Voltage / frequency conversion circuit with temperature drift suppression function

Abstract

The invention discloses a voltage / frequency conversion circuit with a temperature drift suppression function. The invention comprises: a voltage / frequency conversion circuit for converting an input voltage signal into an output frequency signal proportional to the input voltage signal; the feedback circuit is used for converting the output frequency signal into an analog voltage signal and feeding the analog voltage signal back to the input end to form closed-loop control; and the temperature compensation circuit is used for converting the reference frequency signal into a reference feedback voltage by driving a reference feedback circuit which is completely symmetrical with the feedback circuit, and performing temperature drift compensation on the feedback signal by using the deviation between the voltage and a theoretical value. On-line temperature drift compensation can be achieved without a temperature sensor, the structure is symmetrical, response is rapid, and the device is suitable for being applied to a high-precision voltage / frequency conversion system.

Description

Technical Field

[0001] This invention belongs to the technical field of voltage / frequency conversion circuits, specifically a voltage / frequency conversion circuit with temperature drift suppression function. Background Technology

[0002] In precision measurement and metrology applications, optical isolation output is required through voltage / frequency conversion. Although existing voltage / frequency conversion chips can meet general conversion requirements, their noise and linearity are still insufficient to support high dynamic range or high-precision metrology applications.

[0003] In existing designs for improving the linearity of voltage / frequency conversion, charge balancing techniques maintain a balanced integrator output by precisely controlling the charging and discharging currents, thus improving linearity. However, this requires extremely high accuracy in constant current source matching; current source mismatch can introduce nonlinearity, and the nonlinearity error of the integrator can still affect conversion accuracy. Servo loop technology introduces closed-loop feedback based on the charge balancing method, improving system linearity by dynamically adjusting the internal parameters of the voltage / frequency converter. However, the servo loop itself is also affected by temperature changes; the temperature drift of its loop gain and key component characteristics can still cause linearity shifts under different temperature conditions.

[0004] In summary, the above methods can improve the linearity of voltage / frequency conversion circuits to a certain extent, but the system linearity is still affected by the feedback accuracy, and the thermal stability of its conversion coefficient is insufficient. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a voltage / frequency conversion circuit with temperature drift suppression functionality. This circuit improves the linearity of the voltage / frequency conversion circuit while suppressing temperature drift, comprising:

[0006] A voltage-to-frequency conversion circuit is used to convert an input voltage signal into an output frequency signal that is proportional to it.

[0007] A feedback circuit is used to convert the output frequency signal into an analog voltage signal and feed it back to the input terminal to form a closed-loop control.

[0008] The temperature compensation circuit, through driving a reference feedback circuit that is completely symmetrical with the feedback circuit, is used to convert the reference frequency signal into a reference feedback voltage, and to use the deviation between this voltage and the theoretical value to compensate for the temperature drift of the feedback signal.

[0009] Furthermore, the voltage / frequency conversion circuit includes:

[0010] A voltage-controlled current source is used to output a current proportional to the input voltage value to charge the integrator; a monostable trigger is used to output a control signal to control the analog switch; the analog switch is used to receive the control signal to short-circuit and discharge the integrating capacitor when the integrator output reaches the comparator threshold, and continue to charge the capacitor in the next cycle to form a periodic pulse.

[0011] Furthermore, the feedback circuit includes:

[0012] A pulse shaping circuit is used to convert the output frequency signal into a pulse signal with a fixed width and amplitude; a low-pass filter is used to convert the pulse signal into an analog signal; a first subtractor is used to subtract the temperature drift error from the analog signal and output a temperature drift compensated feedback signal.

[0013] Furthermore, the pulse shaping circuit outputs a pulse signal with a width smaller than the maximum frequency of the output range, and the amplitude and width are fixed to ensure that the average voltage of the pulse sequence is linearly related to the output frequency.

[0014] Furthermore, the temperature compensation circuit includes:

[0015] A frequency reference source is used to generate a stable fixed frequency signal; a reference feedback circuit is used to convert the fixed frequency signal into a reference feedback voltage; a second subtraction module is used to compare the reference feedback voltage with its theoretical value and calculate the difference, and then dynamically compensate the feedback voltage after obtaining the temperature drift error of the feedback circuit, so as to suppress the temperature drift of the feedback path.

