. The non-inverting input terminal of the precision operational amplifier N1 is grounded, and its inverting input terminal is connected through a resistor RJ1 As the input current terminal, the output terminal of the precision operational amplifier N1 is connected to the input terminal of the comparator through the resistors RJ2 and RJ3 in turn. The bases of the transistor VJ1 and the transistor VJ2 are connected at the node between the resistor RJ2 and the resistor RJ3. The collector of VJ1 is connected to the positive pole of the power supply, the collector of transistor VJ2 is connected to the negative pole of the power supply, the emitters of transistor VJ1 and transistor VJ2 are connected to the input end of the comparator and one end of the integrating capacitor Cf1 through resistors RJ4 and RJ5 respectively. The other end is connected to the inverting input end of the precision operational amplifier N1; among them, the transistor VJ1 is an N-type transistor, and the transistor VJ2 is a P-type transistor.

In one embodiment of the present application, the threshold integration amplifier circuit includes an integrator N2 and a proportional operational amplifier N3. The non-inverting input terminal of the integrator N2 is connected to ground, and its inverting input terminal is connected to the output of the frequency dividing circuit through a resistor RT1. terminal is connected, the output terminal of the integrator N2 is connected to the inverting input terminal of the proportional operational amplifier N3 through the resistor RT2, the non-inverting input terminal of the proportional operational amplifier N3 is connected to ground, and the output terminal of the proportional operational amplifier N3 is connected to the comparator.

In one embodiment of the present application, the ultra-high-speed switching circuit is composed of transistors V1 and V2, a field effect transistor V3 and peripheral circuits. The base of the transistor V1 is connected in parallel with the digital processing circuit through a resistor R1 and a capacitor C1. The output end is connected, the emitter of the triode V1 is connected to the power supply, the collector of the triode V1 is connected to the gate of the field effect transistor V3 through the resistor R2; the collector of the triode V2 is connected to the gate of the field effect transistor V3, and its emitter Connected to the power supply, its base is connected to the node between capacitor C1 and resistor R1 through capacitor C3. The source and gate of field effect transistor V3 are the output terminals of the ultra-high-speed switching circuit; one end of capacitor C2 is connected to resistor R2 and the transistor Between the collector of V1, the other end of the capacitor C2 is connected to the gate of the field effect transistor V3; among them, the transistor V1 is a P-type transistor, and the transistor V2 is an N-type transistor.

This application also discloses a conversion method of a current/frequency conversion circuit based on triangular wave modulation, which is used for the current/frequency conversion circuit based on triangular wave modulation as described in any one of the above, which includes the following steps:

(1) The constant current source circuit and the input current are continuously integrated and reset through the main integrator to generate a periodic sawtooth wave integrated voltage;

(2) The integrated voltage is compared with the threshold level through a comparator and then the integrated voltage is digitized to form a high and low pulse waveform;

(3) The pulse waveform is shaped by the digital processing circuit according to the output frequency of the shaping circuit, so that the pulse width and frequency of the pulse wave are synchronized to an integer multiple of the frequency output by the shaping circuit, and is simultaneously output by the digital processing circuit The pulse controls the on and off of the ultra-high-speed switching circuit, realizes the disconnection and access of the constant current source circuit, and controls the integration and reset time of the main integrator.

It can be seen from the above technical solution that the high-precision current/frequency conversion circuit based on triangular wave modulation of the present invention reduces the overall switching operating frequency of the circuit and uses ultra-high-speed switches composed of discrete devices to mechanically reduce errors caused by the transition process. , improve circuit accuracy. The current/frequency conversion circuit provided by the invention can achieve higher accuracy without compensation, which solves the current problems of difficulty in debugging during production debugging, high requirements on debugging personnel, and inability to meet mass production needs.

Description of drawings

The present invention will be described in detail below with reference to specific embodiments and drawings, wherein:

Figure 1 is a circuit principle block diagram of the present invention;

Figure 2 is a circuit diagram of the main integrator of the present invention;

Figure 3 is a circuit diagram of the threshold integration amplifier circuit of the present invention;

Figure 4 is a circuit diagram of the ultra-height switch circuit of the present invention;

FIG5 is a waveform diagram of working signals of the circuit of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings:

