AD sampling signal processing method, circuit and device

Abstract

The invention relates to the technical field of circuit sampling, and discloses an AD sampling signal processing method, circuit and device. A group of sampling circuits with adjustable sampling value domains, namely two-stage series sampling circuits, are added on the aspect of a hardware circuit, and a value domain database is established in a software part; a large-range sampling domain is converted into a controllable small-range sampling domain, and the sampling precision of the system is related to the precision of an AD chip and the range of the small-range sampling domain, so that the sampling precision in a full-value domain range is improved. According to the mode, the AD acquisition precision is improved, the design cost is saved, and the method can be widely applied to occasions such as temperature measurement, IF measurement and the like which need high-precision AD sampling and have no continuous large-amplitude hopping of sampling signals, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit sampling, and in particular to a method, circuit and device for processing AD sampling signals. Background Art

[0002] AD sampling is a method of converting analog signals into digital signals. Its accuracy is mainly related to the target value range and the accuracy (number of bits) of the AD chip.

[0003] In practice, the AD sampling accuracy is inversely proportional to the target value range (i.e., the larger the target value range, the lower the accuracy), and is directly proportional to the accuracy of the AD chip (i.e., the higher the number of AD bits, the higher the accuracy). Taking the AD sampling of temperature signals as an example, without considering interference factors such as nonlinear distortion and white noise of the circuit, the theoretical AD sampling accuracy is the ratio of the full value range to the total AD value. If the measurement value range is -40°C to 100°C and a 12-bit AD chip is used, the theoretical AD sampling accuracy is 140 / 212=0.034°C. Improving the sampling accuracy can be achieved by reducing the sampling value range or improving the accuracy of the AD chip, but reducing the sampling value range may not meet the system requirements, and improving the accuracy of the AD chip will bring high costs, and even no finished products can meet the requirements.

[0004] In many cases, when the sampling accuracy does not meet the requirements (for example, the system requires temperature stability of ±0.1°C, and the temperature measurement accuracy under normal circumstances generally needs to be less than 0.01°C to be guaranteed), the common sampling and multiple-channel temperature measurement method is used to solve the problem, that is, in addition to full-range AD sampling, AD sampling is performed near the temperature control point in a small target range to improve the temperature accuracy in a small area. This method can effectively ensure the accuracy near the fixed temperature control point, but it cannot meet the requirements of high-precision temperature measurement in the full range (such as non-fixed temperature control point requirements, etc.). It is also possible to use a multi-channel temperature measurement method (that is, reducing the range of each AD sampling so that its accuracy meets the requirements, and combining multiple ADs to meet the range requirements) to ensure the accuracy index in the full range, but it requires multiple acquisition circuits, which takes up too many system resources and increases hardware costs. It can be seen that the accuracy of AD sampling in the prior art is low and the hardware cost is high. Summary of the invention

[0005] The present invention provides a method, circuit and device for processing an AD sampling signal, so as to solve the problems of low precision and high hardware cost in AD sampling in the prior art.

[0006] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0007] In a first aspect, the present invention provides a method for processing an AD sampling signal, which is applied to an AD sampling circuit, wherein the AD sampling circuit comprises a first-stage differential amplifier, a second-stage differential amplifier connected to the first-stage differential amplifier, and a CPU, wherein both the first-stage differential amplifier and the second-stage differential amplifier are connected to the CPU, and the processing method comprises:

[0008] Determine the value range database;

[0009] The first-stage differential amplifier is used to convert the full-range signal variation range of the previous-stage analog signal into the value range of the final-stage AD, and then the converted analog signal is transmitted to the AD1 channel of the subsequent-stage CPU;

[0010] The CPU retrieves the data of the corresponding value range from the value range database according to the sampling value of the AD1 channel, and outputs it to the second-stage differential amplifier;

[0011] The second-stage differential amplifier is used to amplify the corresponding segment voltage in the signal level again and transmit it to the AD2 channel of the subsequent CPU;

[0012] The CPU reads the sampling value of the AD2 channel, and determines the final sampling value based on the sampling value of the AD2 channel.

[0013] Optionally, the determining of the value range database includes:

[0014] During the debugging process, a resistance source is used to generate the resistance values ​​of the platinum resistors in the range of [-45°C, 125°C] with the value range of the second-stage differential amplifier as the interval;

[0015] The control value of the second-stage differential amplifier output at the set ratio during the current input is scanned out, and the control value is used as the corresponding value of the current input value and recorded in the value range database.

[0016] Optionally, the setting ratio is set to 1 / 2.

[0017] Optionally, the value range of the second-stage differential amplifier is controlled by a subsequent-stage CPU.

