An impedance measurement system based on noise orthogonal technology

Abstract

The present invention belongs to the technical field of impedance measurement, and particularly relates to an impedance measurement system based on noise orthogonal technology, comprising: a current source, a noise orthogonal pulse modulator, a chopper switch, an impedance to be measured, a synchronous clock unit, and a noise orthogonal analog-to-digital converter; the noise orthogonal pulse modulator outputs a signal to the chopper switch to modulate the chopper switch; the input of the chopper switch is connected to a pair of current sources, and the output is connected to the impedance to be measured; the impedance to be measured is connected to the input of the noise orthogonal analog-to-digital converter; the synchronous clock unit outputs a synchronous sampling clock signal, which is respectively connected to the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter. The impedance measurement system based on noise orthogonal technology of the present invention does not require a sine wave generator, has the advantages of low power consumption, small area, and low cost. At the same time, the signal is completely decoupled from the quantization noise, and the resolution is higher.

Description

Technical Field

[0001] The present invention belongs to the technical field of impedance measurement, and particularly relates to an impedance measurement system based on noise orthogonal technology. Background Art

[0002] Impedance measurement systems have a wide range of applications. An impedance measurement system can obtain environmental information by measuring an impedance-type sensor; it can also obtain physiological information by measuring bio-impedance; and it can also measure the chemical reaction state by measuring the impedance of electrochemical products.

[0003] In a traditional impedance measurement system, a sinusoidal current excitation with a specific measurement frequency is generally applied to the impedance to be measured. After the current is multiplied by the impedance to obtain a voltage, the voltage is processed such as signal amplification and filtering by an analog front end and then input into an analog-to-digital converter. As Figure 1 shown. Generally speaking, in order to ensure the impedance measurement accuracy, a sine wave generator is required, and the sine wave generator has high power consumption, large area, and high cost. Therefore, the traditional impedance test system has problems of high power consumption, large area, and high cost.

[0004] At the same time, in order to improve the resolution, in a traditional impedance measurement system, the analog-to-digital converter will adopt a noise shaping technology, as Figure 1 shown. In a traditional noise shaping method, its noise transfer function is often based on (1 - Z -1 ) L , where L is a positive integer representing the order of noise shaping. In its frequency spectrum, according to the order of noise shaping, a noise shaping effect of L * 20 dB / dec is presented, where dB represents decibel and dec represents decade, as Figure 2 shown. The problem with this kind of noise shaping is that the signal and the noise transfer function and quantization noise are not completely decoupled, and there is still a quantization noise component at the signal frequency, as Figure 3 shown. Therefore, in an impedance test system adopting the traditional noise shaping technology, there is still coupling between the signal and the quantization noise.

[0005] The traditional impedance test system adopting sine excitation and noise shaping technology has problems of high power consumption, large area, high cost, and still coupling between the signal and the quantization noise. Summary of the Invention

[0006] In order to solve the above technical problems existing in the prior art, the present invention proposes an impedance measurement system based on noise orthogonal technology, and its specific technical solution is as follows:

[0007] An impedance measurement system based on noise orthogonal technology, comprising: a current source, a noise orthogonal pulse modulator, a chopper switch, an impedance to be measured, a synchronous clock unit, and a noise orthogonal analog-to-digital converter; the noise orthogonal pulse modulator outputs a signal to the chopper switch to modulate the chopper switch; the input of the chopper switch is connected to a pair of current sources, and the output is connected to the impedance to be measured; the impedance to be measured is connected to the input of the noise orthogonal analog-to-digital converter; both ends of the synchronous clock unit are respectively connected to the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter.

[0008] Further, the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter adopt the same noise transfer function structure.

[0009] Further, the synchronous clock unit outputs synchronous sampling clock signals with signal frequencies of f S1 and f S2 , which are respectively connected to the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter.

[0010] Further, the noise transfer function of the noise orthogonal pulse modulator is (1 - Z -N1 ) L1 , where L1 is a positive integer and N1 is a positive integer greater than 1; the sampling frequency of the noise orthogonal pulse modulator is f S1 , which is the frequency of the synchronous sampling clock signal output by the synchronous clock unit to the noise orthogonal pulse modulator, and the measurement frequency of the impedance to be measured is f 0 , satisfying the relationship f S1 = N1 * f 0 .

