An integration unit structure and current-frequency conversion circuit

Abstract

The present invention provides an integration unit structure and a current frequency conversion circuit, wherein the input current I in The resistor R1 and one end of the filter capacitor C1 are connected respectively, and the other end of the resistor R1 is connected respectively to the inverting input end of the first-stage operational amplifier U1, one end of the compensation capacitor C3 and one end of the integration capacitor C2; the other end of the filter capacitor C1 is connected respectively to the non-inverting input end of the first-stage operational amplifier U1 and the other end of the compensation capacitor C3; the output end of the first-stage operational amplifier U1 is connected to the non-inverting input end of the second-stage operational amplifier U2, and the output end of the second-stage operational amplifier U2 is connected respectively to one end of the compensation resistor R2 and the inverting input end of the second-stage operational amplifier U2; the other end of the integration capacitor C2 is connected to the other end of the compensation resistor R2; the positive power supply ends of the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are both connected to the voltage Vcc; the negative power supply ends of the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are both grounded and connected to the other end of the filter capacitor C1.

Description

Technical Field

[0001] The present invention belongs to the technical field of current-frequency conversion, and in particular to an integration unit structure and a current-frequency conversion circuit. Background Art

[0002] The current-frequency conversion circuit belongs to the analog-to-digital converter category. It is a precision signal processing circuit that can convert analog quantities into pulses proportional to them. In the development and production of aviation and aerospace models, it is widely used in A / D conversion of analog quantities output by sensors to achieve high-precision control.

[0003] The integration network is a key element in current-to-frequency conversion circuits, encompassing both the input and feedback terminals of the system. Traditional current-to-frequency conversion circuits employ a single op amp integration structure. As the scale factor of current-to-frequency conversion circuits increases, the high-frequency components of the overall circuit loop increase. Even with a high-speed op amp that meets zero-bit requirements, the integration network mismatches the overall loop and becomes unstable. This makes selecting such an op amp difficult as the circuit frequency increases. Current-to-frequency conversion circuits employing traditional integration networks typically have a linearity rating of 50 to 100 ppm. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides an integral unit structure and a current-frequency conversion circuit, which can be applied in the current-frequency conversion circuit to significantly improve the nonlinear index of this type of circuit. The linearity index of the current-frequency conversion circuit using the new integral structure can be improved by about 10 times.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An integration unit structure, including a first-stage operational amplifier U1, a second-stage operational amplifier U2, a resistor R1, a compensation resistor R2, a filter capacitor C1, an integration capacitor C2 and a compensation capacitor C3;

[0007] Input current I in Connect one end of the resistor R1 and the filter capacitor C1 respectively, and the other end of the resistor R1 is connected to the inverting input terminal of the first-stage operational amplifier U1, one end of the compensation capacitor C3 and one end of the integration capacitor C2 respectively;

[0008] The other end of the filter capacitor C1 is connected to the non-inverting input terminal of the first-stage operational amplifier U1 and the other end of the compensation capacitor C3 respectively; the output terminal of the first-stage operational amplifier U1 is connected to the non-inverting input terminal of the second-stage operational amplifier U2, and the output terminal of the second-stage operational amplifier U2 is connected to one end of the compensation resistor R2 and the inverting input terminal of the second-stage operational amplifier U2 respectively; the other end of the integrating capacitor C2 is connected to the other end of the compensation resistor R2;

[0009] The positive power supply terminals of the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are both connected to the voltage Vcc; the negative power supply terminals of the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are both grounded and connected to the other end of the filter capacitor C1.

[0010] Preferably, the first-stage operational amplifier U1 is an operational amplifier with high input impedance.

[0011] Preferably, the second-stage operational amplifier U2 is a high-speed operational amplifier.

[0012] Preferably, the value range of the filter capacitor C1 is 0.1uF to 0.47uF.