[0018] Optionally, determining the final sampling value based on the sampling value of the AD2 channel includes:

[0019] The sampling value of the AD2 channel is added to the corresponding baseline sampling value in the value domain database as the final sampling value of the current analog quantity.

[0020] In a second aspect, the present application provides an AD sampling circuit, comprising: a first-stage differential amplifier, a second-stage differential amplifier connected to the first-stage differential amplifier, and a CPU, wherein both the first-stage differential amplifier and the second-stage differential amplifier are connected to the CPU.

[0021] In a third aspect, the present application provides an AD sampling device, comprising the AD sampling circuit described in the second aspect.

[0022] Beneficial effects:

[0023] The present application provides a method for processing an AD sampling signal. In terms of the hardware circuit, a set of sampling circuits with adjustable sampling value ranges is added, namely, a two-stage series sampling circuit. The software part establishes a value range database; the large-range sampling domain is converted into a controllable small-range sampling domain. The sampling accuracy of the system is related to the accuracy of the AD chip and the range of the small-range sampling domain. Therefore, the sampling accuracy within the full value range is improved. This method improves the AD acquisition accuracy and saves design costs. It can be widely used in temperature measurement, IF measurement and other occasions that require high-precision AD sampling and the sampling signal does not have continuous large-amplitude jumps, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flowchart of a method for processing an AD sampling signal according to a preferred embodiment of the present invention;

[0025] Figure 2 A hardware block diagram of an AD sampling circuit according to a preferred embodiment of the present invention;

[0026] Figure 3 The hardware block diagram of the temperature sampling circuit of the preferred embodiment of the present invention;

[0027] Figure 4 4 is a temperature sampling circuit diagram of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the usual meanings understood by persons with ordinary skills in the field to which the present invention belongs. The "first level", "second level" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, similar words such as "one" or "one" do not indicate quantity restrictions, but indicate the existence of at least one. Similar words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0030] See also Figure 1 The present application provides a method for processing an AD sampling signal, which is applied to an AD sampling circuit. The AD sampling circuit includes a first-stage differential amplifier, a second-stage differential amplifier connected to the first-stage differential amplifier, and a CPU. The first-stage differential amplifier and the second-stage differential amplifier are both connected to the CPU. The processing method includes:

[0031] Determine the value range database;

[0032] The first-stage differential amplifier is used to convert the full-range signal variation range of the previous-stage analog signal into the value range of the final-stage AD, and then the converted analog signal is transmitted to the AD1 channel of the subsequent-stage CPU;

[0033] The CPU retrieves the data of the corresponding value range from the value range database based on the sampling value of the AD1 channel and outputs it to the second-stage differential amplifier.

[0034] In this step, it is worth noting that the range database is based on the sampled value. For example, the range [-40, 120] is segmented. For a 12-bit AD, the resolution is 4096 / 160. A corresponding value is established for each step of 5, that is, the range 4096 is divided into 320 parts, each corresponding to a coefficient. After reading the value of AD1, the corresponding coefficient is called to control the sampled range of the second-stage amplifier.

[0035] The second-stage differential amplifier is used to amplify the corresponding segment voltage in the signal level again and transmit it to the AD2 channel of the subsequent CPU.

[0036] The CPU reads the sampling value of the AD2 channel, and determines the final sampling value based on the sampling value of the AD2 channel.

[0037] In this embodiment, the gain factors of the differential amplifier I and the differential amplifier II are fixed values, wherein the value range (sampling range) of the differential amplifier I is a fixed value (the full value range of the input analog signal).

[0038] The above-mentioned AD sampling signal processing method adds a set of sampling circuits with adjustable sampling value range in the hardware circuit, that is, a two-stage series sampling circuit, and the software part establishes a value range database; the large-range sampling domain is converted into a controllable small-range sampling domain. The sampling accuracy of the system is related to the accuracy of the AD chip and the range of the small-range sampling domain. Therefore, the sampling accuracy within the full value range is improved. This method improves the AD acquisition accuracy and saves design costs. It can be widely used in temperature measurement, IF measurement and other occasions that require high-precision AD sampling and the sampling signal does not have continuous large jumps, and has broad application prospects.

[0039] Below, through a complete example, the steps of the above-mentioned AD sampling signal processing method are described as follows:

[0040] like Figure 2 As shown, first, the first-stage differential amplifier (differential amplifier I) converts the full-range signal change range in the previous-stage analog signal into the value range of the final-stage AD. For example, if the full-range signal change in the previous-stage analog signal is [0.98V, 0.99V] and the sampling range of the final-stage AD is [0V, 5V], then the first-stage differential amplifier amplifies the value change [0.98V, 0.99V] to [0V, 5V].

