A high-precision current / frequency conversion circuit

Abstract

The present invention discloses a high-precision current-to-frequency conversion circuit, comprising an integration circuit, a voltage threshold detection circuit A, a voltage threshold detection circuit B, a voltage reference source A, a voltage reference source B, a clock and reset circuit, a main control circuit, an analog switch, a constant current source A, a constant current source B, an A / D conversion circuit, and a temperature acquisition circuit. By adding the A / D conversion circuit and the temperature acquisition circuit, the present invention enables real-time detection of the integration circuit's output voltage and operating ambient temperature. Through algorithmic processing in a compensation processing unit, accurate real-time compensation of the output pulses is achieved, improving the nonlinearity performance of the current-to-frequency conversion circuit to less than 50 ppm over the full input-output temperature range (-35°C to 65°C).

Description

Technical Field

[0001] The present invention belongs to analog-digital hybrid circuit technology, and in particular relates to a high-precision current / frequency conversion circuit. Technical Background

[0002] Improving the accuracy and nonlinearity of inertial sensing units is the key to improving the inertial navigation accuracy of vehicles. Usually, high-precision inertial sensing systems require accelerometer accuracy of 10 -5 g, so the accuracy of the digital-to-analog converter needs to reach 10 -6 g is required to ensure system accuracy. Common detection methods for the current signal output by quartz accelerometers include A / D conversion and I / F conversion. The A / D conversion method converts the current signal into a voltage signal, then uses an A / D converter to measure the voltage signal and infer the input current signal. To meet high-precision detection requirements, a high-precision Σ-Δ A / D converter with 24 bits or more is typically required. The I / F conversion scheme uses the principle of capacitor charge balance to control bidirectional integration of the integrator capacitor. Unlike the sampling detection method of the A / D converter, the I / F converter continuously detects the input signal, eliminating the risk of original information loss. Furthermore, through continuous integration, it can smooth out noise signals to a certain extent. The I / F conversion scheme offers improved interference immunity and is therefore widely used in accelerometer signal acquisition and conversion.

[0003] Since the performance parameters of electronic components are easily affected by the operating environment temperature and change (commonly known as temperature drift), this factor will have a significant impact on the input and output nonlinearity indicators of the current / frequency conversion circuit, reducing the circuit's environmental adaptability. Summary of the Invention

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the existing technology and provide a high-precision current / frequency conversion circuit that can achieve synchronous pulse output compensation, reduce response delay, and improve the nonlinearity of input current and output frequency in the full temperature range.

[0005] The technical solution of the present invention is:

[0006] A high-precision current / frequency conversion circuit, comprising: an integration circuit, a voltage threshold detection circuit A, a voltage threshold detection circuit B, a voltage reference source A, a voltage reference source B, a clock and reset circuit, a main control circuit, an analog switch, a constant current source A, a constant current source B, an A / D conversion circuit, and a temperature acquisition circuit;

[0007] The integrator circuit receives the external input current I in The balance current of the analog switch feedback, the integration circuit U1 to the input current Iin The difference between the input current and the balance current is integrated, and the output integral voltage Vout(t) is given to the voltage threshold detection circuit A, the voltage threshold detection circuit B and the A / D conversion circuit respectively; the input current I in Positive current input or negative current input;

[0008] Under positive current input, the voltage threshold detection circuit A receives the first reference voltage output by the voltage reference source A, compares the output voltage of the integration circuit under positive current input with the first reference voltage, obtains a first square wave signal, and outputs it to the main control circuit;

[0009] Under negative current input, the voltage threshold detection circuit B receives the second reference voltage output by the voltage reference source B, compares the output voltage of the integration circuit under negative input current with the second reference voltage, obtains a second square wave signal, and outputs it to the main control circuit;

[0010] The temperature acquisition circuit collects the ambient temperature and outputs the temperature signal to the main control circuit;

[0011] The A / D conversion circuit receives the integrated voltage, performs digital processing on it, and outputs it to the main control circuit;