[0016] Furthermore, the theoretical value of the reference feedback voltage is a preset fixed voltage generated by a reference circuit, which is used as the ideal output voltage reference for the reference feedback circuit.

[0017] Furthermore, the frequency reference source employs a temperature-compensated crystal oscillator.

[0018] In particular, the reference feedback circuit and the feedback circuit are completely symmetrical in structure, device parameters and wiring layout.

[0019] Furthermore, both the first subtractor module and the second subtractor module are implemented by differential amplifier circuits composed of operational amplifiers, which are used to accurately perform the difference calculation between the feedback voltage and the compensation voltage.

[0020] Based on the above technical solution, the present invention produces the following beneficial effects:

[0021] This invention introduces a feedback circuit to linearize the output relationship of the voltage / frequency conversion circuit, so that the overall linearity of the system is mainly determined by the performance of the feedback circuit.

[0022] This invention utilizes a temperature compensation circuit to correct temperature drift errors in the feedback path, achieving online temperature drift compensation without the need for a temperature sensor. It features a symmetrical structure, rapid response, and significantly improves the thermal stability of the system. This significantly reduces the sensitivity of system gain and zero-point offset to temperature changes, making it suitable for high-precision voltage / frequency conversion system applications.

[0023] This invention uses a temperature-compensated crystal oscillator as a frequency reference source, which has extremely high frequency stability and can output a reference frequency signal with minimal temperature drift, providing a reliable frequency reference for the temperature compensation path. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a voltage / frequency conversion circuit with temperature drift suppression function according to an embodiment of this application.

[0025] Figure 2 for Figure 1 The circuit structure diagram.

[0026] Figure 3 for Figure 2 The specific circuit component connection diagram.

[0027] Figure 4 The voltage values ​​of the voltage / frequency conversion circuit at different temperatures provided in the embodiments of this application are (temperature drift is not compensated).

[0028] Figure 5 The voltage values ​​of the voltage / frequency conversion circuit at different temperatures provided in the embodiments of this application are (temperature drift has been compensated). Detailed Implementation

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] like Figure 1As shown, traditional voltage / frequency conversion circuits suffer from insufficient linearity for high-precision measurements and are susceptible to temperature variations. This application provides a voltage / frequency conversion circuit with temperature drift suppression. A feedback circuit is added to the existing voltage / frequency conversion circuit. The output frequency signal of the voltage / frequency conversion circuit is converted into a pulse signal of fixed width and amplitude by a pulse shaping circuit. The pulse signal is then smoothed by a low-pass filter and proportionally fed back to the input to form a closed-loop control. The system's linearity is determined solely by the feedback accuracy. However, the timing capacitor and internal comparator of the pulse shaping circuit are susceptible to temperature variations, resulting in temperature drift. To suppress the temperature drift generated by the feedback circuit, this application further employs a fixed-frequency signal output from a frequency reference source to drive a reference feedback circuit that is structurally and parametrically symmetrical to the feedback circuit. By comparing the output of the reference feedback circuit with its theoretical value, the deviation caused by temperature changes in the feedback circuit can be obtained, and this deviation can be compensated for in the feedback circuit, thereby effectively suppressing the temperature drift of the feedback circuit.

[0031] Furthermore, the circuit in this embodiment includes:

[0032] A voltage-to-frequency conversion circuit is used to convert an input voltage signal into an output frequency signal that is proportional to it.

[0033] The feedback circuit is used to convert the frequency signal output by the voltage / frequency conversion circuit into an analog voltage signal and feed it back to the input terminal to form a closed-loop control.

[0034] The temperature compensation circuit is used to convert the reference clock signal into a reference feedback voltage signal through a reference feedback circuit whose structure is completely symmetrical with the feedback circuit, in order to compensate for the feedback signal (i.e., the temperature drift of the feedback circuit).

[0035] The following is combined Figure 2 The circuits described above will be described in detail below:

[0036] (1) Voltage / frequency conversion circuit, including voltage-controlled current source, integrator, comparator, monostable trigger and analog switch.