As shown in Figure 1, the high-precision current/frequency conversion circuit based on triangular wave modulation in this embodiment includes a main integrator 1, a comparator 5, a digital processing circuit 7, a shaping circuit 6, an ultra-high-speed switching circuit 8, and a constant current source. Circuit 9, output circuit 10 and triangular wave generating circuit, the input end of the main integrator 1 is the input current end, the output end of the main integrator 1 and the triangular wave generating circuit is connected to the input end of the comparator 5, the output end of the comparator 5 is connected to One input terminal of the digital processing circuit 7 is connected, and two output terminals of the digital processing circuit 7 are respectively connected to the control terminal of the ultra-high-speed switching circuit 8 and the input terminal of the output circuit 10. The input terminal of the ultra-high-speed switching circuit 8 is connected to the constant current source. The output terminal of the circuit 9 is connected, the output terminal of the ultra-high-speed switching circuit 8 is connected to the input terminal of the main integrator 1, the output terminal of the shaping circuit 6 is connected to the other input terminal of the digital processing circuit 7, and the input terminal of the shaping circuit 6 is connected to The output terminal of the triangle wave generating circuit is connected.

The output of the main integrator 1 is connected to an input of the comparator 5 and compared with the other threshold level of the comparator 5. The other threshold level is a low-frequency triangular wave. The low-frequency triangular wave is generated by the threshold integral amplification circuit 4. The threshold integral amplification The input of circuit 4 is a 16KHz low-frequency square wave signal, which is obtained from the crystal oscillator through the frequency dividing circuit 3. One output of the digital processing circuit 7 connects the constant current source circuit 9 to the input end of the main integrator 1 by controlling the ultra-high-speed switching circuit 8, and controls the on-off of the ultra-high-speed switching circuit 8 according to the output of the digital processing circuit 7. The crystal oscillator The 128KHz frequency standard signal generated by 2 is shaped by the shaping circuit and then input to the digital processing circuit 7, and the output circuit 10 is controlled to generate a pulse output.

The triangular wave generating circuit includes a frequency dividing circuit 3, a threshold integral amplifier circuit 4 and a crystal oscillator 2. The input end of the frequency dividing circuit 3 is connected to the input end of the shaping circuit 6 through the crystal oscillator 2. The output end of the frequency dividing circuit 3 is connected to the threshold integral amplifier circuit 4. The output terminal of the threshold integration amplifier circuit 4 is connected to the input terminal of the comparator 5 .

As shown in Figure 2, the main integrator 1 includes a precision operational amplifier N1, an integrating capacitor Cf1, a transistor VJ1 and a transistor VJ2. The non-inverting input terminal of the precision operational amplifier N1 is grounded, and the inverting input terminal of the precision operational amplifier is used as the input current through the resistor RJ1. terminal, the output terminal of precision operational amplifier N1 is connected to the input terminal of comparator 5 through resistors RJ2 and RJ3 in turn. The bases of transistor VJ1 and transistor VJ2 are connected at the node between resistor RJ2 and resistor RJ3. Transistor VJ1 and transistor VJ2 The collector is connected to the power supply. The emitters of transistor VJ1 and transistor VJ2 are connected to the input end of comparator 5 and one end of integrating capacitor Cf1 through resistors RJ4 and RJ5 respectively. The other end of integrating capacitor Cf1 is connected to the inverting terminal of precision operational amplifier N1. Input connection.

As shown in Figure 3, the threshold integral amplifier circuit 4 is composed of an integrating circuit composed of a front-stage integrator N2 and a proportional operational amplifier circuit composed of a subsequent-stage proportional operational amplifier N3. The non-inverting input terminal of the integrator N2 is grounded, and the inverse input terminal of the integrator N2 is grounded. The phase input terminal is connected to the 3 output terminal of the frequency division circuit through resistor RT1. The output terminal of integrator N2 is connected to the inverting input terminal of proportional operational amplifier N3 through resistor RT2. The non-inverting input terminal of proportional operational amplifier N3 is connected to ground. The proportional operational amplifier The output of N3 is connected to the comparator.

The integral circuit composed of the front-stage integrator N2 is a low-frequency square wave obtained by frequency division of the crystal oscillator. Its frequency is 16KHz. The integral capacitor CT1 in the integral circuit composed of N2 has a capacitance of 0.033uf. The values of RT2 and RT3 can be flexibly adjusted as needed. To fine-tune the horizontal potential of the output threshold triangle wave, in order to fine-tune the measured linearity of the circuit, so that the circuit can achieve the desired working accuracy.

As shown in Figure 4, the ultra-high-speed switching circuit 8 is composed of transistors V1, V2, field effect transistor V3 and peripheral circuits. The base of the transistor V1 is connected in parallel with the output end of the digital processing circuit 7 through a resistor R1 and a capacitor C1. The collector of V1 is connected to the power supply, the emitter of triode V1 is connected to the gate of field effect transistor V3 via resistor R2; the collector of triode V2 is connected to the gate of field effect transistor V3, and the emitter of triode V2 is connected to the power supply. The base of the transistor V2 is connected to the node between the capacitor C1 and the resistor R1 through the capacitor C3, and the source and gate of the field effect transistor V3 are the output terminals of the ultra-high-speed switching circuit 8.