[0013] Preferably, the integral capacitor C2 is a polypropylene capacitor with a value ranging from 0.1uF to 0.33uF.

[0014] Preferably, the compensation capacitor C3 has a value ranging from 0.47uF to 1uF.

[0015] Preferably, the resistance of the resistor R1 ranges from 50 to 100 ohms.

[0016] Preferably, the resistance range of the compensation resistor R2 is 1 to 10 ohms.

[0017] A current-frequency conversion circuit comprises the integration unit structure as described in any one of the above.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects:

[0019] The present invention proposes an integration unit structure. Based on the principle of charge balance, the integration unit includes a critical input charge and a charge-balancing intersection. A cascaded integration network with compensation includes two operational amplifiers. The first-stage operational amplifier uses a high-input-impedance operational amplifier to ensure the zero-point specification requirement of the entire circuit. The second-stage operational amplifier uses a high-speed operational amplifier to ensure the circuit's response speed. To match the speed of the input feedback intersection, a compensation capacitor that can adjust the response speed is designed at the input of the first-stage operational amplifier. To improve the stability of the integration network, a compensation resistor is designed at the output of the second-stage operational amplifier. When the operating frequency of the current-to-frequency conversion circuit increases, the cascaded integration structure meets the higher operating frequency requirement of the loop. The compensation network effectively balances the instability of the loop caused by the increased operating frequency, thereby ensuring that the current-to-frequency conversion circuit has excellent nonlinearity. This design eliminates the specification limitations of individual devices, simplifies the circuit structure, and, through engineering practice, significantly reduces the nonlinearity of the current-to-frequency conversion circuit compared to existing integration networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the schematic diagram of the cascaded integrator network after compensation of the current-frequency conversion circuit. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0022] The integrator network unit is one of the core units of the current-to-frequency conversion circuit and is also one of the main sources of nonlinearity errors. The output of the integrator can be approximated as a triangle wave, which can be expanded according to the Fourier series when the full-scale output is:

[0023]

[0024] As can be seen from equation (1), a standard triangle wave is composed of an infinite number of sinusoidal functions. If the response speed of the integration network is limited, the high-frequency harmonic components will be attenuated, which will cause waveform distortion and thus deteriorate the nonlinearity index. Generally speaking, when the integration network can pass a signal with a frequency 300 times the fundamental frequency, the triangle wave signal will not produce nonlinear distortion and is considered to have sufficient accuracy, thereby ensuring the accuracy of the nonlinearity index of the current-to-frequency conversion circuit.

[0025] like Figure 1 As shown, a cascaded integrator network after compensation is added, an integration unit structure in the present invention includes a first-stage operational amplifier U1, a second-stage operational amplifier U2, a resistor R1, a compensation resistor R2, a filter capacitor C1, an integration capacitor C2 and a compensation capacitor C3.

[0026] Input current I in The resistor R1 and one end of the filter capacitor C1 are connected respectively, and the other end of the resistor R1 is connected respectively to the inverting input end of the first-stage operational amplifier U1, one end of the compensation capacitor C3 and one end of the integration capacitor C2.

[0027] The other end of the filter capacitor C1 is respectively connected to the non-inverting input terminal of the first-stage operational amplifier U1 and the other end of the compensation capacitor C3; the output end of the first-stage operational amplifier U1 is connected to the non-inverting input terminal of the second-stage operational amplifier U2, and the output end of the second-stage operational amplifier U2 is respectively connected to one end of the compensation resistor R2 and the inverting input terminal of the second-stage operational amplifier U2; the other end of the integrating capacitor C2 is connected to the other end of the compensation resistor R2.