[0037] The voltage-controlled current source is based on the input voltage. The output current charges the integrator. When the integrator output reaches the comparator threshold, it triggers the monostable multivibrator to output an analog switch control signal to short-circuit and discharge the integrating capacitor. In the next cycle, it continues to charge the capacitor, forming a periodic pulse.

[0038] Specifically, the integrating capacitor charging current, charging time, and input voltage... This proportional relationship enables a linear conversion between voltage and frequency. Let the transconductance of the current source be... The integrator capacitor has a value of C, an initial voltage of 0, and a comparator voltage threshold of . Then the output frequency can be expressed as: .

[0039] (2) Feedback circuit, including pulse shaping circuit, low-pass filter and first subtractor.

[0040] The pulse shaping circuit converts the output frequency signal into a pulse signal with a fixed width and amplitude. The pulse signal is converted into an analog voltage signal by a low-pass filter. The analog voltage signal is then subtracted from the feedback voltage signal by a first subtractor to generate a temperature drift compensated feedback signal.

[0041] Furthermore, the pulse shaping circuit consists of a pulse generator and its peripheral resistor and capacitor circuits. Its timing capacitor and internal comparator delay are easily affected by temperature, which in turn affects the feedback accuracy and reduces the linearity of the system.

[0042] Based on this, in the embodiments of this application, the width of the output pulse signal of the pulse shaping circuit is set to be less than the maximum frequency of the output range, and the amplitude and width of the output pulse signal are fixed and do not change with the voltage / frequency output pulse frequency, so as to ensure that the average voltage of the pulse sequence is linearly related to the voltage / frequency output frequency.

[0043] Furthermore, by comparing the feedback voltage With the original input voltage The charging current of the driving voltage / frequency conversion circuit forms a closed-loop control, and the system linearity no longer depends on the voltage / frequency converter, but only on the pulse accuracy. Assuming the pulse generator output pulse amplitude is A and the width is d, calculate the feedback voltage: .

[0044] (3) Temperature compensation circuit, including frequency reference source, reference voltage source, reference feedback circuit and second subtractor;

[0045] A frequency reference source is used to generate a stable, fixed-frequency signal, which is converted into a reference feedback voltage by a reference feedback circuit. A second subtractor compares this reference feedback voltage with its theoretical value to obtain the error signal caused by temperature changes in the feedback circuit. Based on this error signal, the main feedback voltage is dynamically compensated, thereby suppressing temperature drift in the feedback path.

[0046] The theoretical value of the reference feedback voltage is a preset fixed voltage generated by a reference circuit and used as the ideal output voltage reference for the reference feedback circuit.

[0047] Furthermore, the reference feedback circuit is completely symmetrical to the feedback circuit in terms of structure, device parameters, and wiring layout. Therefore, the influence of temperature changes on the pulse amplitude and pulse width of the feedback circuit can be synchronously presented and accurately extracted in the reference path, effectively offsetting the temperature drift of the feedback circuit, thereby ensuring that the system has a consistent temperature response and stable feedback accuracy across the entire temperature range.

[0048] Specifically, both the first subtractor and the second subtractor are implemented using differential amplifier circuits composed of operational amplifiers, which are used to accurately perform the difference calculation between the feedback voltage and the compensation voltage.

[0049] In this embodiment, the frequency reference source is a temperature-compensated crystal oscillator, which has extremely high frequency stability and can output a reference frequency signal with minimal temperature drift, providing a reliable frequency reference for the temperature compensation path.

[0050] like Figure 3 As shown, based on the same concept as the above embodiments, this test example provides a specific circuit connection diagram, specifically as follows:

[0051] (1) The voltage / frequency conversion circuit includes:

[0052] The voltage-controlled current source consists of operational amplifiers G1 and G2 and resistors R1 to R5; its inverting input is coupled to the input voltage Vin, its non-inverting input is coupled to the output of the feedback circuit, and its output is coupled to the input of the integrator.

[0053] The integrator consists of operational amplifier G3 and capacitor C1, with capacitor C1 coupled to both the inverting input and output of the operational amplifier. The integrator output is coupled to the inverting input of comparator U1, and the threshold voltage V... th The comparator output is coupled to the non-inverting input of the comparator, and the comparator output is coupled to the inputs of the monostable multivibrator and the optocoupler.