When the input is high level, transistor V1 is cut off, and when the G-level voltage of JFET tube V3 is -15v, the switch is turned off. When the input is low. Transistor V1 is turned on. By properly allocating the resistance values of R2 and R3, the G-level voltage of JFET tube V3 can be around -2v, and the switch is turned on. The charge and discharge path during the turn-on process is composed of transistor V1 and capacitor C2, while the charge and discharge path during the turn-off process is composed of transistor V2. Usually the conduction time of the transistor is smaller than the off time. This feature can be used. When the input is high level, the transistor V2 is turned on first, and then the transistor V1 is turned off. This will make the G-level voltage of the JFET tube V3 be -15v. , because, even when the transistor V1 is not completely turned off, the conduction of the transistor V2 will immediately charge the G level of the JFET to -15v. The base capacitance C3 of the transistor V2 will generate an excitation to keep the transistor on until V1 is completely turned off. Similarly, when the input is low level, the base capacitor C1 of the transistor V1 will generate an excitation to turn on the transistor V1, and the capacitor C2 will immediately charge the JFET to turn on the JFET. By optimizing the parameters of each component, the switching rate of the ultra-high-speed switching circuit can be less than 5ns.

Working principle: The input current is connected to the input terminal of the main integrator 5, and the constant current source circuit 9 is also connected to the input terminal of the main integrator 1 circuit through the ultra-high-speed switch circuit 8. In this way, these two currents will cause the main integrator 1 circuit to Continuously integrate and reset to generate a periodic sawtooth wave integrated voltage. This integrated voltage is connected to the comparator 5 and compared with the threshold level, and then the integrated voltage is digitized to form a high and low pulse waveform. The output of the comparator 5 is connected to the digital processing circuit 7 input, the digital processing circuit 7 shapes the digitized pulse wave according to the frequency output by the shaping circuit, so that the pulse width and frequency of the pulse wave are synchronized to an integer multiple of the frequency output by the shaping circuit 6, and the pulse wave output by the digital processing circuit 7 Controls the on-off of the ultra-high-speed switch circuit 8, thereby realizing the disconnection and access of the constant current source circuit, and controls the integration and reset time of the main integrator 1. According to the principle of charge balance, the ratio of the integration and reset time of the sawtooth wave Proportional to the input current, and the standardized pulse duty cycle output by the digital processing circuit 7 is proportional to the ratio of the integral of the sawtooth wave and the reset time, so the output of the digital processing circuit 7 is proportional to the input circuit, and the output circuit is based on the pulse output by the digital processing circuit. The duty cycle generates an integer multiple of the frequency pulse number, so the number of pulses output by the output circuit is proportional to the input current, thereby achieving high-precision conversion of analog current to digital pulses.

Figure 5 shows the working waveform of the circuit. When the input current Iin is small, the main integrator 1 waveform works at the upper end of the threshold triangle wave, and the integration and reset process is completed within one cycle of the triangle wave. At this time, the reset pulse is small, corresponding to The output pulses are fewer. When the input current Iin is large, the main integrator 1 waveform works at the lower end of the threshold triangle wave, and the integration and reset processes are also completed within one cycle of the triangle wave. At this time, the reset pulse is larger and the corresponding output pulses are more. It can be seen that with the introduction of low-frequency triangular waveforms, the circuit integral reset always works at a lower switching frequency when inputting large and small currents. The operating frequency is the frequency of the threshold triangular wave level of 16KHz, which will greatly Reduce the overall error caused by the switching transition process and reduce the high-frequency error of the integrator. The output circuit can obtain the number of output pulses proportional to the width of the reset pulse by summing the 128KHz frequency standard signal generated by the crystal oscillator 2 with the reset pulse, thereby achieving high-precision conversion from current to frequency.

The above-described embodiments are only descriptions of preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, those of ordinary skill in the art may make various modifications to the technical solutions of the present invention. Deformations and improvements shall fall within the protection scope determined by the claims of the present invention.