[0011] Further, the noise transfer function of the noise orthogonal analog-to-digital converter is (1 - Z -N2 ) L2 , where L2 is a positive integer and N2 is a positive integer greater than 1 and N2 = m * N1, m is a positive integer; the sampling frequency of the noise orthogonal analog-to-digital converter is f S2 , which is the frequency of the synchronous sampling clock signal output by the synchronous clock unit to the noise orthogonal analog-to-digital converter, and the measurement frequency of the impedance to be measured is f 0 , satisfying the relationship f S2 = N2 * f 0 .

[0012] Further, the impedance to be measured includes: an impedance-type sensor, a bio-impedance, and an electrochemical reactant impedance.

[0013] Beneficial effects:

[0014] The impedance measurement system based on noise orthogonal technology of the present invention does not require a sine wave generator, has the advantages of low power consumption, small area, and low cost. At the same time, the signal and quantization noise are completely decoupled, and the resolution is higher. Brief Description of the Drawings

[0015] Figure 1 is a schematic structural diagram of a traditional impedance test system;

[0016] Figure 2 is a schematic diagram of coordinate parameters of traditional noise shaping technology;

[0017] Figure 3 is a schematic diagram of the mutual coupling between the signal and quantization noise in traditional noise shaping technology;

[0018] Figure 4 is a schematic diagram of an impedance measurement system based on noise orthogonal technology of the present invention;

[0019] Figure 5 is a schematic diagram of the complete decoupling between the signal and quantization noise in the noise orthogonal technology of the present invention;

[0020] Figure 6 is a spectrogram of the noise orthogonal pulse modulator of the impedance measurement system based on noise orthogonal technology according to an embodiment of the present invention;

[0021] Figure 7 is a spectrogram of the noise orthogonal analog-to-digital converter of the impedance measurement system based on noise orthogonal technology according to an embodiment of the present invention. Detailed Description of the Invention

[0022] In order to make the objectives, technical solutions and technical effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings of the specification and embodiments.

[0023] As shown in Figure 4 and Figure 5 , an impedance measurement system based on noise orthogonal technology includes: a current source, a noise orthogonal pulse modulator, a chopper switch, an impedance to be measured, a synchronous clock unit, and a noise orthogonal analog-to-digital converter. The specific technical solution for impedance measurement is as follows:

[0024] The output signal of the noise orthogonal pulse modulator is used to modulate the chopper switch. The input of the chopper switch is connected to a pair of current sources, and the output is connected to the impedance to be measured. The impedance to be measured is connected to the input of the noise orthogonal analog-to-digital converter. At the same time, a synchronous clock unit outputs a synchronous sampling clock signal, which is respectively connected to the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter. The noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter adopt the same noise transfer function.

[0025] The noise orthogonal pulse modulator has a noise transfer function of (1 - Z -N1 ) L1 , where L1 is a positive integer and N1 is a positive integer greater than 1; the sampling frequency of the noise orthogonal pulse modulator is f S1, the measurement frequency of the impedance to be measured is f 0 , and they satisfy f S1 = N1 * f 0 .

[0026] For the noise orthogonal analog-to-digital converter, its noise transfer function is (1 - Z -N2 ) L2 , where L2 is a positive integer, N2 is a positive integer greater than 1 and N2 = m * N1, m is a positive integer; the sampling frequency of the noise orthogonal analog-to-digital converter is f S2 , the measurement frequency of the impedance to be measured is f 0 , and they satisfy f S2 = N2 * f 0 .

[0027] The impedance to be measured can be an impedance-type sensor, a bio-impedance, or a reactant impedance of a chemical reaction.

[0028] The principle that the impedance measurement system of the present invention has low power consumption, small area, low cost, and higher resolution can be explained from two aspects.

[0029] First, a noise orthogonal pulse modulator is used instead of the sine wave generator in the traditional method. Since the noise transfer function of the noise orthogonal pulse modulator is (1 - Z -N1 ) L1 , the sampling frequency is f S1 , and the measurement frequency is f 0 , and they satisfy f S1 = N1 * f 0 , so the measurement frequency f 0 is at the zero point of the noise transfer function of the noise orthogonal pulse modulator. At the measurement frequency f 0 , the noise orthogonal pulse modulator has no quantization noise, and the signal-to-noise ratio is the same as that of the sine wave generator. Moreover, the noise orthogonal pulse modulator is implemented in a fully digital manner with single-bit output, so it has low power consumption, small area, and low cost.

[0030] In addition, since the noise transfer function of the noise orthogonal analog-to-digital converter is (1 - Z -N2 ) L2 , the sampling frequency is f S2 , and the measurement frequency is f 0 , and they satisfy f S2 = N2 * f 0 , so the measurement frequency f 0 is at the zero point of the noise transfer function of the noise orthogonal analog-to-digital converter. At the measurement frequency f 0 , the noise orthogonal analog-to-digital converter also has no quantization noise. Therefore, the signal and the quantization noise are completely decoupled, and the resolution is higher.