[0012] The clock and reset circuit is used to output clock signals and reset signals to the main control circuit;

[0013] The main control circuit receives the square wave signal output by the voltage threshold detection circuit A or the voltage threshold detection circuit B, receives the digital signal corresponding to the integrated voltage output by the A / D conversion circuit and the temperature signal output by the temperature acquisition circuit; compensates the frequency in the square wave signal to obtain the real-time pulse compensation amount; and obtains the input current I according to the digital signal corresponding to the integrated voltage, the temperature signal and the real-time pulse compensation amount using the clock signal. in The corresponding ideal pulse signal is outputted externally; the square wave signal includes: a first square wave signal and a second square wave signal;

[0014] The analog switch is controlled by the main control circuit and selects constant current source A or constant current source B to output a balanced current and feed it back to the integration circuit;

[0015] The reset signal is used to control the main control circuit to output an ideal pulse signal after the current / frequency conversion circuit is powered on and starts working stably.

[0016] Preferably, the clock signal is a square wave signal, and the reset signal is a single-shot enable signal.

[0017] Preferably, the main control circuit includes: a frequency extraction unit;

[0018] The frequency extraction unit uses the characteristic quantity of the square wave signal to output an enable signal to the analog switch; the enable signal is used to control the analog switch to output a negative constant current as a balancing current to be fed back to the integration circuit under positive current input; and to control the analog switch to output a positive constant current as a balancing current to be fed back to the integration circuit under negative current input.

[0019] Preferably, the current / frequency conversion circuit further comprises: a constant current source B;

[0020] The negative constant current for controlling the output of the analog switch is provided by constant current source B.

[0021] Preferably, the current / frequency conversion circuit further comprises: a constant current source A;

[0022] The positive constant current that controls the analog switch output is provided by constant current source A.

[0023] Preferably, the main control circuit further comprises: a positive and negative pulse output unit and a compensation control processing unit;

[0024] The frequency extraction unit uses the square wave signal to obtain the actual output pulse quantity n before compensation. f , and output to the positive and negative pulse output unit and the compensation control processing unit;

[0025] The compensation control processing unit receives the digital signal corresponding to the integrated voltage output by the A / D conversion circuit and the temperature signal, as well as the actual output pulse quantity n before compensation output by the frequency extraction unit. f ; According to the digital signal and temperature signal corresponding to the integrated voltage, the compensation enable signal Enble is generated and output to the positive and negative pulse output unit; and according to the actual output pulse quantity n before compensation f Generate real-time pulse compensation ΔN fout (t), output to the positive and negative pulse output unit;

[0026] The positive and negative pulse output unit receives the real-time pulse compensation value ΔN output by the compensation control processing unit fout (t) and compensation enable signal Enble, the actual output pulse quantity n before compensation output by the receiving frequency extraction unit f ; Use the compensation enable signal Enble to set the real-time pulse compensation value ΔN fout (t) Actual output pulse quantity n before compensation synchronously superimposed on the output of the frequency extraction unit f , the input current I is obtained in The corresponding ideal pulse signal is output.

[0027] Preferably, the reset signal and the clock signal are output to the frequency extraction unit, the positive and negative pulse output unit and the compensation control processing unit respectively.

[0028] Preferably, the compensation control processing unit generates a real-time pulse compensation amount ΔN fout (t), specifically:

[0029] ΔN fout (t) = N fout (t)-N f

[0030]

[0031] N fout (t)=λ·i(t)+ν0

[0032] Among them, [n f1 … n fm ] T The actual output pulse quantity of the frequency extraction unit, K1~K m is the discrete scaling factor; b1~b m is the compensated vertical intercept of the fitting curve; λ and ν0 are the calibration coefficients of the ideal curve, and λ is greater than K1~K m The maximum value, ν0 is greater than b1~b m i(t) is the real-time current value estimated by the compensation control processing unit using the digital signal corresponding to the integrated voltage output by the A / D conversion circuit; I in is the input current value.