Claims (4)

1. A current/frequency conversion circuit based on triangular wave modulation, characterized by: including a main integrator, a comparator, a digital processing circuit, a shaping circuit, an ultra-high-speed switching circuit, a constant current source circuit, an output circuit and a triangular wave generation circuit, The input terminal of the main integrator is the input current terminal, the output terminals of the main integrator and the triangular wave generating circuit are connected to the input terminal of the comparator, and the output terminal of the comparator is connected to one input terminal of the digital processing circuit. The two output terminals are respectively connected to the control terminal of the ultra-high-speed switching circuit and the input terminal of the output circuit. The input terminal of the ultra-high-speed switching circuit is connected to the output terminal of the constant current source circuit. The output terminal of the ultra-high-speed switching circuit is connected to the main integrator. The input end is connected, the output end of the shaping circuit is connected to the other input end of the digital processing circuit, the input end of the shaping circuit is connected to the output end of the triangular wave generating circuit; the triangular wave generating circuit includes a frequency division circuit, a threshold integration amplifier circuit and a crystal oscillator. The input end of the frequency circuit is connected to the input end of the shaping circuit via the crystal oscillator, the output end of the frequency dividing circuit is connected to the input and output of the threshold integration amplifier circuit, and the output end of the threshold integration amplifier circuit is connected to the input end of the comparator; the main integral The device includes a precision operational amplifier N1, an integrating capacitor Cf1, a triode VJ1 and a triode VJ2. The non-inverting input terminal of the precision operational amplifier N1 is grounded, and its inverting input terminal is used as the input current terminal through the resistor RJ1. The output terminal of the precision operational amplifier N1 is in turn The resistors RJ2 and RJ3 are connected to the input end of the comparator. The bases of the transistors VJ1 and VJ2 are connected at the node between the resistors RJ2 and RJ3. The collector of the transistor VJ1 is connected to the positive electrode of the power supply. The collector of the transistor VJ2 Connected to the negative pole of the power supply, the emitters of transistor VJ1 and transistor VJ2 are connected to the input end of the comparator and one end of the integrating capacitor Cf1 through resistors RJ4 and RJ5 respectively. The other end of the integrating capacitor Cf1 is connected to the inverting input end of the precision operational amplifier N1. ; Among them, transistor VJ1 is an N-type transistor, and transistor VJ2 is a P-type transistor. 2. The current/frequency conversion circuit based on triangular wave modulation according to claim 1, characterized in that: the threshold integral amplifier circuit includes an integrator N2 and a proportional operational amplifier N3, and the non-inverting input end of the integrator N2 is grounded. Its inverting input terminal is connected to the output terminal of the frequency division circuit through resistor RT1. The output terminal of integrator N2 is connected to the inverting input terminal of proportional operational amplifier N3 through resistor RT2. The non-inverting input terminal of proportional operational amplifier N3 is connected to ground. The proportional operation The output of amplifier N3 is connected to the comparator. 3. The current/frequency conversion circuit based on triangular wave modulation according to claim 1, characterized in that: the ultra-high-speed switching circuit is composed of transistors V1, V2, a field effect transistor V3 and a peripheral circuit, and the base of the transistor V1 is The pole is connected to the output end of the digital processing circuit through resistor R1 and capacitor C1 in parallel. The emitter of transistor V1 is connected to the power supply. The collector of transistor V1 is connected to the gate of field effect transistor V3 through resistor R2. The triode V2 collects The electrode is connected to the gate of the field effect transistor V3, its emitter is connected to the power supply, and its base is connected to the node between the capacitor C1 and the resistor R1 through the capacitor C3. The source and gate of the field effect transistor V3 are ultra-high-speed switches. The output end of the circuit; one end of the capacitor C2 is connected between the resistor R2 and the collector of the transistor V1, and the other end of the capacitor C2 is connected to the gate of the field effect transistor V3; among them, the transistor V1 is a P-type transistor, and the transistor V2 is an N-type transistor. . 4. A conversion method of a current/frequency conversion circuit based on triangular wave modulation, characterized in that it is used for the current/frequency conversion circuit based on triangular wave modulation as claimed in any one of claims 1 to 3, and it includes the following steps : (1) The constant current source circuit and the input current are continuously integrated and reset through the main integrator to generate a periodic sawtooth wave integrated voltage; (2) The integrated voltage is compared with the threshold level through a comparator and then the integrated voltage is digitized to form a high and low pulse waveform; (3) The pulse waveform is shaped by the digital processing circuit according to the output frequency of the shaping circuit, so that the pulse width and frequency of the pulse wave are synchronized to an integer multiple of the frequency output by the shaping circuit, and is simultaneously output by the digital processing circuit The pulse controls the on and off of the ultra-high-speed switching circuit, realizes the disconnection and access of the constant current source circuit, and controls the integration and reset time of the main integrator.