[0054] The output of the monostable multivibrator is coupled to the control pin of the analog switch, and the two ends of the analog switch are coupled to the two ends of the capacitor C1 to control the charging and discharging of the integrator capacitor C1.

[0055] In this test case, the voltage-controlled current source uses an enhanced Howland current source circuit, and its resistance satisfies... , At this time, the output current is independent of the load and is only controlled by the input voltage. The output current is: ,in, .

[0056] By charging the integrator capacitor with a current source, the integration result depends only on the linear integral of the current, and the integrator output is: .

[0057] The integrator output is compared with a threshold voltage by a comparator. When the integrator output reaches the comparator threshold, an analog switch is triggered to short-circuit and discharge the integrating capacitor. The capacitor continues to charge in the next cycle, forming a periodic pulse. In this test example, the comparator used is the LT1719, which features a low propagation delay of 4.5ns and provides a peak output current of 50mA, allowing direct driving of subsequent optocouplers. The output of the voltage / frequency conversion circuit without feedback is as follows: ,in, This is the comparator threshold voltage.

[0058] (2) The feedback circuit includes:

[0059] The input of the pulse shaping circuit is coupled to the output of the comparator, and the output is coupled to the input of a third-order low-pass filter consisting of operational amplifier G4, resistors R6~R8 and capacitors C2~C4.

[0060] The low-pass filter output is connected to operational amplifier G5 and resistors R9~R 12 The first subtractor is coupled to the non-inverting input, and its output is coupled to the inverting input of the voltage-controlled current source.

[0061] Furthermore, the feedback circuit operates as follows: the output frequency signal is converted into a pulse signal with fixed amplitude and width by a pulse shaping circuit, and the pulse is smoothed by a low-pass filter to output an analog voltage signal. This analog voltage signal is then subtracted from the temperature drift compensation voltage by a first subtractor and fed back to the input, forming a closed-loop control. Based on this, the system linearity no longer depends on the voltage / frequency converter, but is mainly determined by the pulse accuracy in the feedback loop.

[0062] In this test case, a 74LVC123 monostable multivibrator is used as the pulse generator. Its pulse width d is determined by an external RC network, and the pulse amplitude A is determined by the supply voltage. The feedback voltage of the feedback circuit is: .

[0063] Since the pulse amplitude and pulse width output by the feedback circuit remain constant, and its average value after low-pass filtering is strictly linearly related to the frequency, the output of the voltage / frequency conversion circuit after adding feedback is: ,in, .

[0064] Therefore, the linearity of the voltage / frequency conversion circuit is mainly determined by the feedback circuit.

[0065] (3) The temperature compensation circuit includes:

[0066] The frequency reference source output is coupled to the pulse shaping circuit input, and the pulse generator output is coupled to the input of the operational amplifier G6 and resistor R. 13 ~R 15It is coupled to the input of a third-order low-pass filter composed of capacitors C5 to C7.

[0067] The low-pass filter output is connected to the operational amplifier G7 and resistor R. 16 ~R 19 The second subtractor is coupled at the non-inverting input, with a reference voltage V. ref It is coupled to the inverting input of the second subtractor.

[0068] The output of the second subtractor is coupled to the inverting input of the first subtractor.

[0069] In this test case, a high-precision temperature-compensated crystal oscillator with a frequency of 0.1 ppm and its oscillator circuit were used as the frequency reference source to output a reference frequency signal with a fixed frequency. A reference feedback circuit that is completely symmetrical to the drive and feedback circuits. The reference feedback circuit compares the second subtractor with a reference voltage. The deviation reflects the temperature drift of the feedback circuit and is output to the input of the second subtractor in the feedback circuit. The temperature compensation voltage is: .

[0070] The transfer function of the system with temperature compensation is obtained as follows:

[0071]

[0072] in, For system gain, when At this time, the gain K is determined only by the feedback coefficient Ad; This is the temperature-compensated frequency. Under standard temperature... When the feedback coefficient Ad drifts due to temperature, The system undergoes corresponding frequency compensation, significantly reducing the temperature drift of the feedback coefficient Ad and maintaining stability of the linear relationship across the entire operating temperature range. Therefore, the voltage / frequency conversion circuit exhibits extremely high linearity and thermal stability.