[0033] The advantages of the present invention compared with the prior art are:

[0034] The present invention realizes real-time detection of the output voltage of the integration circuit and the working environment temperature by adding an A / D conversion circuit and a temperature acquisition circuit. Through the algorithm processing of the compensation processing unit, real-time and accurate compensation of the output pulse is achieved, and the nonlinear performance index of the current / frequency conversion circuit within the input-output full temperature range (-35°C to 65°C) is improved to within 50ppm. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the structural block diagram of the high-precision current / frequency conversion circuit;

[0036] Figure 2 This is the control waveform timing diagram of the current / frequency conversion circuit;

[0037] Figure 3 This is a schematic diagram of the principle of the pulse compensation method. DETAILED DESCRIPTION

[0038] The present invention provides a high-precision current / frequency conversion circuit, which can improve the output accuracy of the current-frequency conversion circuit. Figure 1As shown, it includes: an integration circuit, a voltage threshold detection circuit A, a voltage threshold detection circuit B, a voltage reference source A, a voltage reference source B, a clock and reset circuit, a main control circuit, an analog switch, a constant current source A, a constant current source B, an A / D conversion circuit and a temperature acquisition circuit.

[0039] The integrator circuit receives the external input current I in The balance current of the analog switch feedback, the integration circuit U1 to the input current I in The difference between the input current and the balance current is integrated, and the output integral voltage Vout(t) is given to the voltage threshold detection circuit A, the voltage threshold detection circuit B and the A / D conversion circuit respectively; the input current I in Positive current input or negative current input;

[0040] Under positive current input, the voltage threshold detection circuit A receives the first reference voltage output by the voltage reference source A, compares the output voltage of the integration circuit under positive current input with the first reference voltage, obtains a first square wave signal, and outputs it to the main control circuit;

[0041] Under negative current input, the voltage threshold detection circuit B receives the second reference voltage output by the voltage reference source B, compares the output voltage of the integration circuit under the negative input current with the second reference voltage, obtains a second square wave signal, and outputs it to the main control circuit; the first reference voltage output by the voltage reference source A and the second reference voltage output by the voltage reference source B are not equal.

[0042] The temperature acquisition circuit collects the ambient temperature and outputs the temperature signal to the main control circuit;

[0043] The A / D conversion circuit receives the integrated voltage, performs digital processing on it, and outputs it to the main control circuit;

[0044] The clock and reset circuit is used to output clock signals and reset signals to the main control circuit; the clock signal is a square wave signal, and the reset signal is a single-trigger enable signal.

[0045] The main control circuit receives the square wave signal output by the voltage threshold detection circuit A or the voltage threshold detection circuit B, the square wave signal including: a first square wave signal and a second square wave signal; receives the digital signal corresponding to the integrated voltage output by the A / D conversion circuit and the temperature signal output by the temperature acquisition circuit; compensates the frequency in the square wave signal to obtain a real-time pulse compensation amount; obtains the input current I according to the digital signal corresponding to the integrated voltage, the temperature signal and the real-time pulse compensation amount using the clock signal. in The corresponding ideal pulse signal is outputted externally;

[0046] The analog switch is controlled by the main control circuit and selects constant current source A or constant current source B to output a balanced current and feed it back to the integration circuit;

[0047] The reset signal is used to control the main control circuit to output an ideal pulse signal after the current / frequency conversion circuit is powered on and starts working stably.

[0048] The main control circuit includes: a frequency extraction unit;

[0049] The frequency extraction unit uses the characteristic quantity of the square wave signal to output an enable signal to the analog switch; the enable signal is used to control the analog switch to output a negative constant current (provided by constant current source B) as a balancing current feedback to the integration circuit under positive current input; and to control the analog switch to output a positive constant current (provided by constant current source A) as a balancing current feedback to the integration circuit under negative current input.

[0050] The main control circuit also includes: a positive and negative pulse output unit and a compensation control processing unit;

[0051] The frequency extraction unit uses the square wave signal to obtain the actual output pulse quantity n before compensation. f , and output to the positive and negative pulse output unit and the compensation control processing unit;

[0052] The reset signal and the clock signal are output to the frequency extraction unit, the positive and negative pulse output unit and the compensation control processing unit respectively.