[0041] Then, it is sent to the AD1 channel of the subsequent CPU. The CPU retrieves the data of the corresponding value range from the value range database based on the sampling value of AD1, and outputs it to the second-stage differential amplifier (differential amplifier II). The differential amplifier II is controlled to amplify the small value range voltage near the signal level again and send it to the subsequent AD2 to obtain higher sampling accuracy. The value range of the differential amplifier II is controlled by the subsequent CPU.

[0042] Specifically, in an example of CPU control, taking the AD sampling range [0V, 5V], the differential amplifier II magnification of 100, and the analog signal level of about 1V after passing through the differential amplifier I as an example, the CPU reads the AD1 sampling value (1V), reads the corresponding data from the value range database (established by calibration during debugging), controls the differential amplifier II value range to [0.975V, 1.025V], reads the AD2 data, and obtains the corresponding sampling value of the current analog quantity through calculation. Since the differential amplifier magnification is 100, its sampling accuracy is 100 times that of the AD1 sampling accuracy (full value range sampling accuracy). Among them, the specific calculation method is to add the AD2 sampling value to the corresponding baseline sampling value in the value range database to obtain the corresponding sampling value of the current analog quantity.

[0043] In one example, the value range of the differential amplifier II is controlled by the post-stage CPU, including: assuming that the AD1 sampling value is 3001, the data segment length of the value range database is 15, and the step length is 5, that is, in the database, the three data segments 2990, 2995, and 3000 all cover 3001, and the ranges of these three data segments are [2990, 3005], [2995, 3010], and [3000, 3015] respectively. However, due to the nonlinearity of the operational amplifier, only the 1 / 3-2 / 3 segment of the value range is taken, among which the position of 3001 in the 2990 data segment is greater than 2 / 3, so it is discarded; in the 3000 data segment, the position of 3001 is less than 1 / 3, so it is discarded, so the data value corresponding to 2995 is selected to control the value range of the second-stage differential amplifier.

[0044] In addition, for understanding the corresponding baseline sampling values ​​in the range database, it should be pointed out that, if the AD1 sampling value is 3001, the corresponding temperature value when calibrating data segment 2995 in the range database is 76°, and the AD2 sampling value is 1640, then the final value is 76+1640*15 / 4096=82.0058°.

[0045] It is worth mentioning that factors such as the nonlinear distortion zone of the op amp (or the use of rail-to-rail op amps, and protection circuits when the op amp output exceeds the AD input) need to be considered when designing the circuit.

[0046] In one example, if Figure 3 As shown, take the temperature measurement AD acquisition circuit as an example. The target requires a temperature measurement range of -40℃~120℃, a temperature control accuracy of 0.1℃, and a temperature measurement accuracy of 0.01℃. Temperature control and temperature measurement share the same CPU, and it is planned to use ADμC841. The chip has 8 12-bit AD inputs, 2 12-bit DA outputs, and 2 16-bit PWM outputs. In order to reduce costs, it is planned to use the CPU's own AD, and the sampling period is 0.1s. If the conventional method is used directly for AD acquisition, considering the nonlinear distortion of the op amp, the design sampling range is -45℃~125℃, and the theoretical temperature measurement accuracy is about 0.042℃, which does not meet the requirements. The temperature sampling target is the heating of the temperature control system. Its temperature signal is a slow-changing signal, and there will be no jump greater than 1℃ in adjacent sampling cycles. Therefore, the full-range AD accuracy improvement technology can be used. When sampling, the local signal is re-amplified. If the re-amplified sampling range is 10℃, the theoretical temperature measurement accuracy can reach 0.0025℃. Meet the design requirements.

[0047] In one example, if Figure 4As shown in the figure, when the temperature measurement range is required to be -40℃~120℃, the sampling range is designed to be -45℃~125℃ in consideration of factors such as the nonlinear distortion of the operational amplifier. The resistance change of the temperature sensor (platinum resistor) within the designed temperature range is converted into a voltage change of 0V~2.5V (AD sampling range of ADμC841) by the sampling circuit I composed of the bridge, voltage follower, differential amplifier and other circuits, and transmitted to one AD input (AD1) of the CPU. At the same time, the voltage change is transmitted to another AD input (AD2) of the CPU through the sampling circuit II composed of the voltage follower, differential amplifier and other circuits (taking the sampling interval of 5℃ as an example, the amplification factor of the differential amplifier II is 34 at this time); after the CPU reads the AD1 value, it selects the corresponding data in the value range database to control the value range of the sampling circuit II; the CPU reads the AD2 value, combines the value range of the sampling circuit II, and calculates the current temperature through the formula. Taking the AD accuracy of 12 bits as an example, the theoretical temperature measurement accuracy after sampling by AD1 is 170 / 212=0.042°C, and the theoretical temperature measurement accuracy after sampling by AD2 is 10 / 212=0.0024°C.