[0073] At different temperatures, the feedback signal of the voltage / frequency conversion circuit without temperature compensation is as follows: Figure 4 As shown in the figure, the horizontal axis represents time, and the vertical axis represents voltage amplitude. It can be observed that the components in the feedback circuit are affected by temperature, causing a shift in the feedback voltage, which in turn affects the output frequency of the voltage / frequency conversion circuit.

[0074] The feedback signal of the voltage / frequency conversion circuit with added temperature compensation is as follows: Figure 5 As shown in the figure, the horizontal axis represents time, and the vertical axis represents voltage amplitude. It can be observed that the feedback voltage value remains essentially consistent across different temperatures after compensation, thus effectively suppressing the temperature drift of the voltage / frequency conversion circuit.

[0075] By configuring the parameters as described above, the temperature drift of the circuit is effectively suppressed within the frequency output range. The compensated system output frequency maintains a high degree of linearity with the input voltage, and the system zero-point offset is completely eliminated or limited to a very small range, thereby achieving a voltage / frequency conversion output with high linearity and high thermal stability.

[0076] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A voltage / frequency conversion circuit with temperature drift suppression function, characterized in that, include: The feedback circuit is used to convert the frequency signal output by the voltage / frequency conversion circuit into an analog voltage signal and feed it back to the input terminal to form a closed-loop control. The temperature compensation circuit is used to convert the reference frequency signal into a reference feedback voltage and use the deviation between this voltage and the theoretical value to compensate for the temperature drift of the feedback signal.

2. The voltage / frequency conversion circuit with temperature drift suppression function according to claim 1, characterized in that, The voltage / frequency conversion circuit includes: A voltage-controlled current source is used to output a current proportional to the input voltage value to charge the integrator; A monostable multivibrator is used to output a control signal to control an analog switch; An analog switch is used to receive the control signal when the integrator output reaches the comparator threshold, short-circuit and discharge the integrating capacitor, and continue to charge the capacitor in the next cycle to form a periodic pulse.

3. A voltage / frequency conversion circuit with temperature drift suppression function according to claim 1, characterized in that, The feedback circuit includes: A pulse shaping circuit is used to convert the output frequency signal into a pulse signal with a fixed width and amplitude. A low-pass filter is used to convert the pulse signal into an analog signal; The first subtractor is used to subtract the temperature drift error from the analog signal and output the temperature drift compensated feedback signal.

4. A voltage / frequency conversion circuit with temperature drift suppression function according to claim 3, characterized in that, The pulse shaping circuit outputs a pulse signal with a width smaller than the maximum frequency of the output range, and the amplitude and width are fixed to ensure that the average voltage of the pulse sequence is linearly related to the output frequency.

5. A voltage / frequency conversion circuit with temperature drift suppression function according to claim 3 or 4, characterized in that, The temperature compensation circuit includes: A frequency reference source is used to generate a stable, fixed-frequency signal. A reference feedback circuit is used to convert the fixed frequency signal into a reference feedback voltage; The second subtraction module is used to compare the reference feedback voltage with its theoretical value and calculate the difference. After obtaining the temperature drift error of the feedback circuit, the feedback voltage is dynamically compensated to suppress the temperature drift of the feedback path.

6. A voltage / frequency conversion circuit with temperature drift suppression function according to claim 5, characterized in that, The theoretical value of the reference feedback voltage is a preset fixed voltage generated by a reference circuit and used as the ideal output voltage reference for the reference feedback circuit.

7. A voltage / frequency conversion circuit with temperature drift suppression function according to claim 6, characterized in that, The frequency reference source is a temperature-compensated crystal oscillator.

8. A voltage / frequency conversion circuit with temperature drift suppression function according to claim 6 or 7, characterized in that, The reference feedback circuit and the feedback circuit are completely symmetrical in structure, device parameters and wiring layout.

9. A voltage / frequency conversion circuit with temperature drift suppression function according to claim 8, characterized in that, Both the first subtractor module and the second subtractor module are implemented by differential amplifier circuits composed of operational amplifiers, which are used to accurately perform the difference calculation between the feedback voltage and the compensation voltage.

Images