[0053] The compensation control processing unit receives the digital signal corresponding to the integrated voltage output by the A / D conversion circuit and the temperature signal, as well as the actual output pulse quantity n before compensation output by the frequency extraction unit. f ; According to the digital signal and temperature signal corresponding to the integrated voltage, the compensation enable signal Enble is generated and output to the positive and negative pulse output unit; and according to the actual output pulse quantity n before compensation f Generate real-time pulse compensation ΔN fout (t), output to the positive and negative pulse output unit;

[0054] The positive and negative pulse output unit receives the real-time pulse compensation value ΔN output by the compensation control processing unit fout (t) and compensation enable signal Enble, the actual output pulse quantity n before compensation output by the receiving frequency extraction unit f ; Use the compensation enable signal Enble to set the real-time pulse compensation value ΔN fout (t) Actual output pulse quantity n before compensation synchronously superimposed on the output of the frequency extraction unit f , the input current I is obtained in The corresponding ideal pulse signal is output.

[0055] The main control circuit is composed of any integrated IC chip with logic and timing control functions, such as FPGA, CPLD, DSP, ARM-based microprocessor, etc. The main control circuit uses the compensation control processing unit implemented by the internal program to complete the judgment and calculation of the output voltage data of the integration circuit collected by the A / D converter and the temperature data obtained by the temperature sensor to obtain the output pulse compensation result. The positive and negative pulse output unit inside the main control circuit is a functional module implemented by the program. Its function is to obtain the output result ΔN of the compensation control processing unit. fout (t) Realize compensation for the output pulse quantity.

[0056] The compensation control processing unit generates the real-time pulse compensation amount ΔN fout (t), specifically:

[0057] ΔN fout (t) = N fout (t)-N f

[0058]

[0059] N fout (t)=λ·i(t)+ν0

[0060] Among them, [n f1 … n fm ] T The actual output pulse quantity of the frequency extraction unit, K1~K m is the discrete scaling factor; b1~b m is the compensated vertical intercept of the fitting curve; λ and ν0 are the calibration coefficients of the ideal curve, and λ is greater than K1~K m The maximum value, ν0 is greater than b1~b m i(t) is the real-time current value estimated by the compensation control processing unit using the digital signal corresponding to the integrated voltage output by the A / D conversion circuit; I in is the input current value.

[0061] The integration circuit integrates the input current; the main control circuit controls the access status of constant current source A and constant current source B through analog switches, thereby achieving dynamic balance control of the charge stored in the integration capacitor; the clock and reset circuits provide clock and complex signals to the main control circuit; the power reference source A and the voltage reference source B provide corresponding voltage references for the voltage threshold detection circuit A and the voltage threshold detection circuit B, respectively, providing state judgment level signals for the control of the main control circuit; the present invention realizes real-time detection of the output voltage of the integration circuit and the working environment temperature by adding an A / D conversion circuit and a temperature acquisition circuit. Through the algorithm processing of the compensation processing unit, it realizes real-time and accurate compensation of the output pulse, and improves the nonlinear performance index of the current / frequency conversion circuit within the full input-output temperature range (-35°C to 65°C) to within 50ppm. In the system, the ratio of the output pulse quantity per unit time to the input current is usually called the scaling factor K. By discretizing the input current and output pulse quantity curves, multiple sets of K coefficients can be obtained. By calculating the stability of the K coefficients, the nonlinear index of the input current and output frequency can be obtained.

[0062] The specific steps for output pulse compensation are as follows:

[0063] (1) Step 1:

[0064] The input and output data of the current / frequency conversion circuit are fitted using the least squares method at a constant temperature. The principle can be found in Figure 3 , where the solid line represents the actual measured data (the current output by the quartz accelerometer). After fitting, a multi-segment function curve can be obtained, and the fitting result can be represented by the function matrix shown in formula (1).