[0048] Due to the discreteness of the device, when debugging the circuit, calibration is first required, that is, determining the range database. Use a multi-function tester (or other precision resistance source) to generate platinum resistance values ​​in the range of [-45℃, 125℃] with an interval of 1℃ (the range of differential amplifier II) (taking a 1k platinum resistor with a temperature coefficient of 3850ppm as an example, its resistance is 1000Ω at 0℃, and its resistance is 1000+t×3.85(Ω) at t℃). Use the auxiliary scanning program to scan out the control value when the output of differential amplifier II is at 1 / 2 during the current input, as the corresponding value of the current input value, and record it in the range database. When sampling, select the appropriate control value (reference value) from the range database based on the AD1 sampling value, so that the AD2 sampling value is preferably in the range of [1 / 2, 2 / 3] of the output of differential amplifier II (this range has the best linearity). When calculating the temperature, AD2 = current reference temperature value + 5×(AD2 sampling value-2048) / 4096. Wherein, the current reference temperature value is the temperature value corresponding to the selected reference value, 5 is the value range of the differential amplifier II, and since the reference value corresponding to the temperature during calibration is 1 / 2 of the value range, the sample value needs to be subtracted by 1 / 2 of the resolution 212, and 4096 is the resolution 212.

[0049] The present application also provides an AD sampling circuit, comprising: a first-stage differential amplifier, a second-stage differential amplifier connected to the first-stage differential amplifier, and a CPU, wherein both the first-stage differential amplifier and the second-stage differential amplifier are connected to the CPU.

[0050] The AD sampling circuit can implement various embodiments of the above-mentioned AD sampling signal processing method and achieve the same beneficial effects, which will not be described in detail here.

[0051] The present application also provides an AD sampling device, including the above-mentioned AD sampling circuit. The AD sampling device can implement various embodiments of the above-mentioned AD sampling circuit and achieve the same beneficial effects, which will not be described in detail here.

[0052] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for processing an AD sampling signal, applied to an AD sampling circuit, wherein the AD sampling circuit comprises a first-stage differential amplifier, a second-stage differential amplifier connected to the first-stage differential amplifier, and a CPU, wherein both the first-stage differential amplifier and the second-stage differential amplifier are connected to the CPU, characterized in that: The processing method comprises: Determine the value range database; The first-stage differential amplifier is used to convert the full-range signal variation range of the previous-stage analog signal into the value range of the final-stage AD, and then the converted analog signal is transmitted to the AD1 channel of the subsequent-stage CPU; The CPU retrieves the data of the corresponding value range from the value range database according to the sampling value of the AD1 channel, and outputs it to the second-stage differential amplifier; The second-stage differential amplifier is used to amplify the corresponding segment voltage in the signal level again and transmit it to the AD2 channel of the subsequent CPU; The CPU reads the sampling value of the AD2 channel, and determines the final sampling value based on the sampling value of the AD2 channel.

2. The method for processing an AD sampling signal according to claim 1, characterized in that: The determined value range database includes: During the debugging process, a resistance source is used to generate the resistance values ​​of the platinum resistors in the range of [-45°C, 125°C] with the value range of the second-stage differential amplifier as the interval; The control value of the second-stage differential amplifier output at the set ratio during the current input is scanned out, and the control value is used as the corresponding value of the current input value and recorded in the value range database.

3. The method for processing an AD sampling signal according to claim 2, characterized in that: The setting ratio is 1 / 2.

4. The method for processing an AD sampling signal according to claim 1, characterized in that: The value range of the second-stage differential amplifier is controlled by the subsequent CPU.

5. The method for processing AD sampling signals according to claim 1, characterized in that: The determining of the final sampling value based on the sampling value of the AD2 channel includes: The sampling value of the AD2 channel is added to the corresponding baseline sampling value in the value domain database as the final sampling value of the current analog quantity.

6. An AD sampling circuit, characterized in that: include: A first-stage differential amplifier, a second-stage differential amplifier connected to the first-stage differential amplifier, and a CPU. Both the first-stage differential amplifier and the second-stage differential amplifier are connected to the CPU.

7. An AD sampling device, characterized in that: Includes the AD sampling circuit as claimed in claim 5.

Images