[0028] The positive power supply terminals of both the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are connected to voltage Vcc; the negative power supply terminals of both the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are grounded and connected to the other end of filter capacitor C1. First-stage operational amplifier U1 uses a high-input impedance operational amplifier. Second-stage operational amplifier U2 uses a high-speed operational amplifier. Filter capacitor C1 has a value range of 0.1uF to 0.47uF. Integrating capacitor C2 is a polypropylene capacitor with a value range of 0.1uF to 0.33uF. Compensation capacitor C3 has a value range of 0.47uF to 1uF. Resistor R1 has a resistance range of 50 to 100 ohms. Compensation resistor R2 has a resistance range of 1 to 10 ohms.

[0029] The integrator of the present invention adopts a two-stage operational amplifier follower connection. The input end of the first-stage operational amplifier U1 adds a compensation capacitor C3 for adjusting the loop response speed, and the output end of the second-stage high-speed operational amplifier U2 adds a compensation resistor R2 for improving the loop stability. When the scale factor of the current-frequency conversion circuit increases, it not only ensures the response speed and stability of the integration network, but also effectively matches the response speed of the entire current-frequency conversion circuit through compensation, and ultimately effectively reduces the nonlinearity index of the entire current-frequency conversion circuit.

[0030] The current-frequency conversion circuit of the present invention includes an integration unit, a logic unit, a reference current unit, and a switch unit. According to the principle of charge balance, the integration unit includes a critical input charge and a point of intersection of balanced charges. The cascade integration network with compensation includes two stages of operational amplifiers. The first stage operational amplifier uses an operational amplifier with high input impedance to ensure the zero-point index requirement of the entire circuit. The second stage operational amplifier uses a high-speed operational amplifier to ensure the response speed requirement of the circuit. At the same time, in order to match the speed of the input feedback intersection, a compensation capacitor that can adjust the response speed is designed at the input end of the first stage operational amplifier. In order to improve the stability of the integration network, a compensation resistor is designed at the output end of the second stage operational amplifier. When the operating frequency of the current-frequency conversion circuit is increased, the higher operating frequency requirement of the loop is met through the cascade integration structure. The instability of the loop caused by the increase in the operating frequency is well balanced through the compensation network, thereby ensuring that the current-frequency conversion circuit has a good nonlinearity index.

Claims

1. An integration unit circuit, characterized in that: It includes a first-stage operational amplifier U1, a second-stage operational amplifier U2, a resistor R1, a compensation resistor R2, a filter capacitor C1, an integral capacitor C2 and a compensation capacitor C3; Input current I in Connect one end of the resistor R1 and the filter capacitor C1 respectively, and the other end of the resistor R1 is connected to the inverting input terminal of the first-stage operational amplifier U1, one end of the compensation capacitor C3 and one end of the integration capacitor C2 respectively; The other end of the filter capacitor C1 is connected to the non-inverting input terminal of the first-stage operational amplifier U1 and the other end of the compensation capacitor C3 respectively; the output terminal of the first-stage operational amplifier U1 is connected to the non-inverting input terminal of the second-stage operational amplifier U2, and the output terminal of the second-stage operational amplifier U2 is connected to one end of the compensation resistor R2 and the inverting input terminal of the second-stage operational amplifier U2 respectively; the other end of the integrating capacitor C2 is connected to the other end of the compensation resistor R2; The positive power supply terminals of the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are both connected to the voltage Vcc; the negative power supply terminals of the first-stage operational amplifier U1 and the second-stage operational amplifier U2 are both grounded and connected to the other end of the filter capacitor C1; the first-stage operational amplifier U1 uses an operational amplifier with high input impedance; the second-stage operational amplifier U2 uses a high-speed operational amplifier; the value range of the filter capacitor C1 is 0.1uF to 0.47uF; the integral capacitor C2 is a polypropylene capacitor with a value range of 0.1uF to 0.33uF; the value range of the compensation capacitor C3 is 0.47uF to 1uF; the resistance range of the resistor R1 is 50 to 100 ohms; the resistance range of the compensation resistor R2 is 1 to 10 ohms.

2. A current-frequency conversion circuit, characterized in that: The invention comprises the integration unit circuit as claimed in claim 1.

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