[0031] Measurement is performed using the impedance measurement system based on the noise orthogonal technology proposed by the present invention. Specific examples are as Figure 6 and Figure 7 shown. In this embodiment, N1 = N2 = 8, L1 = L2 = 2, f S1 = f S2 = 8f 0 .

[0032] In this embodiment, the output signal of the noise orthogonal pulse modulator is used to modulate the chopper switch. The input of the chopper switch is connected to a pair of current sources, and the output is connected to the impedance to be measured. The impedance to be measured is connected to the input of the noise orthogonal analog-to-digital converter. At the same time, a synchronous clock unit outputs a synchronous sampling clock signal, which is respectively connected to the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter. The noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter adopt the same noise transfer function, which are (1 - Z -8 ) 2 and (1 - Z -8 ) 2 , respectively. The measurement frequency of the impedance to be measured is f 0 , which satisfies f S1 = f S2 = 8f 0 with the sampling frequencies f 0 S1 and f S2 .

[0033] In this embodiment, the measurement frequency f 0 is simultaneously at the zeros of the noise transfer functions of the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter. Therefore, at the measurement frequency f 0 , the noise orthogonal pulse modulator has no quantization noise, and the signal-to-noise ratio is the same as that of the sine wave generator. The noise orthogonal pulse modulator is implemented in a fully digital manner with a single-bit output, so it has low power consumption, small area, and low cost. At the same time, at the measurement frequency f 0 , the noise orthogonal analog-to-digital converter also has no quantization noise, and the signal is completely decoupled from the quantization noise, resulting in higher resolution.

[0034] It can be seen from the above embodiments that the impedance measurement system based on the noise orthogonal technology proposed by the present invention has the advantages of low power consumption, small area, low cost, and higher resolution. In the embodiments shown in Figure 6 and Figure 7 , there is no need for a sine wave generator, and only a single-bit noise orthogonal pulse modulator is required, so the power consumption is low, the area is small, and the cost is low. At the same time, due to the adoption of the noise orthogonal technology, the entire measurement system is completely unaffected by quantization noise, so the resolution is higher.

[0035] The above are only the preferred embodiments of the present invention and do not impose any formal restrictions on the present invention. Although the implementation process of the present invention has been described in detail above, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent replacements for some of the technical features. Any modifications, equivalent replacements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An impedance measurement system based on noise orthogonal technology, characterized in that, comprising: a current source, a noise orthogonal pulse modulator, a chopper switch, an impedance to be measured, a synchronous clock unit, and a noise orthogonal analog-to-digital converter; the noise orthogonal pulse modulator outputs a signal to the chopper switch to modulate the chopper switch; the input of the chopper switch is connected to a pair of current sources, and the output is connected to the impedance to be measured; the impedance to be measured is connected to the input of the noise orthogonal analog-to-digital converter; both ends of the synchronous clock unit are respectively connected to the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter; the noise orthogonal pulse modulator and the noise orthogonal analog-to-digital converter adopt the same noise transfer function structure; The synchronous clock unit outputs a synchronous sampling clock signal, and the signal frequencies are f S1 and f S2 , respectively connected to a noise quadrature pulse modulator and a noise quadrature analog-to-digital converter; The noise transfer function of the noise orthogonal pulse modulator is (1 - Z -N1 ) L1 , where L1 is a positive integer and N1 is a positive integer greater than 1; the sampling frequency of the noise orthogonal pulse modulator is f S1 , which is the frequency of the synchronous sampling clock signal output from the synchronous clock unit to the noise orthogonal pulse modulator, and the measurement frequency of the impedance to be measured is f 0 , satisfying the relationship f S1 = N1 * f 0 ; The noise transfer function of the noise orthogonal analog-to-digital converter is (1 - Z -N2 ) L2 , where L2 is a positive integer, N2 is a positive integer greater than 1 and N2 = m * N1, and m is a positive integer; the sampling frequency of the noise orthogonal analog-to-digital converter is f S2 , which is the frequency of the synchronous sampling clock signal output from the synchronous clock unit to the noise orthogonal analog-to-digital converter, and the measurement frequency of the impedance to be measured is f 0 , satisfying the relationship f S2 = N2 * f 0 .

2. The impedance measurement system based on noise orthogonal technology according to claim 1, characterized in that, the impedance to be measured includes: an impedance-type sensor, a bio-impedance, and an electrochemical reactant impedance.

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