[0065]

[0066] Among them, n f =[n f1 … n fm ] T is the actual output pulse quantity obtained by the frequency extraction unit after passing through the sampling window (determined by the first square wave signal or the second square wave signal); K1~K m is the fitting coefficient of the multi-segment curve, that is, the discrete scaling factor; b1~b m is the compensated vertical intercept of the fitting curve.

[0067] (2) Step 2:

[0068] The ideal current-pulse quantity function relationship after setting the fitting is shown in formula (2).

[0069] N fout (t)=λ·i(t)+ν0 (2)

[0070] Among them, λ and ν0 are the calibration coefficients of the ideal curve, λ is greater than K1~K m The maximum value, ν0 is greater than b1~b m At the same input current level, the ideal fitting curve is always higher than the actual fitting curve, such as Figure 3 shown.

[0071] (3) Step 3:

[0072] The A / D acquisition module collects the voltage Vout(t) of the triangular wave output by the integration circuit and converts it into a digital signal and sends it to the compensation control processing unit. The compensation control processing unit uses the digital signal corresponding to the output voltage Vout(t) of the integration circuit to detect the voltage value characteristics of the specific level of the triangular wave, preliminarily estimate the input current range, and obtain the estimated real-time current value i(t); the real-time current value i(t) estimated by the A / D conversion circuit is substituted into formula (2) and the difference is obtained to obtain the real-time pulse compensation amount ΔN fout (t).

[0073] ΔN fout (t) = N fout (t)-N f =[λ·i(t)+ν0)]-[K n ×i(t)+b n ]n∈[1,m]

[0074] (4) Step 4:

[0075] The compensation control processing unit converts the real-time pulse compensation value ΔN obtained in the previous step into fout (t) is input to the positive and negative pulse output unit, and the clock signal and compensation amount are used to generate an ideal pulse signal to be output to the outside. The specific implementation method is to adjust the pulse through the internally generated compensation enable signal Enble. The adjustment method is as follows Figure 2 As shown. in is the actual input current received by the integration circuit, Vout(t) is the output voltage value of the integration circuit, and the Enable signal is the compensation enable signal automatically generated by the positive and negative pulse output unit according to the compensation amount. This signal generates a compensation pulse ΔN internally. fout (t) and the actual output pulse quantity n before compensation f Adjust to the pulse N after accurate compensation fout (t), complete the compensation control of the output pulse of the current-frequency conversion circuit. N fout (t) is Fout+ or Fout-.

[0076] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention are within the scope of protection of the technical solutions of the present invention. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0077] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A high-precision current / frequency conversion circuit, characterized in that: include: Integration circuit, voltage threshold detection circuit A, voltage threshold detection circuit B, voltage reference source A, voltage reference source B, clock and reset circuit, main control circuit, analog switch, constant current source A, constant current source B, A / D conversion circuit and temperature acquisition circuit; The integrator circuit receives the external input current I in The balance current of the analog switch feedback, the integration circuit U1 to the input current I in The difference between the current and the balance current is integrated, and the output integrated voltage Vout(t) is given to the voltage threshold detection circuit A, the voltage threshold detection circuit B and the A / D conversion circuit respectively; Input current I in Positive current input or negative current input; Under positive current input, the voltage threshold detection circuit A receives the first reference voltage output by the voltage reference source A, compares the output voltage of the integration circuit under positive current input with the first reference voltage, obtains a first square wave signal, and outputs it to the main control circuit; Under negative current input, the voltage threshold detection circuit B receives the second reference voltage output by the voltage reference source B, compares the output voltage of the integration circuit under negative input current with the second reference voltage, obtains a second square wave signal, and outputs it to the main control circuit; The temperature acquisition circuit collects the ambient temperature and outputs the temperature signal to the main control circuit; The A / D conversion circuit receives the integrated voltage, performs digital processing on it, and outputs it to the main control circuit; The clock and reset circuit is used to output clock signals and reset signals to the main control circuit; The main control circuit receives the square wave signal output by the voltage threshold detection circuit A or the voltage threshold detection circuit B, receives the digital signal corresponding to the integrated voltage output by the A / D conversion circuit and the temperature signal output by the temperature acquisition circuit; compensates the frequency in the square wave signal to obtain the real-time pulse compensation amount; and obtains the input current I according to the digital signal corresponding to the integrated voltage, the temperature signal and the real-time pulse compensation amount using the clock signal. in The corresponding ideal pulse signal is outputted externally; The square wave signal includes: a first square wave signal and a second square wave signal; The analog switch is controlled by the main control circuit and selects constant current source A or constant current source B to output a balanced current which is fed back to the integration circuit; The reset signal is used to control the main control circuit to output an ideal pulse signal after the current / frequency conversion circuit is powered on and starts working stably; The main control circuit also includes: a positive and negative pulse output unit and a compensation control processing unit; The frequency extraction unit uses the square wave signal to obtain the actual output pulse quantity n before compensation. f , and output to the positive and negative pulse output unit and the compensation control processing unit; The compensation control processing unit receives the digital signal corresponding to the integrated voltage output by the A / D conversion circuit and the temperature signal, as well as the actual output pulse quantity n before compensation output by the frequency extraction unit. f ; According to the digital signal and temperature signal corresponding to the integrated voltage, the compensation enable signal Enble is generated and output to the positive and negative pulse output unit; and according to the actual output pulse quantity n before compensation f Generate real-time pulse compensation ΔN fout (t), output to the positive and negative pulse output unit; The positive and negative pulse output unit receives the real-time pulse compensation value ΔN output by the compensation control processing unit fout (t) and compensation enable signal Enble, the actual output pulse quantity n before compensation output by the receiving frequency extraction unit f ; Use the compensation enable signal Enble to set the real-time pulse compensation value ΔN fout (t) Actual output pulse quantity n before compensation synchronously superimposed on the output of the frequency extraction unit f , the input current I is obtained in The corresponding ideal pulse signal is output.

2. A high-precision current / frequency conversion circuit according to claim 1, characterized in that: The clock signal is a square wave signal, and the reset signal is a single-shot enable signal.

3. The high-precision current / frequency conversion circuit according to claim 1, characterized in that: The main control circuit includes: a frequency extraction unit; The frequency extraction unit uses the characteristic quantity of the square wave signal to output an enable signal to the analog switch; the enable signal is used to control the analog switch to output a negative constant current as a balancing current to be fed back to the integration circuit under positive current input; and to control the analog switch to output a positive constant current as a balancing current to be fed back to the integration circuit under negative current input.

4. The high-precision current / frequency conversion circuit according to claim 3, characterized in that: The current / frequency conversion circuit further includes: a constant current source B; The negative constant current for controlling the output of the analog switch is provided by constant current source B.

5. The high-precision current / frequency conversion circuit according to claim 4, characterized in that: The current / frequency conversion circuit further includes: a constant current source A; The positive constant current that controls the analog switch output is provided by constant current source A.

6. A high-precision current / frequency conversion circuit according to any one of claims 3 to 5, characterized in that: The reset signal and the clock signal are output to the frequency extraction unit, the positive and negative pulse output unit and the compensation control processing unit respectively.

7. The high-precision current / frequency conversion circuit according to claim 5, characterized in that: The compensation control processing unit generates the real-time pulse compensation amount ΔN fout (t), specifically: ΔN fout (t)=N fout (t)-N f N fout (t)=λ·i(t)+ν0 Among them, [n f1 ...n fm ] T The actual output pulse quantity of the frequency extraction unit, K1~K m is the discrete scaling factor; b1~b m is the compensated vertical intercept of the fitting curve; λ and ν0 are the calibration coefficients of the ideal curve, and λ is greater than K1~K m The maximum value, ν0 is greater than b1~b m i(t) is the real-time current value estimated by the compensation control processing unit using the digital signal corresponding to the integrated voltage output by the A / D conversion circuit; I in is the input current value.

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